nix/
unistd.rs

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068
3069
3070
3071
3072
3073
3074
3075
3076
3077
3078
3079
3080
3081
3082
3083
3084
3085
3086
3087
3088
3089
3090
3091
3092
3093
3094
3095
3096
3097
3098
3099
3100
3101
3102
3103
3104
3105
3106
3107
3108
3109
3110
3111
3112
3113
3114
3115
3116
3117
3118
3119
3120
3121
3122
3123
3124
3125
3126
3127
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138
3139
3140
3141
3142
3143
3144
3145
3146
3147
3148
3149
3150
3151
3152
3153
3154
3155
3156
3157
3158
3159
3160
3161
3162
3163
3164
3165
3166
3167
3168
3169
3170
3171
3172
3173
3174
3175
3176
3177
3178
3179
3180
3181
3182
3183
3184
3185
3186
3187
3188
3189
3190
3191
3192
3193
3194
3195
3196
3197
3198
3199
3200
3201
3202
3203
3204
3205
3206
3207
3208
3209
3210
3211
3212
3213
3214
3215
3216
3217
3218
3219
3220
3221
3222
3223
3224
3225
3226
3227
3228
3229
3230
3231
3232
3233
3234
3235
3236
3237
3238
3239
3240
3241
3242
3243
3244
3245
3246
3247
3248
3249
3250
3251
3252
3253
3254
3255
3256
3257
3258
3259
3260
3261
3262
3263
3264
3265
3266
3267
3268
3269
3270
3271
3272
3273
3274
3275
3276
3277
3278
3279
3280
3281
3282
3283
3284
3285
3286
3287
3288
3289
3290
3291
3292
3293
3294
3295
3296
3297
3298
3299
3300
3301
3302
3303
3304
3305
3306
3307
3308
3309
3310
3311
3312
3313
3314
3315
3316
3317
3318
3319
3320
3321
3322
3323
3324
3325
3326
3327
3328
3329
3330
3331
3332
3333
3334
3335
3336
3337
3338
3339
3340
3341
3342
3343
3344
3345
3346
3347
3348
3349
3350
3351
3352
3353
3354
3355
3356
3357
3358
3359
3360
3361
3362
3363
3364
3365
3366
3367
3368
3369
3370
3371
3372
3373
3374
3375
3376
3377
3378
3379
3380
3381
3382
3383
3384
3385
3386
3387
3388
3389
3390
3391
3392
3393
3394
3395
3396
3397
3398
3399
3400
3401
3402
3403
3404
3405
3406
3407
3408
3409
3410
3411
3412
3413
3414
3415
3416
3417
3418
3419
3420
3421
3422
3423
3424
3425
3426
3427
3428
3429
3430
3431
3432
3433
3434
3435
3436
3437
3438
3439
3440
3441
3442
3443
3444
3445
3446
3447
3448
3449
3450
3451
3452
3453
3454
3455
3456
3457
3458
3459
3460
3461
3462
3463
3464
3465
3466
3467
3468
3469
3470
3471
3472
3473
3474
3475
3476
3477
3478
3479
3480
3481
3482
3483
3484
3485
3486
3487
3488
3489
3490
3491
3492
3493
3494
3495
3496
3497
3498
3499
3500
3501
3502
3503
3504
3505
3506
3507
3508
3509
3510
3511
3512
3513
3514
3515
3516
3517
3518
3519
3520
3521
3522
3523
3524
3525
3526
3527
3528
3529
3530
3531
3532
3533
3534
3535
3536
3537
3538
3539
3540
3541
3542
3543
3544
3545
3546
3547
3548
3549
3550
3551
3552
3553
3554
3555
3556
3557
3558
3559
3560
3561
3562
3563
3564
3565
3566
3567
3568
3569
3570
3571
3572
3573
3574
3575
3576
3577
3578
3579
3580
3581
3582
3583
3584
3585
3586
3587
3588
3589
3590
3591
3592
3593
3594
3595
3596
3597
3598
3599
3600
3601
3602
3603
3604
3605
3606
3607
3608
3609
3610
3611
3612
3613
3614
3615
3616
3617
3618
3619
3620
3621
3622
3623
3624
3625
3626
3627
3628
3629
3630
3631
3632
3633
3634
3635
3636
3637
3638
3639
3640
3641
3642
3643
3644
3645
3646
3647
3648
3649
3650
3651
3652
3653
3654
3655
3656
3657
3658
3659
3660
3661
3662
3663
3664
3665
3666
3667
3668
3669
3670
3671
3672
3673
3674
3675
3676
3677
//! Safe wrappers around functions found in libc "unistd.h" header

use crate::errno::Errno;

#[cfg(any(
    all(feature = "fs", not(target_os = "redox")),
    all(feature = "process", linux_android)
))]
use crate::fcntl::at_rawfd;
#[cfg(not(target_os = "redox"))]
#[cfg(feature = "fs")]
use crate::fcntl::AtFlags;

#[cfg(feature = "fs")]
#[cfg(any(
    linux_android,
    freebsdlike,
    solarish,
    netbsdlike,
    target_os = "emscripten",
    target_os = "fuchsia",
    target_os = "hurd",
    target_os = "redox",
))]
use crate::fcntl::OFlag;
#[cfg(all(feature = "fs", bsd))]
use crate::sys::stat::FileFlag;
#[cfg(feature = "fs")]
use crate::sys::stat::Mode;
use crate::{Error, NixPath, Result};
#[cfg(not(target_os = "redox"))]
use cfg_if::cfg_if;
use libc::{
    c_char, c_int, c_long, c_uint, gid_t, mode_t, off_t, pid_t, size_t, uid_t,
};
use std::convert::Infallible;
#[cfg(not(target_os = "redox"))]
use std::ffi::CString;
use std::ffi::{CStr, OsStr, OsString};
use std::os::unix::ffi::{OsStrExt, OsStringExt};
use std::os::unix::io::{AsFd, AsRawFd, OwnedFd, RawFd};
use std::path::PathBuf;
use std::{fmt, mem, ptr};

feature! {
    #![feature = "fs"]
    #[cfg(linux_android)]
    pub use self::pivot_root::*;
}

#[cfg(any(freebsdlike, linux_android, target_os = "openbsd"))]
pub use self::setres::*;

#[cfg(any(freebsdlike, linux_android, target_os = "openbsd"))]
pub use self::getres::*;

feature! {
#![feature = "user"]

/// User identifier
///
/// Newtype pattern around `uid_t` (which is just alias). It prevents bugs caused by accidentally
/// passing wrong value.
#[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
pub struct Uid(uid_t);

impl Uid {
    /// Creates `Uid` from raw `uid_t`.
    pub const fn from_raw(uid: uid_t) -> Self {
        Uid(uid)
    }

    /// Returns Uid of calling process. This is practically a more Rusty alias for `getuid`.
    #[doc(alias("getuid"))]
    pub fn current() -> Self {
        getuid()
    }

    /// Returns effective Uid of calling process. This is practically a more Rusty alias for `geteuid`.
    #[doc(alias("geteuid"))]
    pub fn effective() -> Self {
        geteuid()
    }

    /// Returns true if the `Uid` represents privileged user - root. (If it equals zero.)
    pub const fn is_root(self) -> bool {
        self.0 == ROOT.0
    }

    /// Get the raw `uid_t` wrapped by `self`.
    pub const fn as_raw(self) -> uid_t {
        self.0
    }
}

impl From<Uid> for uid_t {
    fn from(uid: Uid) -> Self {
        uid.0
    }
}

impl From<uid_t> for Uid {
    fn from(uid: uid_t) -> Self {
        Uid(uid)
    }
}

impl fmt::Display for Uid {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        fmt::Display::fmt(&self.0, f)
    }
}

/// Constant for UID = 0
pub const ROOT: Uid = Uid(0);

/// Group identifier
///
/// Newtype pattern around `gid_t` (which is just alias). It prevents bugs caused by accidentally
/// passing wrong value.
#[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
pub struct Gid(gid_t);

impl Gid {
    /// Creates `Gid` from raw `gid_t`.
    pub const fn from_raw(gid: gid_t) -> Self {
        Gid(gid)
    }

    /// Returns Gid of calling process. This is practically a more Rusty alias for `getgid`.
    #[doc(alias("getgid"))]
    pub fn current() -> Self {
        getgid()
    }

    /// Returns effective Gid of calling process. This is practically a more Rusty alias for `getegid`.
    #[doc(alias("getegid"))]
    pub fn effective() -> Self {
        getegid()
    }

    /// Get the raw `gid_t` wrapped by `self`.
    pub const fn as_raw(self) -> gid_t {
        self.0
    }
}

impl From<Gid> for gid_t {
    fn from(gid: Gid) -> Self {
        gid.0
    }
}

impl From<gid_t> for Gid {
    fn from(gid: gid_t) -> Self {
        Gid(gid)
    }
}

impl fmt::Display for Gid {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        fmt::Display::fmt(&self.0, f)
    }
}
}

feature! {
#![feature = "process"]
/// Process identifier
///
/// Newtype pattern around `pid_t` (which is just alias). It prevents bugs caused by accidentally
/// passing wrong value.
#[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
pub struct Pid(pid_t);

impl Pid {
    /// Creates `Pid` from raw `pid_t`.
    pub const fn from_raw(pid: pid_t) -> Self {
        Pid(pid)
    }

    /// Returns PID of calling process
    #[doc(alias("getpid"))]
    pub fn this() -> Self {
        getpid()
    }

    /// Returns PID of parent of calling process
    #[doc(alias("getppid"))]
    pub fn parent() -> Self {
        getppid()
    }

    /// Get the raw `pid_t` wrapped by `self`.
    pub const fn as_raw(self) -> pid_t {
        self.0
    }
}

impl From<Pid> for pid_t {
    fn from(pid: Pid) -> Self {
        pid.0
    }
}

impl fmt::Display for Pid {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        fmt::Display::fmt(&self.0, f)
    }
}

/// Represents the successful result of calling `fork`
///
/// When `fork` is called, the process continues execution in the parent process
/// and in the new child.  This return type can be examined to determine whether
/// you are now executing in the parent process or in the child.
#[derive(Clone, Copy, Debug)]
pub enum ForkResult {
    /// This is the parent process of the fork.
    Parent {
        /// The PID of the fork's child process
        child: Pid
    },
    /// This is the child process of the fork.
    Child,
}

impl ForkResult {
    /// Return `true` if this is the child process of the `fork()`
    #[inline]
    pub fn is_child(self) -> bool {
        matches!(self, ForkResult::Child)
    }

    /// Returns `true` if this is the parent process of the `fork()`
    #[inline]
    pub fn is_parent(self) -> bool {
        !self.is_child()
    }
}

/// Create a new child process duplicating the parent process ([see
/// fork(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/fork.html)).
///
/// After successfully calling the fork system call, a second process will
/// be created which is identical to the original except for the pid and the
/// return value of this function.  As an example:
///
/// ```
/// use nix::{sys::wait::waitpid,unistd::{fork, ForkResult, write}};
///
/// match unsafe{fork()} {
///    Ok(ForkResult::Parent { child, .. }) => {
///        println!("Continuing execution in parent process, new child has pid: {}", child);
///        waitpid(child, None).unwrap();
///    }
///    Ok(ForkResult::Child) => {
///        // Unsafe to use `println!` (or `unwrap`) here. See Safety.
///        write(std::io::stdout(), "I'm a new child process\n".as_bytes()).ok();
///        unsafe { libc::_exit(0) };
///    }
///    Err(_) => println!("Fork failed"),
/// }
/// ```
///
/// This will print something like the following (order nondeterministic).  The
/// thing to note is that you end up with two processes continuing execution
/// immediately after the fork call but with different match arms.
///
/// ```text
/// Continuing execution in parent process, new child has pid: 1234
/// I'm a new child process
/// ```
///
/// # Safety
///
/// In a multithreaded program, only [async-signal-safe] functions like `pause`
/// and `_exit` may be called by the child (the parent isn't restricted). Note
/// that memory allocation may **not** be async-signal-safe and thus must be
/// prevented.
///
/// Those functions are only a small subset of your operating system's API, so
/// special care must be taken to only invoke code you can control and audit.
///
/// [async-signal-safe]: https://man7.org/linux/man-pages/man7/signal-safety.7.html
#[inline]
pub unsafe fn fork() -> Result<ForkResult> {
    use self::ForkResult::*;
    let res = unsafe { libc::fork() };

    Errno::result(res).map(|res| match res {
        0 => Child,
        res => Parent { child: Pid(res) },
    })
}

/// Get the pid of this process (see
/// [getpid(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/getpid.html)).
///
/// Since you are running code, there is always a pid to return, so there
/// is no error case that needs to be handled.
#[inline]
pub fn getpid() -> Pid {
    Pid(unsafe { libc::getpid() })
}

/// Get the pid of this processes' parent (see
/// [getpid(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/getppid.html)).
///
/// There is always a parent pid to return, so there is no error case that needs
/// to be handled.
#[inline]
pub fn getppid() -> Pid {
    Pid(unsafe { libc::getppid() }) // no error handling, according to man page: "These functions are always successful."
}

/// Set a process group ID (see
/// [setpgid(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/setpgid.html)).
///
/// Set the process group id (PGID) of a particular process.  If a pid of zero
/// is specified, then the pid of the calling process is used.  Process groups
/// may be used to group together a set of processes in order for the OS to
/// apply some operations across the group.
///
/// `setsid()` may be used to create a new process group.
#[inline]
pub fn setpgid(pid: Pid, pgid: Pid) -> Result<()> {
    let res = unsafe { libc::setpgid(pid.into(), pgid.into()) };
    Errno::result(res).map(drop)
}
/// Get process group
///
/// See Also [`getpgid`](https://pubs.opengroup.org/onlinepubs/9699919799/functions/getpgid.html)
#[inline]
pub fn getpgid(pid: Option<Pid>) -> Result<Pid> {
    let res = unsafe { libc::getpgid(pid.unwrap_or(Pid(0)).into()) };
    Errno::result(res).map(Pid)
}

/// Create new session and set process group id (see
/// [setsid(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/setsid.html)).
#[inline]
pub fn setsid() -> Result<Pid> {
    Errno::result(unsafe { libc::setsid() }).map(Pid)
}

/// Get the process group ID of a session leader
/// [getsid(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/getsid.html).
///
/// Obtain the process group ID of the process that is the session leader of the process specified
/// by pid. If pid is zero, it specifies the calling process.
#[inline]
#[cfg(not(target_os = "redox"))]
pub fn getsid(pid: Option<Pid>) -> Result<Pid> {
    let res = unsafe { libc::getsid(pid.unwrap_or(Pid(0)).into()) };
    Errno::result(res).map(Pid)
}
}

feature! {
#![all(feature = "process", feature = "term")]
/// Get the terminal foreground process group (see
/// [tcgetpgrp(3)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/tcgetpgrp.html)).
///
/// Get the group process id (GPID) of the foreground process group on the
/// terminal associated to file descriptor (FD).
#[inline]
pub fn tcgetpgrp<F: AsFd>(fd: F) -> Result<Pid> {
    let res = unsafe { libc::tcgetpgrp(fd.as_fd().as_raw_fd()) };
    Errno::result(res).map(Pid)
}
/// Set the terminal foreground process group (see
/// [tcgetpgrp(3)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/tcsetpgrp.html)).
///
/// Get the group process id (PGID) to the foreground process group on the
/// terminal associated to file descriptor (FD).
#[inline]
pub fn tcsetpgrp<F: AsFd>(fd: F, pgrp: Pid) -> Result<()> {
    let res = unsafe { libc::tcsetpgrp(fd.as_fd().as_raw_fd(), pgrp.into()) };
    Errno::result(res).map(drop)
}
}

feature! {
#![feature = "process"]
/// Get the group id of the calling process (see
///[getpgrp(3)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/getpgrp.html)).
///
/// Get the process group id (PGID) of the calling process.
/// According to the man page it is always successful.
#[inline]
pub fn getpgrp() -> Pid {
    Pid(unsafe { libc::getpgrp() })
}

/// Get the caller's thread ID (see
/// [gettid(2)](https://man7.org/linux/man-pages/man2/gettid.2.html).
///
/// This function is only available on Linux based systems.  In a single
/// threaded process, the main thread will have the same ID as the process.  In
/// a multithreaded process, each thread will have a unique thread id but the
/// same process ID.
///
/// No error handling is required as a thread id should always exist for any
/// process, even if threads are not being used.
#[cfg(linux_android)]
#[inline]
pub fn gettid() -> Pid {
    Pid(unsafe { libc::syscall(libc::SYS_gettid) as pid_t })
}
}

feature! {
#![feature = "fs"]
/// Create a copy of the specified file descriptor (see
/// [dup(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/dup.html)).
///
/// The new file descriptor will have a new index but refer to the same
/// resource as the old file descriptor and the old and new file descriptors may
/// be used interchangeably.  The new and old file descriptor share the same
/// underlying resource, offset, and file status flags.  The actual index used
/// for the file descriptor will be the lowest fd index that is available.
///
/// The two file descriptors do not share file descriptor flags (e.g. `OFlag::FD_CLOEXEC`).
#[inline]
pub fn dup(oldfd: RawFd) -> Result<RawFd> {
    let res = unsafe { libc::dup(oldfd) };

    Errno::result(res)
}

/// Create a copy of the specified file descriptor using the specified fd (see
/// [dup(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/dup.html)).
///
/// This function behaves similar to `dup()` except that it will try to use the
/// specified fd instead of allocating a new one.  See the man pages for more
/// detail on the exact behavior of this function.
#[inline]
pub fn dup2(oldfd: RawFd, newfd: RawFd) -> Result<RawFd> {
    let res = unsafe { libc::dup2(oldfd, newfd) };

    Errno::result(res)
}

/// Create a new copy of the specified file descriptor using the specified fd
/// and flags (see [`dup(2)`](https://man7.org/linux/man-pages/man2/dup.2.html)).
///
/// This function behaves similar to `dup2()` but allows for flags to be
/// specified.
#[cfg(any(
    netbsdlike,
    solarish,
    target_os = "freebsd",
    target_os = "fuchsia",
    target_os = "hurd",
    target_os = "linux"
))]
pub fn dup3(oldfd: RawFd, newfd: RawFd, flags: OFlag) -> Result<RawFd> {
    let res = unsafe { libc::dup3(oldfd, newfd, flags.bits()) };

    Errno::result(res)
}

/// Change the current working directory of the calling process (see
/// [chdir(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/chdir.html)).
///
/// This function may fail in a number of different scenarios.  See the man
/// pages for additional details on possible failure cases.
#[inline]
pub fn chdir<P: ?Sized + NixPath>(path: &P) -> Result<()> {
    let res =
        path.with_nix_path(|cstr| unsafe { libc::chdir(cstr.as_ptr()) })?;

    Errno::result(res).map(drop)
}

/// Change the current working directory of the process to the one
/// given as an open file descriptor (see
/// [fchdir(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/fchdir.html)).
///
/// This function may fail in a number of different scenarios.  See the man
/// pages for additional details on possible failure cases.
#[inline]
#[cfg(not(target_os = "fuchsia"))]
pub fn fchdir(dirfd: RawFd) -> Result<()> {
    let res = unsafe { libc::fchdir(dirfd) };

    Errno::result(res).map(drop)
}

/// Creates new directory `path` with access rights `mode`.  (see [mkdir(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/mkdir.html))
///
/// # Errors
///
/// There are several situations where mkdir might fail:
///
/// - current user has insufficient rights in the parent directory
/// - the path already exists
/// - the path name is too long (longer than `PATH_MAX`, usually 4096 on linux, 1024 on OS X)
///
/// # Example
///
/// ```rust
/// use nix::unistd;
/// use nix::sys::stat;
/// use tempfile::tempdir;
///
/// let tmp_dir1 = tempdir().unwrap();
/// let tmp_dir2 = tmp_dir1.path().join("new_dir");
///
/// // create new directory and give read, write and execute rights to the owner
/// match unistd::mkdir(&tmp_dir2, stat::Mode::S_IRWXU) {
///    Ok(_) => println!("created {:?}", tmp_dir2),
///    Err(err) => println!("Error creating directory: {}", err),
/// }
/// ```
#[inline]
pub fn mkdir<P: ?Sized + NixPath>(path: &P, mode: Mode) -> Result<()> {
    let res = path.with_nix_path(|cstr| unsafe {
        libc::mkdir(cstr.as_ptr(), mode.bits() as mode_t)
    })?;

    Errno::result(res).map(drop)
}

/// Creates new fifo special file (named pipe) with path `path` and access rights `mode`.
///
/// # Errors
///
/// There are several situations where mkfifo might fail:
///
/// - current user has insufficient rights in the parent directory
/// - the path already exists
/// - the path name is too long (longer than `PATH_MAX`, usually 4096 on linux, 1024 on OS X)
///
/// For a full list consult
/// [posix specification](https://pubs.opengroup.org/onlinepubs/9699919799/functions/mkfifo.html)
///
/// # Example
///
/// ```rust
/// use nix::unistd;
/// use nix::sys::stat;
/// use tempfile::tempdir;
///
/// let tmp_dir = tempdir().unwrap();
/// let fifo_path = tmp_dir.path().join("foo.pipe");
///
/// // create new fifo and give read, write and execute rights to the owner
/// match unistd::mkfifo(&fifo_path, stat::Mode::S_IRWXU) {
///    Ok(_) => println!("created {:?}", fifo_path),
///    Err(err) => println!("Error creating fifo: {}", err),
/// }
/// ```
#[inline]
#[cfg(not(target_os = "redox"))] // RedoxFS does not support fifo yet
pub fn mkfifo<P: ?Sized + NixPath>(path: &P, mode: Mode) -> Result<()> {
    let res = path.with_nix_path(|cstr| unsafe {
        libc::mkfifo(cstr.as_ptr(), mode.bits() as mode_t)
    })?;

    Errno::result(res).map(drop)
}

/// Creates new fifo special file (named pipe) with path `path` and access rights `mode`.
///
/// If `dirfd` has a value, then `path` is relative to directory associated with the file descriptor.
///
/// If `dirfd` is `None`, then `path` is relative to the current working directory.
///
/// # References
///
/// [mkfifoat(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/mkfifoat.html).
// mkfifoat is not implemented in OSX or android
#[inline]
#[cfg(not(any(
    apple_targets,
    target_os = "haiku",
    target_os = "android",
    target_os = "redox"
)))]
pub fn mkfifoat<P: ?Sized + NixPath>(
    dirfd: Option<RawFd>,
    path: &P,
    mode: Mode,
) -> Result<()> {
    let res = path.with_nix_path(|cstr| unsafe {
        libc::mkfifoat(at_rawfd(dirfd), cstr.as_ptr(), mode.bits() as mode_t)
    })?;

    Errno::result(res).map(drop)
}

/// Creates a symbolic link at `path2` which points to `path1`.
///
/// If `dirfd` has a value, then `path2` is relative to directory associated
/// with the file descriptor.
///
/// If `dirfd` is `None`, then `path2` is relative to the current working
/// directory. This is identical to `libc::symlink(path1, path2)`.
///
/// See also [symlinkat(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/symlinkat.html).
#[cfg(not(target_os = "redox"))]
pub fn symlinkat<P1: ?Sized + NixPath, P2: ?Sized + NixPath>(
    path1: &P1,
    dirfd: Option<RawFd>,
    path2: &P2,
) -> Result<()> {
    let res = path1.with_nix_path(|path1| {
        path2.with_nix_path(|path2| unsafe {
            libc::symlinkat(
                path1.as_ptr(),
                dirfd.unwrap_or(libc::AT_FDCWD),
                path2.as_ptr(),
            )
        })
    })??;
    Errno::result(res).map(drop)
}
}

// Double the buffer capacity up to limit. In case it already has
// reached the limit, return Errno::ERANGE.
#[cfg(any(feature = "fs", feature = "user"))]
fn reserve_double_buffer_size<T>(buf: &mut Vec<T>, limit: usize) -> Result<()> {
    use std::cmp::min;

    if buf.capacity() >= limit {
        return Err(Errno::ERANGE);
    }

    let capacity = min(buf.capacity() * 2, limit);
    buf.reserve(capacity);

    Ok(())
}

feature! {
#![feature = "fs"]

/// Returns the current directory as a `PathBuf`
///
/// Err is returned if the current user doesn't have the permission to read or search a component
/// of the current path.
///
/// # Example
///
/// ```rust
/// use nix::unistd;
///
/// // assume that we are allowed to get current directory
/// let dir = unistd::getcwd().unwrap();
/// println!("The current directory is {:?}", dir);
/// ```
#[inline]
pub fn getcwd() -> Result<PathBuf> {
    let mut buf = Vec::<u8>::with_capacity(512);
    loop {
        unsafe {
            let ptr = buf.as_mut_ptr().cast();

            // The buffer must be large enough to store the absolute pathname plus
            // a terminating null byte, or else null is returned.
            // To safely handle this we start with a reasonable size (512 bytes)
            // and double the buffer size upon every error
            if !libc::getcwd(ptr, buf.capacity()).is_null() {
                let len = CStr::from_ptr(buf.as_ptr().cast())
                    .to_bytes()
                    .len();
                buf.set_len(len);
                buf.shrink_to_fit();
                return Ok(PathBuf::from(OsString::from_vec(buf)));
            } else {
                let error = Errno::last();
                // ERANGE means buffer was too small to store directory name
                if error != Errno::ERANGE {
                    return Err(error);
                }
            }

            #[cfg(not(target_os = "hurd"))]
            const PATH_MAX: usize = libc::PATH_MAX as usize;
            #[cfg(target_os = "hurd")]
            const PATH_MAX: usize = 1024; // Hurd does not define a hard limit, so try a guess first

            // Trigger the internal buffer resizing logic.
            reserve_double_buffer_size(&mut buf, PATH_MAX)?;
        }
    }
}
}

feature! {
#![all(feature = "user", feature = "fs")]

/// Computes the raw UID and GID values to pass to a `*chown` call.
// The cast is not unnecessary on all platforms.
#[allow(clippy::unnecessary_cast)]
fn chown_raw_ids(owner: Option<Uid>, group: Option<Gid>) -> (uid_t, gid_t) {
    // According to the POSIX specification, -1 is used to indicate that owner and group
    // are not to be changed.  Since uid_t and gid_t are unsigned types, we have to wrap
    // around to get -1.
    let uid = owner
        .map(Into::into)
        .unwrap_or_else(|| (0 as uid_t).wrapping_sub(1));
    let gid = group
        .map(Into::into)
        .unwrap_or_else(|| (0 as gid_t).wrapping_sub(1));
    (uid, gid)
}

/// Change the ownership of the file at `path` to be owned by the specified
/// `owner` (user) and `group` (see
/// [chown(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/chown.html)).
///
/// The owner/group for the provided path name will not be modified if `None` is
/// provided for that argument.  Ownership change will be attempted for the path
/// only if `Some` owner/group is provided.
#[inline]
pub fn chown<P: ?Sized + NixPath>(
    path: &P,
    owner: Option<Uid>,
    group: Option<Gid>,
) -> Result<()> {
    let res = path.with_nix_path(|cstr| {
        let (uid, gid) = chown_raw_ids(owner, group);
        unsafe { libc::chown(cstr.as_ptr(), uid, gid) }
    })?;

    Errno::result(res).map(drop)
}

/// Change the ownership of the file referred to by the open file descriptor `fd` to be owned by
/// the specified `owner` (user) and `group` (see
/// [fchown(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/fchown.html)).
///
/// The owner/group for the provided file will not be modified if `None` is
/// provided for that argument.  Ownership change will be attempted for the path
/// only if `Some` owner/group is provided.
#[inline]
pub fn fchown(fd: RawFd, owner: Option<Uid>, group: Option<Gid>) -> Result<()> {
    let (uid, gid) = chown_raw_ids(owner, group);
    let res = unsafe { libc::fchown(fd, uid, gid) };
    Errno::result(res).map(drop)
}

// Just a wrapper around `AtFlags` so that we can help our users migrate.
#[allow(missing_docs)]
#[cfg(not(target_os = "redox"))]
pub type FchownatFlags = AtFlags;
#[allow(missing_docs)]
#[cfg(not(target_os = "redox"))]
impl FchownatFlags {
    #[deprecated(since = "0.28.0", note = "The variant is deprecated, please use `AtFlags` instead")]
    #[allow(non_upper_case_globals)]
    pub const FollowSymlink: FchownatFlags = FchownatFlags::empty();
    #[deprecated(since = "0.28.0", note = "The variant is deprecated, please use `AtFlags` instead")]
    #[allow(non_upper_case_globals)]
    pub const NoFollowSymlink: FchownatFlags = FchownatFlags::AT_SYMLINK_NOFOLLOW;
}

/// Change the ownership of the file at `path` to be owned by the specified
/// `owner` (user) and `group`.
///
/// The owner/group for the provided path name will not be modified if `None` is
/// provided for that argument.  Ownership change will be attempted for the path
/// only if `Some` owner/group is provided.
///
/// The file to be changed is determined relative to the directory associated
/// with the file descriptor `dirfd` or the current working directory
/// if `dirfd` is `None`.
///
/// If `flag` is `AtFlags::AT_SYMLINK_NOFOLLOW` and `path` names a symbolic link,
/// then the mode of the symbolic link is changed.
///
/// `fchownat(None, path, owner, group, AtFlags::AT_SYMLINK_NOFOLLOW)` is identical to
/// a call `libc::lchown(path, owner, group)`.  That's why `lchown` is unimplemented in
/// the `nix` crate.
///
/// # References
///
/// [fchownat(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/fchownat.html).
#[cfg(not(target_os = "redox"))]
pub fn fchownat<P: ?Sized + NixPath>(
    dirfd: Option<RawFd>,
    path: &P,
    owner: Option<Uid>,
    group: Option<Gid>,
    flag: AtFlags,
) -> Result<()> {
    let res = path.with_nix_path(|cstr| unsafe {
        let (uid, gid) = chown_raw_ids(owner, group);
        libc::fchownat(
            at_rawfd(dirfd),
            cstr.as_ptr(),
            uid,
            gid,
            flag.bits()
        )
    })?;

    Errno::result(res).map(drop)
}
}

feature! {
#![feature = "process"]
fn to_exec_array<S: AsRef<CStr>>(args: &[S]) -> Vec<*const c_char> {
    use std::iter::once;
    args.iter()
        .map(|s| s.as_ref().as_ptr())
        .chain(once(ptr::null()))
        .collect()
}

/// Replace the current process image with a new one (see
/// [exec(3)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/exec.html)).
///
/// See the `::nix::unistd::execve` system call for additional details.  `execv`
/// performs the same action but does not allow for customization of the
/// environment for the new process.
#[inline]
pub fn execv<S: AsRef<CStr>>(path: &CStr, argv: &[S]) -> Result<Infallible> {
    let args_p = to_exec_array(argv);

    unsafe { libc::execv(path.as_ptr(), args_p.as_ptr()) };

    Err(Errno::last())
}

/// Replace the current process image with a new one (see
/// [execve(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/exec.html)).
///
/// The execve system call allows for another process to be "called" which will
/// replace the current process image.  That is, this process becomes the new
/// command that is run. On success, this function will not return. Instead,
/// the new program will run until it exits.
///
/// `::nix::unistd::execv` and `::nix::unistd::execve` take as arguments a slice
/// of `::std::ffi::CString`s for `args` and `env` (for `execve`). Each element
/// in the `args` list is an argument to the new process. Each element in the
/// `env` list should be a string in the form "key=value".
#[inline]
pub fn execve<SA: AsRef<CStr>, SE: AsRef<CStr>>(
    path: &CStr,
    args: &[SA],
    env: &[SE],
) -> Result<Infallible> {
    let args_p = to_exec_array(args);
    let env_p = to_exec_array(env);

    unsafe { libc::execve(path.as_ptr(), args_p.as_ptr(), env_p.as_ptr()) };

    Err(Errno::last())
}

/// Replace the current process image with a new one and replicate shell `PATH`
/// searching behavior (see
/// [exec(3)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/exec.html)).
///
/// See `::nix::unistd::execve` for additional details.  `execvp` behaves the
/// same as execv except that it will examine the `PATH` environment variables
/// for file names not specified with a leading slash.  For example, `execv`
/// would not work if "bash" was specified for the path argument, but `execvp`
/// would assuming that a bash executable was on the system `PATH`.
#[inline]
pub fn execvp<S: AsRef<CStr>>(
    filename: &CStr,
    args: &[S],
) -> Result<Infallible> {
    let args_p = to_exec_array(args);

    unsafe { libc::execvp(filename.as_ptr(), args_p.as_ptr()) };

    Err(Errno::last())
}

/// Replace the current process image with a new one and replicate shell `PATH`
/// searching behavior (see
/// [`execvpe(3)`](https://man7.org/linux/man-pages/man3/exec.3.html)).
///
/// This functions like a combination of `execvp(2)` and `execve(2)` to pass an
/// environment and have a search path. See these two for additional
/// information.
#[cfg(any(target_os = "haiku", target_os = "hurd", target_os = "linux", target_os = "openbsd"))]
pub fn execvpe<SA: AsRef<CStr>, SE: AsRef<CStr>>(
    filename: &CStr,
    args: &[SA],
    env: &[SE],
) -> Result<Infallible> {
    let args_p = to_exec_array(args);
    let env_p = to_exec_array(env);

    unsafe {
        libc::execvpe(filename.as_ptr(), args_p.as_ptr(), env_p.as_ptr())
    };

    Err(Errno::last())
}

/// Replace the current process image with a new one (see
/// [fexecve(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/fexecve.html)).
///
/// The `fexecve` function allows for another process to be "called" which will
/// replace the current process image.  That is, this process becomes the new
/// command that is run. On success, this function will not return. Instead,
/// the new program will run until it exits.
///
/// This function is similar to `execve`, except that the program to be executed
/// is referenced as a file descriptor instead of a path.
#[cfg(any(linux_android, freebsdlike, target_os = "hurd"))]
#[inline]
pub fn fexecve<SA: AsRef<CStr>, SE: AsRef<CStr>>(
    fd: RawFd,
    args: &[SA],
    env: &[SE],
) -> Result<Infallible> {
    let args_p = to_exec_array(args);
    let env_p = to_exec_array(env);

    unsafe { libc::fexecve(fd, args_p.as_ptr(), env_p.as_ptr()) };

    Err(Errno::last())
}

/// Execute program relative to a directory file descriptor (see
/// [execveat(2)](https://man7.org/linux/man-pages/man2/execveat.2.html)).
///
/// The `execveat` function allows for another process to be "called" which will
/// replace the current process image.  That is, this process becomes the new
/// command that is run. On success, this function will not return. Instead,
/// the new program will run until it exits.
///
/// This function is similar to `execve`, except that the program to be executed
/// is referenced as a file descriptor to the base directory plus a path.
#[cfg(linux_android)]
#[inline]
pub fn execveat<SA: AsRef<CStr>, SE: AsRef<CStr>>(
    dirfd: Option<RawFd>,
    pathname: &CStr,
    args: &[SA],
    env: &[SE],
    flags: super::fcntl::AtFlags,
) -> Result<Infallible> {
    let dirfd = at_rawfd(dirfd);
    let args_p = to_exec_array(args);
    let env_p = to_exec_array(env);

    unsafe {
        libc::syscall(
            libc::SYS_execveat,
            dirfd,
            pathname.as_ptr(),
            args_p.as_ptr(),
            env_p.as_ptr(),
            flags,
        );
    };

    Err(Errno::last())
}

/// Daemonize this process by detaching from the controlling terminal (see
/// [daemon(3)](https://man7.org/linux/man-pages/man3/daemon.3.html)).
///
/// When a process is launched it is typically associated with a parent and it,
/// in turn, by its controlling terminal/process.  In order for a process to run
/// in the "background" it must daemonize itself by detaching itself.  Under
/// posix, this is done by doing the following:
///
/// 1. Parent process (this one) forks
/// 2. Parent process exits
/// 3. Child process continues to run.
///
/// `nochdir`:
///
/// * `nochdir = true`: The current working directory after daemonizing will
///    be the current working directory.
/// *  `nochdir = false`: The current working directory after daemonizing will
///    be the root direcory, `/`.
///
/// `noclose`:
///
/// * `noclose = true`: The process' current stdin, stdout, and stderr file
///   descriptors will remain identical after daemonizing.
/// * `noclose = false`: The process' stdin, stdout, and stderr will point to
///   `/dev/null` after daemonizing.
#[cfg(any(
        linux_android,
        freebsdlike,
        solarish,
        netbsdlike
))]
pub fn daemon(nochdir: bool, noclose: bool) -> Result<()> {
    let res = unsafe { libc::daemon(nochdir as c_int, noclose as c_int) };
    Errno::result(res).map(drop)
}
}

feature! {
#![feature = "hostname"]

/// Set the system host name (see
/// [sethostname(2)](https://man7.org/linux/man-pages/man2/gethostname.2.html)).
///
/// Given a name, attempt to update the system host name to the given string.
/// On some systems, the host name is limited to as few as 64 bytes.  An error
/// will be returned if the name is not valid or the current process does not
/// have permissions to update the host name.
#[cfg(not(target_os = "redox"))]
pub fn sethostname<S: AsRef<OsStr>>(name: S) -> Result<()> {
    // Handle some differences in type of the len arg across platforms.
    cfg_if! {
        if #[cfg(any(freebsdlike,
                     solarish,
                     apple_targets,
                     target_os = "aix"))] {
            type sethostname_len_t = c_int;
        } else {
            type sethostname_len_t = size_t;
        }
    }
    let ptr = name.as_ref().as_bytes().as_ptr().cast();
    let len = name.as_ref().len() as sethostname_len_t;

    let res = unsafe { libc::sethostname(ptr, len) };
    Errno::result(res).map(drop)
}

/// Get the host name and store it in an internally allocated buffer, returning an
/// `OsString` on success (see
/// [gethostname(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/gethostname.html)).
///
/// This function call attempts to get the host name for the running system and
/// store it in an internal buffer, returning it as an `OsString` if successful.
///
/// ```no_run
/// use nix::unistd;
///
/// let hostname = unistd::gethostname().expect("Failed getting hostname");
/// let hostname = hostname.into_string().expect("Hostname wasn't valid UTF-8");
/// println!("Hostname: {}", hostname);
/// ```
pub fn gethostname() -> Result<OsString> {
    // The capacity is the max length of a hostname plus the NUL terminator.
    let mut buffer: Vec<u8> = Vec::with_capacity(256);
    let ptr = buffer.as_mut_ptr().cast();
    let len = buffer.capacity() as size_t;

    let res = unsafe { libc::gethostname(ptr, len) };
    Errno::result(res).map(|_| {
        unsafe {
            buffer.as_mut_ptr().wrapping_add(len - 1).write(0); // ensure always null-terminated
            let len = CStr::from_ptr(buffer.as_ptr().cast()).len();
            buffer.set_len(len);
        }
        OsString::from_vec(buffer)
    })
}
}

/// Close a raw file descriptor
///
/// Be aware that many Rust types implicitly close-on-drop, including
/// `std::fs::File`.  Explicitly closing them with this method too can result in
/// a double-close condition, which can cause confusing `EBADF` errors in
/// seemingly unrelated code.  Caveat programmer.  See also
/// [close(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/close.html).
///
/// # Examples
///
/// ```no_run
/// use std::os::unix::io::AsRawFd;
/// use nix::unistd::close;
///
/// let f = tempfile::tempfile().unwrap();
/// close(f.as_raw_fd()).unwrap();   // Bad!  f will also close on drop!
/// ```
///
/// ```rust
/// use std::os::unix::io::IntoRawFd;
/// use nix::unistd::close;
///
/// let f = tempfile::tempfile().unwrap();
/// close(f.into_raw_fd()).unwrap(); // Good.  into_raw_fd consumes f
/// ```
pub fn close(fd: RawFd) -> Result<()> {
    let res = unsafe { libc::close(fd) };
    Errno::result(res).map(drop)
}

/// Read from a raw file descriptor.
///
/// See also [read(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/read.html)
pub fn read(fd: RawFd, buf: &mut [u8]) -> Result<usize> {
    let res =
        unsafe { libc::read(fd, buf.as_mut_ptr().cast(), buf.len() as size_t) };

    Errno::result(res).map(|r| r as usize)
}

/// Write to a raw file descriptor.
///
/// See also [write(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/write.html)
pub fn write<Fd: AsFd>(fd: Fd, buf: &[u8]) -> Result<usize> {
    let res = unsafe {
        libc::write(
            fd.as_fd().as_raw_fd(),
            buf.as_ptr().cast(),
            buf.len() as size_t,
        )
    };

    Errno::result(res).map(|r| r as usize)
}

feature! {
#![feature = "fs"]

/// Directive that tells [`lseek`] and [`lseek64`] what the offset is relative to.
///
/// [`lseek`]: ./fn.lseek.html
/// [`lseek64`]: ./fn.lseek64.html
#[repr(i32)]
#[derive(Clone, Copy, Debug)]
pub enum Whence {
    /// Specify an offset relative to the start of the file.
    SeekSet = libc::SEEK_SET,
    /// Specify an offset relative to the current file location.
    SeekCur = libc::SEEK_CUR,
    /// Specify an offset relative to the end of the file.
    SeekEnd = libc::SEEK_END,
    /// Specify an offset relative to the next location in the file greater than or
    /// equal to offset that contains some data. If offset points to
    /// some data, then the file offset is set to offset.
    #[cfg(any(
        freebsdlike,
        solarish,
        target_os = "linux",
    ))]
    SeekData = libc::SEEK_DATA,
    /// Specify an offset relative to the next hole in the file greater than
    /// or equal to offset. If offset points into the middle of a hole, then
    /// the file offset should be set to offset. If there is no hole past offset,
    /// then the file offset should be adjusted to the end of the file (i.e., there
    /// is an implicit hole at the end of any file).
    #[cfg(any(
        freebsdlike,
        solarish,
        target_os = "linux",
    ))]
    SeekHole = libc::SEEK_HOLE,
}

/// Move the read/write file offset.
///
/// See also [lseek(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/lseek.html)
pub fn lseek(fd: RawFd, offset: off_t, whence: Whence) -> Result<off_t> {
    let res = unsafe { libc::lseek(fd, offset, whence as i32) };

    Errno::result(res).map(|r| r as off_t)
}

/// Move the read/write file offset.
///
/// Unlike [`lseek`], it takes a 64-bit argument even on platforms where [`libc::off_t`] is
/// 32 bits.
#[cfg(linux_android)]
pub fn lseek64(
    fd: RawFd,
    offset: libc::off64_t,
    whence: Whence,
) -> Result<libc::off64_t> {
    let res = unsafe { libc::lseek64(fd, offset, whence as i32) };

    Errno::result(res).map(|r| r as libc::off64_t)
}
}

/// Create an interprocess channel.
///
/// See also [pipe(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/pipe.html)
pub fn pipe() -> std::result::Result<(OwnedFd, OwnedFd), Error> {
    let mut fds = mem::MaybeUninit::<[OwnedFd; 2]>::uninit();

    let res = unsafe { libc::pipe(fds.as_mut_ptr().cast()) };

    Error::result(res)?;

    let [read, write] = unsafe { fds.assume_init() };
    Ok((read, write))
}

feature! {
#![feature = "fs"]
/// Like `pipe`, but allows setting certain file descriptor flags.
///
/// The following flags are supported, and will be set atomically as the pipe is
/// created:
///
/// - `O_CLOEXEC`:    Set the close-on-exec flag for the new file descriptors.
#[cfg_attr(
    target_os = "linux",
    doc = "- `O_DIRECT`: Create a pipe that performs I/O in \"packet\" mode."
)]
#[cfg_attr(
    target_os = "netbsd",
    doc = "- `O_NOSIGPIPE`: Return `EPIPE` instead of raising `SIGPIPE`."
)]
/// - `O_NONBLOCK`:   Set the non-blocking flag for the ends of the pipe.
///
/// See also [pipe(2)](https://man7.org/linux/man-pages/man2/pipe.2.html)
#[cfg(any(
    linux_android,
    freebsdlike,
    solarish,
    target_os = "emscripten",
    target_os = "hurd",
    target_os = "redox",
    netbsdlike,
))]
pub fn pipe2(flags: OFlag) -> Result<(OwnedFd, OwnedFd)> {
    let mut fds = mem::MaybeUninit::<[OwnedFd; 2]>::uninit();

    let res =
        unsafe { libc::pipe2(fds.as_mut_ptr().cast(), flags.bits()) };

    Errno::result(res)?;

    let [read, write] = unsafe { fds.assume_init() };
    Ok((read, write))
}

/// Truncate a file to a specified length
///
/// See also
/// [truncate(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/truncate.html)
#[cfg(not(any(target_os = "redox", target_os = "fuchsia")))]
pub fn truncate<P: ?Sized + NixPath>(path: &P, len: off_t) -> Result<()> {
    let res = path
        .with_nix_path(|cstr| unsafe { libc::truncate(cstr.as_ptr(), len) })?;

    Errno::result(res).map(drop)
}

/// Truncate a file to a specified length
///
/// See also
/// [ftruncate(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/ftruncate.html)
pub fn ftruncate<Fd: AsFd>(fd: Fd, len: off_t) -> Result<()> {
    Errno::result(unsafe { libc::ftruncate(fd.as_fd().as_raw_fd(), len) }).map(drop)
}

/// Determines if the file descriptor refers to a valid terminal type device.
pub fn isatty(fd: RawFd) -> Result<bool> {
    unsafe {
        // ENOTTY means `fd` is a valid file descriptor, but not a TTY, so
        // we return `Ok(false)`
        if libc::isatty(fd) == 1 {
            Ok(true)
        } else {
            match Errno::last() {
                Errno::ENOTTY => Ok(false),
                err => Err(err),
            }
        }
    }
}

#[allow(missing_docs)]
#[cfg(not(target_os = "redox"))]
pub type LinkatFlags = AtFlags;
#[allow(missing_docs)]
#[cfg(not(target_os = "redox"))]
impl LinkatFlags {
    #[deprecated(since = "0.28.0", note = "The variant is deprecated, please use `AtFlags` instead")]
    #[allow(non_upper_case_globals)]
    pub const SymlinkFollow: LinkatFlags = LinkatFlags::AT_SYMLINK_FOLLOW;
    #[deprecated(since = "0.28.0", note = "The variant is deprecated, please use `AtFlags` instead")]
    #[allow(non_upper_case_globals)]
    pub const NoSymlinkFollow: LinkatFlags = LinkatFlags::empty();
}

/// Link one file to another file
///
/// Creates a new link (directory entry) at `newpath` for the existing file at `oldpath`. In the
/// case of a relative `oldpath`, the path is interpreted relative to the directory associated
/// with file descriptor `olddirfd` instead of the current working directory and similiarly for
/// `newpath` and file descriptor `newdirfd`. In case `flag` is `AtFlags::AT_SYMLINK_FOLLOW` and
/// `oldpath` names a symoblic link, a new link for the target of the symbolic link is created.
/// If either `olddirfd` or `newdirfd` is `None`, `AT_FDCWD` is used respectively where `oldpath`
/// and/or `newpath` is then interpreted relative to the current working directory of the calling
/// process. If either `oldpath` or `newpath` is absolute, then `dirfd` is ignored.
///
/// # References
/// See also [linkat(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/linkat.html)
#[cfg(not(target_os = "redox"))] // RedoxFS does not support symlinks yet
pub fn linkat<P: ?Sized + NixPath>(
    olddirfd: Option<RawFd>,
    oldpath: &P,
    newdirfd: Option<RawFd>,
    newpath: &P,
    flag: AtFlags,
) -> Result<()> {
    let res = oldpath.with_nix_path(|oldcstr| {
        newpath.with_nix_path(|newcstr| unsafe {
            libc::linkat(
                at_rawfd(olddirfd),
                oldcstr.as_ptr(),
                at_rawfd(newdirfd),
                newcstr.as_ptr(),
                flag.bits(),
            )
        })
    })??;
    Errno::result(res).map(drop)
}

/// Remove a directory entry
///
/// See also [unlink(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/unlink.html)
pub fn unlink<P: ?Sized + NixPath>(path: &P) -> Result<()> {
    let res =
        path.with_nix_path(|cstr| unsafe { libc::unlink(cstr.as_ptr()) })?;
    Errno::result(res).map(drop)
}

/// Flags for `unlinkat` function.
#[derive(Clone, Copy, Debug)]
pub enum UnlinkatFlags {
    /// Remove the directory entry as a directory, not a normal file
    RemoveDir,
    /// Remove the directory entry as a normal file, not a directory
    NoRemoveDir,
}

/// Remove a directory entry
///
/// In the case of a relative path, the directory entry to be removed is determined relative to
/// the directory associated with the file descriptor `dirfd` or the current working directory
/// if `dirfd` is `None`. In the case of an absolute `path` `dirfd` is ignored. If `flag` is
/// `UnlinkatFlags::RemoveDir` then removal of the directory entry specified by `dirfd` and `path`
/// is performed.
///
/// # References
/// See also [unlinkat(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/unlinkat.html)
#[cfg(not(target_os = "redox"))]
pub fn unlinkat<P: ?Sized + NixPath>(
    dirfd: Option<RawFd>,
    path: &P,
    flag: UnlinkatFlags,
) -> Result<()> {
    let atflag = match flag {
        UnlinkatFlags::RemoveDir => AtFlags::AT_REMOVEDIR,
        UnlinkatFlags::NoRemoveDir => AtFlags::empty(),
    };
    let res = path.with_nix_path(|cstr| unsafe {
        libc::unlinkat(
            at_rawfd(dirfd),
            cstr.as_ptr(),
            atflag.bits() as libc::c_int,
        )
    })?;
    Errno::result(res).map(drop)
}

/// Change a process's root directory
#[inline]
#[cfg(not(target_os = "fuchsia"))]
pub fn chroot<P: ?Sized + NixPath>(path: &P) -> Result<()> {
    let res =
        path.with_nix_path(|cstr| unsafe { libc::chroot(cstr.as_ptr()) })?;

    Errno::result(res).map(drop)
}

/// Commit filesystem caches to disk
///
/// See also [sync(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/sync.html)
#[cfg(any(bsd, linux_android, solarish, target_os = "haiku", target_os = "aix", target_os = "hurd"))]
pub fn sync() {
    unsafe { libc::sync() };
}

/// Commit filesystem caches containing file referred to by the open file
/// descriptor `fd` to disk
///
/// See also [syncfs(2)](https://man7.org/linux/man-pages/man2/sync.2.html)
#[cfg(any(linux_android, target_os = "hurd"))]
pub fn syncfs(fd: RawFd) -> Result<()> {
    let res = unsafe { libc::syncfs(fd) };

    Errno::result(res).map(drop)
}

/// Synchronize changes to a file
///
/// See also [fsync(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/fsync.html)
#[inline]
pub fn fsync(fd: RawFd) -> Result<()> {
    let res = unsafe { libc::fsync(fd) };

    Errno::result(res).map(drop)
}

/// Synchronize the data of a file
///
/// See also
/// [fdatasync(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/fdatasync.html)
#[cfg(any(
    linux_android,
    solarish,
    netbsdlike,
    apple_targets,
    target_os = "freebsd",
    target_os = "emscripten",
    target_os = "fuchsia",
    target_os = "aix",
    target_os = "hurd",
))]
#[inline]
pub fn fdatasync(fd: RawFd) -> Result<()> {
    cfg_if! {
        // apple libc supports fdatasync too, albeit not being present in its headers
        // [fdatasync](https://github.com/apple/darwin-xnu/blob/2ff845c2e033bd0ff64b5b6aa6063a1f8f65aa32/bsd/vfs/vfs_syscalls.c#L7728)
        if #[cfg(apple_targets)] {
            extern "C" {
                fn fdatasync(fd: libc::c_int) -> libc::c_int;
            }
        } else {
            use libc::fdatasync as fdatasync;
        }
    }
    let res = unsafe { fdatasync(fd) };

    Errno::result(res).map(drop)
}
}

feature! {
#![feature = "user"]

/// Get a real user ID
///
/// See also [getuid(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/getuid.html)
// POSIX requires that getuid is always successful, so no need to check return
// value or errno.
#[inline]
pub fn getuid() -> Uid {
    Uid(unsafe { libc::getuid() })
}

/// Get the effective user ID
///
/// See also [geteuid(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/geteuid.html)
// POSIX requires that geteuid is always successful, so no need to check return
// value or errno.
#[inline]
pub fn geteuid() -> Uid {
    Uid(unsafe { libc::geteuid() })
}

/// Get the real group ID
///
/// See also [getgid(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/getgid.html)
// POSIX requires that getgid is always successful, so no need to check return
// value or errno.
#[inline]
pub fn getgid() -> Gid {
    Gid(unsafe { libc::getgid() })
}

/// Get the effective group ID
///
/// See also [getegid(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/getegid.html)
// POSIX requires that getegid is always successful, so no need to check return
// value or errno.
#[inline]
pub fn getegid() -> Gid {
    Gid(unsafe { libc::getegid() })
}

/// Set the effective user ID
///
/// See also [seteuid(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/seteuid.html)
#[inline]
pub fn seteuid(euid: Uid) -> Result<()> {
    let res = unsafe { libc::seteuid(euid.into()) };

    Errno::result(res).map(drop)
}

/// Set the effective group ID
///
/// See also [setegid(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/setegid.html)
#[inline]
pub fn setegid(egid: Gid) -> Result<()> {
    let res = unsafe { libc::setegid(egid.into()) };

    Errno::result(res).map(drop)
}

/// Set the user ID
///
/// See also [setuid(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/setuid.html)
#[inline]
pub fn setuid(uid: Uid) -> Result<()> {
    let res = unsafe { libc::setuid(uid.into()) };

    Errno::result(res).map(drop)
}

/// Set the group ID
///
/// See also [setgid(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/setgid.html)
#[inline]
pub fn setgid(gid: Gid) -> Result<()> {
    let res = unsafe { libc::setgid(gid.into()) };

    Errno::result(res).map(drop)
}
}

feature! {
#![all(feature = "fs", feature = "user")]
/// Set the user identity used for filesystem checks per-thread.
/// On both success and failure, this call returns the previous filesystem user
/// ID of the caller.
///
/// See also [setfsuid(2)](https://man7.org/linux/man-pages/man2/setfsuid.2.html)
#[cfg(linux_android)]
pub fn setfsuid(uid: Uid) -> Uid {
    let prev_fsuid = unsafe { libc::setfsuid(uid.into()) };
    Uid::from_raw(prev_fsuid as uid_t)
}

/// Set the group identity used for filesystem checks per-thread.
/// On both success and failure, this call returns the previous filesystem group
/// ID of the caller.
///
/// See also [setfsgid(2)](https://man7.org/linux/man-pages/man2/setfsgid.2.html)
#[cfg(linux_android)]
pub fn setfsgid(gid: Gid) -> Gid {
    let prev_fsgid = unsafe { libc::setfsgid(gid.into()) };
    Gid::from_raw(prev_fsgid as gid_t)
}
}

feature! {
#![feature = "user"]

/// Get the list of supplementary group IDs of the calling process.
///
/// [Further reading](https://pubs.opengroup.org/onlinepubs/009695399/functions/getgroups.html)
///
/// **Note:** This function is not available for Apple platforms. On those
/// platforms, checking group membership should be achieved via communication
/// with the `opendirectoryd` service.
#[cfg(not(apple_targets))]
pub fn getgroups() -> Result<Vec<Gid>> {
    // First get the maximum number of groups. The value returned
    // shall always be greater than or equal to one and less than or
    // equal to the value of {NGROUPS_MAX} + 1.
    let ngroups_max = match sysconf(SysconfVar::NGROUPS_MAX) {
        Ok(Some(n)) => (n + 1) as usize,
        Ok(None) | Err(_) => usize::MAX,
    };

    // Next, get the number of groups so we can size our Vec
    let ngroups = unsafe { libc::getgroups(0, ptr::null_mut()) };

    // If there are no supplementary groups, return early.
    // This prevents a potential buffer over-read if the number of groups
    // increases from zero before the next call. It would return the total
    // number of groups beyond the capacity of the buffer.
    if ngroups == 0 {
        return Ok(Vec::new());
    }

    // Now actually get the groups. We try multiple times in case the number of
    // groups has changed since the first call to getgroups() and the buffer is
    // now too small.
    let mut groups =
        Vec::<Gid>::with_capacity(Errno::result(ngroups)? as usize);
    loop {
        // FIXME: On the platforms we currently support, the `Gid` struct has
        // the same representation in memory as a bare `gid_t`. This is not
        // necessarily the case on all Rust platforms, though. See RFC 1785.
        let ngroups = unsafe {
            libc::getgroups(
                groups.capacity() as c_int,
                groups.as_mut_ptr().cast(),
            )
        };

        match Errno::result(ngroups) {
            Ok(s) => {
                unsafe { groups.set_len(s as usize) };
                return Ok(groups);
            }
            Err(Errno::EINVAL) => {
                // EINVAL indicates that the buffer size was too
                // small, resize it up to ngroups_max as limit.
                reserve_double_buffer_size(&mut groups, ngroups_max)
                    .or(Err(Errno::EINVAL))?;
            }
            Err(e) => return Err(e),
        }
    }
}

/// Set the list of supplementary group IDs for the calling process.
///
/// [Further reading](https://man7.org/linux/man-pages/man2/getgroups.2.html)
///
/// **Note:** This function is not available for Apple platforms. On those
/// platforms, group membership management should be achieved via communication
/// with the `opendirectoryd` service.
///
/// # Examples
///
/// `setgroups` can be used when dropping privileges from the root user to a
/// specific user and group. For example, given the user `www-data` with UID
/// `33` and the group `backup` with the GID `34`, one could switch the user as
/// follows:
///
/// ```rust,no_run
/// # use std::error::Error;
/// # use nix::unistd::*;
/// #
/// # fn try_main() -> Result<(), Box<dyn Error>> {
/// let uid = Uid::from_raw(33);
/// let gid = Gid::from_raw(34);
/// setgroups(&[gid])?;
/// setgid(gid)?;
/// setuid(uid)?;
/// #
/// #     Ok(())
/// # }
/// #
/// # try_main().unwrap();
/// ```
#[cfg(not(any(
    apple_targets,
    target_os = "redox",
    target_os = "haiku"
)))]
pub fn setgroups(groups: &[Gid]) -> Result<()> {
    cfg_if! {
        if #[cfg(any(bsd,
                     solarish,
                     target_os = "aix"))] {
            type setgroups_ngroups_t = c_int;
        } else {
            type setgroups_ngroups_t = size_t;
        }
    }
    // FIXME: On the platforms we currently support, the `Gid` struct has the
    // same representation in memory as a bare `gid_t`. This is not necessarily
    // the case on all Rust platforms, though. See RFC 1785.
    let res = unsafe {
        libc::setgroups(
            groups.len() as setgroups_ngroups_t,
            groups.as_ptr().cast(),
        )
    };

    Errno::result(res).map(drop)
}

/// Calculate the supplementary group access list.
///
/// Gets the group IDs of all groups that `user` is a member of. The additional
/// group `group` is also added to the list.
///
/// [Further reading](https://man7.org/linux/man-pages/man3/getgrouplist.3.html)
///
/// **Note:** This function is not available for Apple platforms. On those
/// platforms, checking group membership should be achieved via communication
/// with the `opendirectoryd` service.
///
/// # Errors
///
/// Although the `getgrouplist()` call does not return any specific
/// errors on any known platforms, this implementation will return a system
/// error of `EINVAL` if the number of groups to be fetched exceeds the
/// `NGROUPS_MAX` sysconf value. This mimics the behaviour of `getgroups()`
/// and `setgroups()`. Additionally, while some implementations will return a
/// partial list of groups when `NGROUPS_MAX` is exceeded, this implementation
/// will only ever return the complete list or else an error.
#[cfg(not(any(
    target_os = "aix",
    solarish,
    apple_targets,
    target_os = "redox"
)))]
pub fn getgrouplist(user: &CStr, group: Gid) -> Result<Vec<Gid>> {
    let ngroups_max = match sysconf(SysconfVar::NGROUPS_MAX) {
        Ok(Some(n)) => n as c_int,
        Ok(None) | Err(_) => c_int::MAX,
    };
    use std::cmp::min;
    let mut groups = Vec::<Gid>::with_capacity(min(ngroups_max, 8) as usize);
    cfg_if! {
        if #[cfg(apple_targets)] {
            type getgrouplist_group_t = c_int;
        } else {
            type getgrouplist_group_t = gid_t;
        }
    }
    let gid: gid_t = group.into();
    loop {
        let mut ngroups = groups.capacity() as i32;
        let ret = unsafe {
            libc::getgrouplist(
                user.as_ptr(),
                gid as getgrouplist_group_t,
                groups.as_mut_ptr().cast(),
                &mut ngroups,
            )
        };

        // BSD systems only return 0 or -1, Linux returns ngroups on success.
        if ret >= 0 {
            unsafe { groups.set_len(ngroups as usize) };
            return Ok(groups);
        } else if ret == -1 {
            // Returns -1 if ngroups is too small, but does not set errno.
            // BSD systems will still fill the groups buffer with as many
            // groups as possible, but Linux manpages do not mention this
            // behavior.
            reserve_double_buffer_size(&mut groups, ngroups_max as usize)
                .map_err(|_| Errno::EINVAL)?;
        }
    }
}

/// Initialize the supplementary group access list.
///
/// Sets the supplementary group IDs for the calling process using all groups
/// that `user` is a member of. The additional group `group` is also added to
/// the list.
///
/// [Further reading](https://man7.org/linux/man-pages/man3/initgroups.3.html)
///
/// **Note:** This function is not available for Apple platforms. On those
/// platforms, group membership management should be achieved via communication
/// with the `opendirectoryd` service.
///
/// # Examples
///
/// `initgroups` can be used when dropping privileges from the root user to
/// another user. For example, given the user `www-data`, we could look up the
/// UID and GID for the user in the system's password database (usually found
/// in `/etc/passwd`). If the `www-data` user's UID and GID were `33` and `33`,
/// respectively, one could switch the user as follows:
///
/// ```rust,no_run
/// # use std::error::Error;
/// # use std::ffi::CString;
/// # use nix::unistd::*;
/// #
/// # fn try_main() -> Result<(), Box<dyn Error>> {
/// let user = CString::new("www-data").unwrap();
/// let uid = Uid::from_raw(33);
/// let gid = Gid::from_raw(33);
/// initgroups(&user, gid)?;
/// setgid(gid)?;
/// setuid(uid)?;
/// #
/// #     Ok(())
/// # }
/// #
/// # try_main().unwrap();
/// ```
#[cfg(not(any(
    apple_targets,
    target_os = "redox",
    target_os = "haiku"
)))]
pub fn initgroups(user: &CStr, group: Gid) -> Result<()> {
    cfg_if! {
        if #[cfg(apple_targets)] {
            type initgroups_group_t = c_int;
        } else {
            type initgroups_group_t = gid_t;
        }
    }
    let gid: gid_t = group.into();
    let res =
        unsafe { libc::initgroups(user.as_ptr(), gid as initgroups_group_t) };

    Errno::result(res).map(drop)
}
}

feature! {
#![feature = "signal"]

/// Suspend the thread until a signal is received.
///
/// See also [pause(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/pause.html).
#[inline]
#[cfg(not(target_os = "redox"))]
pub fn pause() {
    unsafe { libc::pause() };
}

pub mod alarm {
    //! Alarm signal scheduling.
    //!
    //! Scheduling an alarm will trigger a `SIGALRM` signal when the time has
    //! elapsed, which has to be caught, because the default action for the
    //! signal is to terminate the program. This signal also can't be ignored
    //! because the system calls like `pause` will not be interrupted, see the
    //! second example below.
    //!
    //! # Examples
    //!
    //! Canceling an alarm:
    //!
    //! ```
    //! use nix::unistd::alarm;
    //!
    //! // Set an alarm for 60 seconds from now.
    //! alarm::set(60);
    //!
    //! // Cancel the above set alarm, which returns the number of seconds left
    //! // of the previously set alarm.
    //! assert_eq!(alarm::cancel(), Some(60));
    //! ```
    //!
    //! Scheduling an alarm and waiting for the signal:
    //!
    #![cfg_attr(target_os = "redox", doc = " ```rust,ignore")]
    #![cfg_attr(not(target_os = "redox"), doc = " ```rust")]
    //! use std::time::{Duration, Instant};
    //!
    //! use nix::unistd::{alarm, pause};
    //! use nix::sys::signal::*;
    //!
    //! // We need to setup an empty signal handler to catch the alarm signal,
    //! // otherwise the program will be terminated once the signal is delivered.
    //! extern fn signal_handler(_: nix::libc::c_int) { }
    //! let sa = SigAction::new(
    //!     SigHandler::Handler(signal_handler),
    //!     SaFlags::SA_RESTART,
    //!     SigSet::empty()
    //! );
    //! unsafe {
    //!     sigaction(Signal::SIGALRM, &sa);
    //! }
    //!
    //! let start = Instant::now();
    //!
    //! // Set an alarm for 1 second from now.
    //! alarm::set(1);
    //!
    //! // Pause the process until the alarm signal is received.
    //! let mut sigset = SigSet::empty();
    //! sigset.add(Signal::SIGALRM);
    //! sigset.wait();
    //!
    //! assert!(start.elapsed() >= Duration::from_secs(1));
    //! ```
    //!
    //! # References
    //!
    //! See also [alarm(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/alarm.html).

    /// Schedule an alarm signal.
    ///
    /// This will cause the system to generate a `SIGALRM` signal for the
    /// process after the specified number of seconds have elapsed.
    ///
    /// Returns the leftover time of a previously set alarm if there was one.
    pub fn set(secs: libc::c_uint) -> Option<libc::c_uint> {
        assert!(secs != 0, "passing 0 to `alarm::set` is not allowed, to cancel an alarm use `alarm::cancel`");
        alarm(secs)
    }

    /// Cancel an previously set alarm signal.
    ///
    /// Returns the leftover time of a previously set alarm if there was one.
    pub fn cancel() -> Option<libc::c_uint> {
        alarm(0)
    }

    fn alarm(secs: libc::c_uint) -> Option<libc::c_uint> {
        match unsafe { libc::alarm(secs) } {
            0 => None,
            secs => Some(secs),
        }
    }
}
}

/// Suspend execution for an interval of time
///
/// See also [sleep(2)](https://pubs.opengroup.org/onlinepubs/009695399/functions/sleep.html#tag_03_705_05)
// Per POSIX, does not fail
#[inline]
pub fn sleep(seconds: c_uint) -> c_uint {
    unsafe { libc::sleep(seconds) }
}

feature! {
#![feature = "acct"]

/// Process accounting
#[cfg(not(any(target_os = "redox", target_os = "haiku")))]
pub mod acct {
    use crate::errno::Errno;
    use crate::{NixPath, Result};
    use std::ptr;

    /// Enable process accounting
    ///
    /// See also [acct(2)](https://linux.die.net/man/2/acct)
    pub fn enable<P: ?Sized + NixPath>(filename: &P) -> Result<()> {
        let res = filename
            .with_nix_path(|cstr| unsafe { libc::acct(cstr.as_ptr()) })?;

        Errno::result(res).map(drop)
    }

    /// Disable process accounting
    pub fn disable() -> Result<()> {
        let res = unsafe { libc::acct(ptr::null()) };

        Errno::result(res).map(drop)
    }
}
}

feature! {
#![feature = "fs"]
/// Creates a regular file which persists even after process termination
///
/// * `template`: a path whose 6 rightmost characters must be X, e.g. `/tmp/tmpfile_XXXXXX`
/// * returns: tuple of file descriptor and filename
///
/// Err is returned either if no temporary filename could be created or the template doesn't
/// end with XXXXXX
///
/// See also [mkstemp(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/mkstemp.html)
///
/// # Example
///
/// ```rust
/// use nix::unistd;
///
/// let _ = match unistd::mkstemp("/tmp/tempfile_XXXXXX") {
///     Ok((fd, path)) => {
///         unistd::unlink(path.as_path()).unwrap(); // flag file to be deleted at app termination
///         fd
///     }
///     Err(e) => panic!("mkstemp failed: {}", e)
/// };
/// // do something with fd
/// ```
#[inline]
pub fn mkstemp<P: ?Sized + NixPath>(template: &P) -> Result<(RawFd, PathBuf)> {
    let mut path =
        template.with_nix_path(|path| path.to_bytes_with_nul().to_owned())?;
    let p = path.as_mut_ptr().cast();
    let fd = unsafe { libc::mkstemp(p) };
    let last = path.pop(); // drop the trailing nul
    debug_assert!(last == Some(b'\0'));
    let pathname = OsString::from_vec(path);
    Errno::result(fd)?;
    Ok((fd, PathBuf::from(pathname)))
}
}

feature! {
#![all(feature = "fs", feature = "feature")]

/// Creates a directory which persists even after process termination
///
/// * `template`: a path whose rightmost characters contain some number of X, e.g. `/tmp/tmpdir_XXXXXX`
/// * returns: filename
///
/// Err is returned either if no temporary filename could be created or the template had insufficient X
///
/// See also [mkstemp(2)](http://pubs.opengroup.org/onlinepubs/9699919799/functions/mkdtemp.html)
///
/// ```
/// use nix::unistd;
///
/// match unistd::mkdtemp("/tmp/tempdir_XXXXXX") {
///     Ok(_path) => {
///         // do something with directory
///     }
///     Err(e) => panic!("mkdtemp failed: {}", e)
/// };
/// ```
pub fn mkdtemp<P: ?Sized + NixPath>(template: &P) -> Result<PathBuf> {
    let mut path = template.with_nix_path(|path| {path.to_bytes_with_nul().to_owned()})?;
    let p = path.as_mut_ptr() as *mut _;
    let p = unsafe { libc::mkdtemp(p) };
    if p.is_null() {
        return Err(Errno::last());
    }
    let last = path.pop(); // drop the trailing nul
    debug_assert!(last == Some(b'\0'));
    let pathname = OsString::from_vec(path);
    Ok(PathBuf::from(pathname))
}

/// Variable names for `pathconf`
///
/// Nix uses the same naming convention for these variables as the
/// [getconf(1)](https://pubs.opengroup.org/onlinepubs/9699919799/utilities/getconf.html) utility.
/// That is, `PathconfVar` variables have the same name as the abstract
/// variables  shown in the `pathconf(2)` man page.  Usually, it's the same as
/// the C variable name without the leading `_PC_`.
///
/// POSIX 1003.1-2008 standardizes all of these variables, but some OSes choose
/// not to implement variables that cannot change at runtime.
///
/// # References
///
/// - [pathconf(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/pathconf.html)
/// - [limits.h](https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/limits.h.html)
/// - [unistd.h](https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/unistd.h.html)
#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
#[repr(i32)]
#[non_exhaustive]
pub enum PathconfVar {
    #[cfg(any(
        freebsdlike,
        netbsdlike,
        target_os = "linux",
        target_os = "redox"
    ))]
    /// Minimum number of bits needed to represent, as a signed integer value,
    /// the maximum size of a regular file allowed in the specified directory.
    FILESIZEBITS = libc::_PC_FILESIZEBITS,
    /// Maximum number of links to a single file.
    LINK_MAX = libc::_PC_LINK_MAX,
    /// Maximum number of bytes in a terminal canonical input line.
    MAX_CANON = libc::_PC_MAX_CANON,
    /// Minimum number of bytes for which space is available in a terminal input
    /// queue; therefore, the maximum number of bytes a conforming application
    /// may require to be typed as input before reading them.
    MAX_INPUT = libc::_PC_MAX_INPUT,
    #[cfg(any(
        apple_targets,
        solarish,
        freebsdlike,
        target_os = "netbsd",
    ))]
    /// If a file system supports the reporting of holes (see lseek(2)),
    /// pathconf() and fpathconf() return a positive number that represents the
    /// minimum hole size returned in bytes.  The offsets of holes returned will
    /// be aligned to this same value.  A special value of 1 is returned if the
    /// file system does not specify the minimum hole size but still reports
    /// holes.
    MIN_HOLE_SIZE = libc::_PC_MIN_HOLE_SIZE,
    /// Maximum number of bytes in a filename (not including the terminating
    /// null of a filename string).
    NAME_MAX = libc::_PC_NAME_MAX,
    /// Maximum number of bytes the implementation will store as a pathname in a
    /// user-supplied buffer of unspecified size, including the terminating null
    /// character. Minimum number the implementation will accept as the maximum
    /// number of bytes in a pathname.
    PATH_MAX = libc::_PC_PATH_MAX,
    /// Maximum number of bytes that is guaranteed to be atomic when writing to
    /// a pipe.
    PIPE_BUF = libc::_PC_PIPE_BUF,
    #[cfg(any(
        linux_android,
        solarish,
        netbsdlike,
        target_os = "dragonfly",
        target_os = "redox",
    ))]
    /// Symbolic links can be created.
    POSIX2_SYMLINKS = libc::_PC_2_SYMLINKS,
    #[cfg(any(
        linux_android,
        freebsdlike,
        target_os = "openbsd",
        target_os = "redox"
    ))]
    /// Minimum number of bytes of storage actually allocated for any portion of
    /// a file.
    POSIX_ALLOC_SIZE_MIN = libc::_PC_ALLOC_SIZE_MIN,
    #[cfg(any(
        freebsdlike,
        linux_android,
        target_os = "openbsd"
    ))]
    /// Recommended increment for file transfer sizes between the
    /// `POSIX_REC_MIN_XFER_SIZE` and `POSIX_REC_MAX_XFER_SIZE` values.
    POSIX_REC_INCR_XFER_SIZE = libc::_PC_REC_INCR_XFER_SIZE,
    #[cfg(any(
        linux_android,
        freebsdlike,
        target_os = "openbsd",
        target_os = "redox"
    ))]
    /// Maximum recommended file transfer size.
    POSIX_REC_MAX_XFER_SIZE = libc::_PC_REC_MAX_XFER_SIZE,
    #[cfg(any(
        linux_android,
        freebsdlike,
        target_os = "openbsd",
        target_os = "redox"
    ))]
    /// Minimum recommended file transfer size.
    POSIX_REC_MIN_XFER_SIZE = libc::_PC_REC_MIN_XFER_SIZE,
    #[cfg(any(
        linux_android,
        freebsdlike,
        target_os = "openbsd",
        target_os = "redox"
    ))]
    ///  Recommended file transfer buffer alignment.
    POSIX_REC_XFER_ALIGN = libc::_PC_REC_XFER_ALIGN,
    #[cfg(any(
        linux_android,
        freebsdlike,
        solarish,
        netbsdlike,
        target_os = "redox",
    ))]
    /// Maximum number of bytes in a symbolic link.
    SYMLINK_MAX = libc::_PC_SYMLINK_MAX,
    /// The use of `chown` and `fchown` is restricted to a process with
    /// appropriate privileges, and to changing the group ID of a file only to
    /// the effective group ID of the process or to one of its supplementary
    /// group IDs.
    _POSIX_CHOWN_RESTRICTED = libc::_PC_CHOWN_RESTRICTED,
    /// Pathname components longer than {NAME_MAX} generate an error.
    _POSIX_NO_TRUNC = libc::_PC_NO_TRUNC,
    /// This symbol shall be defined to be the value of a character that shall
    /// disable terminal special character handling.
    _POSIX_VDISABLE = libc::_PC_VDISABLE,
    #[cfg(any(
        linux_android,
        freebsdlike,
        solarish,
        target_os = "openbsd",
        target_os = "redox",
    ))]
    /// Asynchronous input or output operations may be performed for the
    /// associated file.
    _POSIX_ASYNC_IO = libc::_PC_ASYNC_IO,
    #[cfg(any(
        linux_android,
        freebsdlike,
        solarish,
        target_os = "openbsd",
        target_os = "redox",
    ))]
    /// Prioritized input or output operations may be performed for the
    /// associated file.
    _POSIX_PRIO_IO = libc::_PC_PRIO_IO,
    #[cfg(any(
        linux_android,
        freebsdlike,
        solarish,
        netbsdlike,
        target_os = "redox",
    ))]
    /// Synchronized input or output operations may be performed for the
    /// associated file.
    _POSIX_SYNC_IO = libc::_PC_SYNC_IO,
    #[cfg(any(target_os = "dragonfly", target_os = "openbsd"))]
    /// The resolution in nanoseconds for all file timestamps.
    _POSIX_TIMESTAMP_RESOLUTION = libc::_PC_TIMESTAMP_RESOLUTION,
}

/// Like `pathconf`, but works with file descriptors instead of paths (see
/// [fpathconf(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/pathconf.html))
///
/// # Parameters
///
/// - `fd`:   The file descriptor whose variable should be interrogated
/// - `var`:  The pathconf variable to lookup
///
/// # Returns
///
/// - `Ok(Some(x))`: the variable's limit (for limit variables) or its
///     implementation level (for option variables).  Implementation levels are
///     usually a decimal-coded date, such as 200112 for POSIX 2001.12
/// - `Ok(None)`: the variable has no limit (for limit variables) or is
///     unsupported (for option variables)
/// - `Err(x)`: an error occurred
pub fn fpathconf<F: AsFd>(fd: F, var: PathconfVar) -> Result<Option<c_long>> {
    let raw = unsafe {
        Errno::clear();
        libc::fpathconf(fd.as_fd().as_raw_fd(), var as c_int)
    };
    if raw == -1 {
        if Errno::last_raw() == 0 {
            Ok(None)
        } else {
            Err(Errno::last())
        }
    } else {
        Ok(Some(raw))
    }
}

/// Get path-dependent configurable system variables (see
/// [pathconf(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/pathconf.html))
///
/// Returns the value of a path-dependent configurable system variable.  Most
/// supported variables also have associated compile-time constants, but POSIX
/// allows their values to change at runtime.  There are generally two types of
/// `pathconf` variables: options and limits.  See [pathconf(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/pathconf.html) for more details.
///
/// # Parameters
///
/// - `path`: Lookup the value of `var` for this file or directory
/// - `var`:  The `pathconf` variable to lookup
///
/// # Returns
///
/// - `Ok(Some(x))`: the variable's limit (for limit variables) or its
///     implementation level (for option variables).  Implementation levels are
///     usually a decimal-coded date, such as 200112 for POSIX 2001.12
/// - `Ok(None)`: the variable has no limit (for limit variables) or is
///     unsupported (for option variables)
/// - `Err(x)`: an error occurred
pub fn pathconf<P: ?Sized + NixPath>(
    path: &P,
    var: PathconfVar,
) -> Result<Option<c_long>> {
    let raw = path.with_nix_path(|cstr| unsafe {
        Errno::clear();
        libc::pathconf(cstr.as_ptr(), var as c_int)
    })?;
    if raw == -1 {
        if Errno::last_raw() == 0 {
            Ok(None)
        } else {
            Err(Errno::last())
        }
    } else {
        Ok(Some(raw))
    }
}
}

feature! {
#![feature = "feature"]

/// Variable names for `sysconf`
///
/// Nix uses the same naming convention for these variables as the
/// [getconf(1)](https://pubs.opengroup.org/onlinepubs/9699919799/utilities/getconf.html) utility.
/// That is, `SysconfVar` variables have the same name as the abstract variables
/// shown in the `sysconf(3)` man page.  Usually, it's the same as the C
/// variable name without the leading `_SC_`.
///
/// All of these symbols are standardized by POSIX 1003.1-2008, but haven't been
/// implemented by all platforms.
///
/// # References
///
/// - [sysconf(3)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/sysconf.html)
/// - [unistd.h](https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/unistd.h.html)
/// - [limits.h](https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/limits.h.html)
#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
#[repr(i32)]
#[non_exhaustive]
pub enum SysconfVar {
    /// Maximum number of I/O operations in a single list I/O call supported by
    /// the implementation.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    AIO_LISTIO_MAX = libc::_SC_AIO_LISTIO_MAX,
    /// Maximum number of outstanding asynchronous I/O operations supported by
    /// the implementation.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    AIO_MAX = libc::_SC_AIO_MAX,
    #[cfg(any(
        linux_android,
        freebsdlike,
        apple_targets,
        target_os = "openbsd"
    ))]
    /// The maximum amount by which a process can decrease its asynchronous I/O
    /// priority level from its own scheduling priority.
    AIO_PRIO_DELTA_MAX = libc::_SC_AIO_PRIO_DELTA_MAX,
    /// Maximum length of argument to the exec functions including environment data.
    ARG_MAX = libc::_SC_ARG_MAX,
    /// Maximum number of functions that may be registered with `atexit`.
    #[cfg(not(target_os = "redox"))]
    ATEXIT_MAX = libc::_SC_ATEXIT_MAX,
    /// Maximum obase values allowed by the bc utility.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    BC_BASE_MAX = libc::_SC_BC_BASE_MAX,
    /// Maximum number of elements permitted in an array by the bc utility.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    BC_DIM_MAX = libc::_SC_BC_DIM_MAX,
    /// Maximum scale value allowed by the bc utility.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    BC_SCALE_MAX = libc::_SC_BC_SCALE_MAX,
    /// Maximum length of a string constant accepted by the bc utility.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    BC_STRING_MAX = libc::_SC_BC_STRING_MAX,
    /// Maximum number of simultaneous processes per real user ID.
    CHILD_MAX = libc::_SC_CHILD_MAX,
    /// The frequency of the statistics clock in ticks per second.
    CLK_TCK = libc::_SC_CLK_TCK,
    /// Maximum number of weights that can be assigned to an entry of the
    /// LC_COLLATE order keyword in the locale definition file
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    COLL_WEIGHTS_MAX = libc::_SC_COLL_WEIGHTS_MAX,
    /// Maximum number of timer expiration overruns.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    DELAYTIMER_MAX = libc::_SC_DELAYTIMER_MAX,
    /// Maximum number of expressions that can be nested within parentheses by
    /// the expr utility.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    EXPR_NEST_MAX = libc::_SC_EXPR_NEST_MAX,
    #[cfg(any(bsd, solarish, target_os = "linux"))]
    /// Maximum length of a host name (not including the terminating null) as
    /// returned from the `gethostname` function
    HOST_NAME_MAX = libc::_SC_HOST_NAME_MAX,
    /// Maximum number of iovec structures that one process has available for
    /// use with `readv` or `writev`.
    #[cfg(not(target_os = "redox"))]
    IOV_MAX = libc::_SC_IOV_MAX,
    /// Unless otherwise noted, the maximum length, in bytes, of a utility's
    /// input line (either standard input or another file), when the utility is
    /// described as processing text files. The length includes room for the
    /// trailing newline.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    LINE_MAX = libc::_SC_LINE_MAX,
    /// Maximum length of a login name.
    #[cfg(not(target_os = "haiku"))]
    LOGIN_NAME_MAX = libc::_SC_LOGIN_NAME_MAX,
    /// Maximum number of simultaneous supplementary group IDs per process.
    NGROUPS_MAX = libc::_SC_NGROUPS_MAX,
    /// Initial size of `getgrgid_r` and `getgrnam_r` data buffers
    #[cfg(not(target_os = "redox"))]
    GETGR_R_SIZE_MAX = libc::_SC_GETGR_R_SIZE_MAX,
    /// Initial size of `getpwuid_r` and `getpwnam_r` data buffers
    #[cfg(not(target_os = "redox"))]
    GETPW_R_SIZE_MAX = libc::_SC_GETPW_R_SIZE_MAX,
    /// The maximum number of open message queue descriptors a process may hold.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    MQ_OPEN_MAX = libc::_SC_MQ_OPEN_MAX,
    /// The maximum number of message priorities supported by the implementation.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    MQ_PRIO_MAX = libc::_SC_MQ_PRIO_MAX,
    /// A value one greater than the maximum value that the system may assign to
    /// a newly-created file descriptor.
    OPEN_MAX = libc::_SC_OPEN_MAX,
    #[cfg(any(
        freebsdlike,
        apple_targets,
        target_os = "linux",
        target_os = "openbsd"
    ))]
    /// The implementation supports the Advisory Information option.
    _POSIX_ADVISORY_INFO = libc::_SC_ADVISORY_INFO,
    #[cfg(any(bsd, solarish, target_os = "linux"))]
    /// The implementation supports barriers.
    _POSIX_BARRIERS = libc::_SC_BARRIERS,
    /// The implementation supports asynchronous input and output.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    _POSIX_ASYNCHRONOUS_IO = libc::_SC_ASYNCHRONOUS_IO,
    #[cfg(any(bsd, solarish, target_os = "linux"))]
    /// The implementation supports clock selection.
    _POSIX_CLOCK_SELECTION = libc::_SC_CLOCK_SELECTION,
    #[cfg(any(bsd, solarish, target_os = "linux"))]
    /// The implementation supports the Process CPU-Time Clocks option.
    _POSIX_CPUTIME = libc::_SC_CPUTIME,
    /// The implementation supports the File Synchronization option.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    _POSIX_FSYNC = libc::_SC_FSYNC,
    #[cfg(any(
        freebsdlike,
        apple_targets,
        solarish,
        target_os = "linux",
        target_os = "openbsd",
    ))]
    /// The implementation supports the IPv6 option.
    _POSIX_IPV6 = libc::_SC_IPV6,
    /// The implementation supports job control.
    #[cfg(not(target_os = "redox"))]
    _POSIX_JOB_CONTROL = libc::_SC_JOB_CONTROL,
    /// The implementation supports memory mapped Files.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    _POSIX_MAPPED_FILES = libc::_SC_MAPPED_FILES,
    /// The implementation supports the Process Memory Locking option.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    _POSIX_MEMLOCK = libc::_SC_MEMLOCK,
    /// The implementation supports the Range Memory Locking option.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    _POSIX_MEMLOCK_RANGE = libc::_SC_MEMLOCK_RANGE,
    /// The implementation supports memory protection.
    #[cfg(not(target_os = "redox"))]
    _POSIX_MEMORY_PROTECTION = libc::_SC_MEMORY_PROTECTION,
    /// The implementation supports the Message Passing option.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    _POSIX_MESSAGE_PASSING = libc::_SC_MESSAGE_PASSING,
    /// The implementation supports the Monotonic Clock option.
    #[cfg(not(target_os = "redox"))]
    _POSIX_MONOTONIC_CLOCK = libc::_SC_MONOTONIC_CLOCK,
    #[cfg(any(
        linux_android,
        freebsdlike,
        solarish,
        apple_targets,
        target_os = "openbsd",
    ))]
    /// The implementation supports the Prioritized Input and Output option.
    _POSIX_PRIORITIZED_IO = libc::_SC_PRIORITIZED_IO,
    /// The implementation supports the Process Scheduling option.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    _POSIX_PRIORITY_SCHEDULING = libc::_SC_PRIORITY_SCHEDULING,
    #[cfg(any(
        freebsdlike,
        solarish,
        apple_targets,
        target_os = "linux",
        target_os = "openbsd",
    ))]
    /// The implementation supports the Raw Sockets option.
    _POSIX_RAW_SOCKETS = libc::_SC_RAW_SOCKETS,
    #[cfg(any(
        bsd,
        solarish,
        target_os = "linux",
    ))]
    /// The implementation supports read-write locks.
    _POSIX_READER_WRITER_LOCKS = libc::_SC_READER_WRITER_LOCKS,
    #[cfg(any(
        linux_android,
        freebsdlike,
        apple_targets,
        target_os = "openbsd"
    ))]
    /// The implementation supports realtime signals.
    _POSIX_REALTIME_SIGNALS = libc::_SC_REALTIME_SIGNALS,
    #[cfg(any(
        bsd,
        solarish,
        target_os = "linux",
    ))]
    /// The implementation supports the Regular Expression Handling option.
    _POSIX_REGEXP = libc::_SC_REGEXP,
    /// Each process has a saved set-user-ID and a saved set-group-ID.
    #[cfg(not(target_os = "redox"))]
    _POSIX_SAVED_IDS = libc::_SC_SAVED_IDS,
    /// The implementation supports semaphores.
    #[cfg(not(target_os = "redox"))]
    _POSIX_SEMAPHORES = libc::_SC_SEMAPHORES,
    /// The implementation supports the Shared Memory Objects option.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    _POSIX_SHARED_MEMORY_OBJECTS = libc::_SC_SHARED_MEMORY_OBJECTS,
    #[cfg(any(bsd, target_os = "linux",))]
    /// The implementation supports the POSIX shell.
    _POSIX_SHELL = libc::_SC_SHELL,
    #[cfg(any(bsd, target_os = "linux",))]
    /// The implementation supports the Spawn option.
    _POSIX_SPAWN = libc::_SC_SPAWN,
    #[cfg(any(bsd, target_os = "linux",))]
    /// The implementation supports spin locks.
    _POSIX_SPIN_LOCKS = libc::_SC_SPIN_LOCKS,
    #[cfg(any(
        freebsdlike,
        apple_targets,
        target_os = "linux",
        target_os = "openbsd"
    ))]
    /// The implementation supports the Process Sporadic Server option.
    _POSIX_SPORADIC_SERVER = libc::_SC_SPORADIC_SERVER,
    /// The number of replenishment operations that can be simultaneously pending for a particular
    /// sporadic server scheduler.
    #[cfg(any(
        apple_targets,
        target_os = "linux",
        target_os = "openbsd"
    ))]
    _POSIX_SS_REPL_MAX = libc::_SC_SS_REPL_MAX,
    /// The implementation supports the Synchronized Input and Output option.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    _POSIX_SYNCHRONIZED_IO = libc::_SC_SYNCHRONIZED_IO,
    /// The implementation supports the Thread Stack Address Attribute option.
    #[cfg(not(target_os = "redox"))]
    _POSIX_THREAD_ATTR_STACKADDR = libc::_SC_THREAD_ATTR_STACKADDR,
    /// The implementation supports the Thread Stack Size Attribute option.
    #[cfg(not(target_os = "redox"))]
    _POSIX_THREAD_ATTR_STACKSIZE = libc::_SC_THREAD_ATTR_STACKSIZE,
    #[cfg(any(
        apple_targets,
        target_os = "linux",
        netbsdlike,
    ))]
    /// The implementation supports the Thread CPU-Time Clocks option.
    _POSIX_THREAD_CPUTIME = libc::_SC_THREAD_CPUTIME,
    /// The implementation supports the Non-Robust Mutex Priority Inheritance
    /// option.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    _POSIX_THREAD_PRIO_INHERIT = libc::_SC_THREAD_PRIO_INHERIT,
    /// The implementation supports the Non-Robust Mutex Priority Protection option.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    _POSIX_THREAD_PRIO_PROTECT = libc::_SC_THREAD_PRIO_PROTECT,
    /// The implementation supports the Thread Execution Scheduling option.
    #[cfg(not(target_os = "redox"))]
    _POSIX_THREAD_PRIORITY_SCHEDULING = libc::_SC_THREAD_PRIORITY_SCHEDULING,
    #[cfg(any(bsd, target_os = "linux"))]
    /// The implementation supports the Thread Process-Shared Synchronization
    /// option.
    _POSIX_THREAD_PROCESS_SHARED = libc::_SC_THREAD_PROCESS_SHARED,
    #[cfg(any(
        target_os = "dragonfly",
        target_os = "linux",
        target_os = "openbsd"
    ))]
    /// The implementation supports the Robust Mutex Priority Inheritance option.
    _POSIX_THREAD_ROBUST_PRIO_INHERIT = libc::_SC_THREAD_ROBUST_PRIO_INHERIT,
    #[cfg(any(
        target_os = "dragonfly",
        target_os = "linux",
        target_os = "openbsd"
    ))]
    /// The implementation supports the Robust Mutex Priority Protection option.
    _POSIX_THREAD_ROBUST_PRIO_PROTECT = libc::_SC_THREAD_ROBUST_PRIO_PROTECT,
    /// The implementation supports thread-safe functions.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    _POSIX_THREAD_SAFE_FUNCTIONS = libc::_SC_THREAD_SAFE_FUNCTIONS,
    #[cfg(any(
        freebsdlike,
        apple_targets,
        target_os = "linux",
        target_os = "openbsd"
    ))]
    /// The implementation supports the Thread Sporadic Server option.
    _POSIX_THREAD_SPORADIC_SERVER = libc::_SC_THREAD_SPORADIC_SERVER,
    /// The implementation supports threads.
    #[cfg(not(target_os = "redox"))]
    _POSIX_THREADS = libc::_SC_THREADS,
    #[cfg(any(
        freebsdlike,
        apple_targets,
        target_os = "linux",
        target_os = "openbsd"
    ))]
    /// The implementation supports timeouts.
    _POSIX_TIMEOUTS = libc::_SC_TIMEOUTS,
    /// The implementation supports timers.
    #[cfg(not(target_os = "redox"))]
    _POSIX_TIMERS = libc::_SC_TIMERS,
    #[cfg(any(
        freebsdlike,
        apple_targets,
        target_os = "linux",
        target_os = "openbsd"
    ))]
    /// The implementation supports the Trace option.
    _POSIX_TRACE = libc::_SC_TRACE,
    #[cfg(any(
        freebsdlike,
        apple_targets,
        target_os = "linux",
        target_os = "openbsd"
    ))]
    /// The implementation supports the Trace Event Filter option.
    _POSIX_TRACE_EVENT_FILTER = libc::_SC_TRACE_EVENT_FILTER,
    /// Maximum size of a trace event name in characters.
    #[cfg(any(
        apple_targets,
        target_os = "linux",
        target_os = "openbsd"
    ))]
    _POSIX_TRACE_EVENT_NAME_MAX = libc::_SC_TRACE_EVENT_NAME_MAX,
    #[cfg(any(
        freebsdlike,
        apple_targets,
        target_os = "linux",
        target_os = "openbsd"
    ))]
    /// The implementation supports the Trace Inherit option.
    _POSIX_TRACE_INHERIT = libc::_SC_TRACE_INHERIT,
    #[cfg(any(
        freebsdlike,
        apple_targets,
        target_os = "linux",
        target_os = "openbsd"
    ))]
    /// The implementation supports the Trace Log option.
    _POSIX_TRACE_LOG = libc::_SC_TRACE_LOG,
    /// The length in bytes of a trace generation version string or a trace stream name.
    #[cfg(any(
        apple_targets,
        target_os = "linux",
        target_os = "openbsd"
    ))]
    _POSIX_TRACE_NAME_MAX = libc::_SC_TRACE_NAME_MAX,
    /// Maximum number of times `posix_trace_create` may be called from the same or different
    /// processes.
    #[cfg(any(
        apple_targets,
        target_os = "linux",
        target_os = "openbsd"
    ))]
    _POSIX_TRACE_SYS_MAX = libc::_SC_TRACE_SYS_MAX,
    /// Maximum number of user trace event type identifiers for a single process.
    #[cfg(any(
        apple_targets,
        target_os = "linux",
        target_os = "openbsd"
    ))]
    _POSIX_TRACE_USER_EVENT_MAX = libc::_SC_TRACE_USER_EVENT_MAX,
    #[cfg(any(
        freebsdlike,
        apple_targets,
        target_os = "linux",
        target_os = "openbsd"
    ))]
    /// The implementation supports the Typed Memory Objects option.
    _POSIX_TYPED_MEMORY_OBJECTS = libc::_SC_TYPED_MEMORY_OBJECTS,
    /// Integer value indicating version of this standard (C-language binding)
    /// to which the implementation conforms. For implementations conforming to
    /// POSIX.1-2008, the value shall be 200809L.
    _POSIX_VERSION = libc::_SC_VERSION,
    #[cfg(any(bsd, target_os = "linux"))]
    /// The implementation provides a C-language compilation environment with
    /// 32-bit `int`, `long`, `pointer`, and `off_t` types.
    _POSIX_V6_ILP32_OFF32 = libc::_SC_V6_ILP32_OFF32,
    #[cfg(any(bsd, target_os = "linux"))]
    /// The implementation provides a C-language compilation environment with
    /// 32-bit `int`, `long`, and pointer types and an `off_t` type using at
    /// least 64 bits.
    _POSIX_V6_ILP32_OFFBIG = libc::_SC_V6_ILP32_OFFBIG,
    #[cfg(any(bsd, target_os = "linux"))]
    /// The implementation provides a C-language compilation environment with
    /// 32-bit `int` and 64-bit `long`, `pointer`, and `off_t` types.
    _POSIX_V6_LP64_OFF64 = libc::_SC_V6_LP64_OFF64,
    #[cfg(any(bsd, target_os = "linux"))]
    /// The implementation provides a C-language compilation environment with an
    /// `int` type using at least 32 bits and `long`, pointer, and `off_t` types
    /// using at least 64 bits.
    _POSIX_V6_LPBIG_OFFBIG = libc::_SC_V6_LPBIG_OFFBIG,
    /// The implementation supports the C-Language Binding option.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    _POSIX2_C_BIND = libc::_SC_2_C_BIND,
    /// The implementation supports the C-Language Development Utilities option.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    _POSIX2_C_DEV = libc::_SC_2_C_DEV,
    /// The implementation supports the Terminal Characteristics option.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    _POSIX2_CHAR_TERM = libc::_SC_2_CHAR_TERM,
    /// The implementation supports the FORTRAN Development Utilities option.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    _POSIX2_FORT_DEV = libc::_SC_2_FORT_DEV,
    /// The implementation supports the FORTRAN Runtime Utilities option.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    _POSIX2_FORT_RUN = libc::_SC_2_FORT_RUN,
    /// The implementation supports the creation of locales by the localedef
    /// utility.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    _POSIX2_LOCALEDEF = libc::_SC_2_LOCALEDEF,
    #[cfg(any(bsd, target_os = "linux"))]
    /// The implementation supports the Batch Environment Services and Utilities
    /// option.
    _POSIX2_PBS = libc::_SC_2_PBS,
    #[cfg(any(bsd, target_os = "linux"))]
    /// The implementation supports the Batch Accounting option.
    _POSIX2_PBS_ACCOUNTING = libc::_SC_2_PBS_ACCOUNTING,
    #[cfg(any(bsd, target_os = "linux"))]
    /// The implementation supports the Batch Checkpoint/Restart option.
    _POSIX2_PBS_CHECKPOINT = libc::_SC_2_PBS_CHECKPOINT,
    #[cfg(any(bsd, target_os = "linux"))]
    /// The implementation supports the Locate Batch Job Request option.
    _POSIX2_PBS_LOCATE = libc::_SC_2_PBS_LOCATE,
    #[cfg(any(bsd, target_os = "linux"))]
    /// The implementation supports the Batch Job Message Request option.
    _POSIX2_PBS_MESSAGE = libc::_SC_2_PBS_MESSAGE,
    #[cfg(any(bsd, target_os = "linux"))]
    /// The implementation supports the Track Batch Job Request option.
    _POSIX2_PBS_TRACK = libc::_SC_2_PBS_TRACK,
    /// The implementation supports the Software Development Utilities option.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    _POSIX2_SW_DEV = libc::_SC_2_SW_DEV,
    /// The implementation supports the User Portability Utilities option.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    _POSIX2_UPE = libc::_SC_2_UPE,
    /// Integer value indicating version of the Shell and Utilities volume of
    /// POSIX.1 to which the implementation conforms.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    _POSIX2_VERSION = libc::_SC_2_VERSION,
    /// The size of a system page in bytes.
    ///
    /// POSIX also defines an alias named `PAGESIZE`, but Rust does not allow two
    /// enum constants to have the same value, so nix omits `PAGESIZE`.
    PAGE_SIZE = libc::_SC_PAGE_SIZE,
    /// Maximum number of attempts made to destroy a thread's thread-specific data values on thread
    /// exit.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    PTHREAD_DESTRUCTOR_ITERATIONS = libc::_SC_THREAD_DESTRUCTOR_ITERATIONS,
    /// Maximum number of data keys that can be created by a process.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    PTHREAD_KEYS_MAX = libc::_SC_THREAD_KEYS_MAX,
    /// Minimum size in bytes of thread stack storage.
    #[cfg(not(target_os = "redox"))]
    PTHREAD_STACK_MIN = libc::_SC_THREAD_STACK_MIN,
    /// Maximum number of threads that can be created per process.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    PTHREAD_THREADS_MAX = libc::_SC_THREAD_THREADS_MAX,
    /// The maximum number of repeated occurrences of a regular expression permitted when using
    /// interval notation.
    #[cfg(not(target_os = "haiku"))]
    RE_DUP_MAX = libc::_SC_RE_DUP_MAX,
    /// Maximum number of realtime signals reserved for application use.
    #[cfg(any(
        linux_android,
        freebsdlike,
        apple_targets,
        target_os = "openbsd"
    ))]
    RTSIG_MAX = libc::_SC_RTSIG_MAX,
    /// Maximum number of semaphores that a process may have.
    #[cfg(not(target_os = "redox"))]
    SEM_NSEMS_MAX = libc::_SC_SEM_NSEMS_MAX,
    /// The maximum value a semaphore may have.
    #[cfg(any(
        linux_android,
        freebsdlike,
        apple_targets,
        target_os = "openbsd"
    ))]
    SEM_VALUE_MAX = libc::_SC_SEM_VALUE_MAX,
    /// Maximum number of queued signals that a process may send and have pending at the
    /// receiver(s) at any time.
    #[cfg(any(
        linux_android,
        freebsdlike,
        apple_targets,
        target_os = "openbsd"
    ))]
    SIGQUEUE_MAX = libc::_SC_SIGQUEUE_MAX,
    /// The minimum maximum number of streams that a process may have open at any one time.
    STREAM_MAX = libc::_SC_STREAM_MAX,
    /// Maximum number of symbolic links that can be reliably traversed in the resolution of a
    /// pathname in the absence of a loop.
    #[cfg(any(bsd, target_os = "linux"))]
    SYMLOOP_MAX = libc::_SC_SYMLOOP_MAX,
    /// Maximum number of timers per process supported.
    #[cfg(not(target_os = "redox"))]
    TIMER_MAX = libc::_SC_TIMER_MAX,
    /// Maximum length of terminal device name.
    TTY_NAME_MAX = libc::_SC_TTY_NAME_MAX,
    /// The minimum maximum number of types supported for the name of a timezone.
    TZNAME_MAX = libc::_SC_TZNAME_MAX,
    #[cfg(any(
        linux_android,
        freebsdlike,
        apple_targets,
        target_os = "openbsd"
    ))]
    /// The implementation supports the X/Open Encryption Option Group.
    _XOPEN_CRYPT = libc::_SC_XOPEN_CRYPT,
    #[cfg(any(
        linux_android,
        freebsdlike,
        apple_targets,
        target_os = "openbsd"
    ))]
    /// The implementation supports the Issue 4, Version 2 Enhanced
    /// Internationalization Option Group.
    _XOPEN_ENH_I18N = libc::_SC_XOPEN_ENH_I18N,
    #[cfg(any(
        linux_android,
        freebsdlike,
        apple_targets,
        target_os = "openbsd"
    ))]
    /// The implementation supports the XOpen Legacy Option group.
    ///
    /// See Also <https://pubs.opengroup.org/onlinepubs/007904975/basedefs/xbd_chap02.html>
    _XOPEN_LEGACY = libc::_SC_XOPEN_LEGACY,
    #[cfg(any(
        linux_android,
        freebsdlike,
        apple_targets,
        target_os = "openbsd"
    ))]
    /// The implementation supports the X/Open Realtime Option Group.
    _XOPEN_REALTIME = libc::_SC_XOPEN_REALTIME,
    #[cfg(any(
        linux_android,
        freebsdlike,
        apple_targets,
        target_os = "openbsd"
    ))]
    /// The implementation supports the X/Open Realtime Threads Option Group.
    _XOPEN_REALTIME_THREADS = libc::_SC_XOPEN_REALTIME_THREADS,
    /// The implementation supports the Issue 4, Version 2 Shared Memory Option
    /// Group.
    #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
    _XOPEN_SHM = libc::_SC_XOPEN_SHM,
    #[cfg(any(
        freebsdlike,
        apple_targets,
        target_os = "linux",
        target_os = "openbsd"
    ))]
    /// The implementation supports the XSI STREAMS Option Group.
    _XOPEN_STREAMS = libc::_SC_XOPEN_STREAMS,
    #[cfg(any(
        linux_android,
        freebsdlike,
        apple_targets,
        target_os = "openbsd"
    ))]
    /// The implementation supports the XSI option
    _XOPEN_UNIX = libc::_SC_XOPEN_UNIX,
    #[cfg(any(
        linux_android,
        freebsdlike,
        apple_targets,
        target_os = "openbsd"
    ))]
    /// Integer value indicating version of the X/Open Portability Guide to
    /// which the implementation conforms.
    _XOPEN_VERSION = libc::_SC_XOPEN_VERSION,
    /// The number of pages of physical memory. Note that it is possible for
    /// the product of this value to overflow.
    #[cfg(linux_android)]
    _PHYS_PAGES = libc::_SC_PHYS_PAGES,
    /// The number of currently available pages of physical memory.
    #[cfg(linux_android)]
    _AVPHYS_PAGES = libc::_SC_AVPHYS_PAGES,
    /// The number of processors configured.
    #[cfg(linux_android)]
    _NPROCESSORS_CONF = libc::_SC_NPROCESSORS_CONF,
    /// The number of processors currently online (available).
    #[cfg(linux_android)]
    _NPROCESSORS_ONLN = libc::_SC_NPROCESSORS_ONLN,
}

/// Get configurable system variables (see
/// [sysconf(3)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/sysconf.html))
///
/// Returns the value of a configurable system variable.  Most supported
/// variables also have associated compile-time constants, but POSIX
/// allows their values to change at runtime.  There are generally two types of
/// sysconf variables: options and limits.  See sysconf(3) for more details.
///
/// # Returns
///
/// - `Ok(Some(x))`: the variable's limit (for limit variables) or its
///     implementation level (for option variables).  Implementation levels are
///     usually a decimal-coded date, such as 200112 for POSIX 2001.12
/// - `Ok(None)`: the variable has no limit (for limit variables) or is
///     unsupported (for option variables)
/// - `Err(x)`: an error occurred
pub fn sysconf(var: SysconfVar) -> Result<Option<c_long>> {
    let raw = unsafe {
        Errno::clear();
        libc::sysconf(var as c_int)
    };
    if raw == -1 {
        if Errno::last_raw() == 0 {
            Ok(None)
        } else {
            Err(Errno::last())
        }
    } else {
        Ok(Some(raw))
    }
}
}

#[cfg(linux_android)]
#[cfg(feature = "fs")]
mod pivot_root {
    use crate::errno::Errno;
    use crate::{NixPath, Result};

    /// Change the root file system.
    ///
    /// See Also [`pivot_root`](https://man7.org/linux/man-pages/man2/pivot_root.2.html)
    pub fn pivot_root<P1: ?Sized + NixPath, P2: ?Sized + NixPath>(
        new_root: &P1,
        put_old: &P2,
    ) -> Result<()> {
        let res = new_root.with_nix_path(|new_root| {
            put_old.with_nix_path(|put_old| unsafe {
                libc::syscall(
                    libc::SYS_pivot_root,
                    new_root.as_ptr(),
                    put_old.as_ptr(),
                )
            })
        })??;

        Errno::result(res).map(drop)
    }
}

#[cfg(any(linux_android, freebsdlike, target_os = "openbsd"))]
mod setres {
    feature! {
    #![feature = "user"]

    use super::{Gid, Uid};
    use crate::errno::Errno;
    use crate::Result;

    /// Sets the real, effective, and saved uid.
    /// ([see setresuid(2)](https://man7.org/linux/man-pages/man2/setresuid.2.html))
    ///
    /// * `ruid`: real user id
    /// * `euid`: effective user id
    /// * `suid`: saved user id
    /// * returns: Ok or libc error code.
    ///
    /// Err is returned if the user doesn't have permission to set this UID.
    #[inline]
    pub fn setresuid(ruid: Uid, euid: Uid, suid: Uid) -> Result<()> {
        let res =
            unsafe { libc::setresuid(ruid.into(), euid.into(), suid.into()) };

        Errno::result(res).map(drop)
    }

    /// Sets the real, effective, and saved gid.
    /// ([see setresuid(2)](https://man7.org/linux/man-pages/man2/setresuid.2.html))
    ///
    /// * `rgid`: real group id
    /// * `egid`: effective group id
    /// * `sgid`: saved group id
    /// * returns: Ok or libc error code.
    ///
    /// Err is returned if the user doesn't have permission to set this GID.
    #[inline]
    pub fn setresgid(rgid: Gid, egid: Gid, sgid: Gid) -> Result<()> {
        let res =
            unsafe { libc::setresgid(rgid.into(), egid.into(), sgid.into()) };

        Errno::result(res).map(drop)
    }
    }
}

#[cfg(any(linux_android, freebsdlike, target_os = "openbsd"))]
mod getres {
    feature! {
    #![feature = "user"]

    use super::{Gid, Uid};
    use crate::errno::Errno;
    use crate::Result;

    /// Real, effective and saved user IDs.
    #[derive(Debug, Copy, Clone, Eq, PartialEq)]
    pub struct ResUid {
        /// Real UID
        pub real: Uid,
        /// Effective UID
        pub effective: Uid,
        /// Saved UID
        pub saved: Uid,
    }

    /// Real, effective and saved group IDs.
    #[derive(Debug, Copy, Clone, Eq, PartialEq)]
    pub struct ResGid {
        /// Real GID
        pub real: Gid,
        /// Effective GID
        pub effective: Gid,
        /// Saved GID
        pub saved: Gid,
    }

    /// Gets the real, effective, and saved user IDs.
    ///
    /// ([see getresuid(2)](http://man7.org/linux/man-pages/man2/getresuid.2.html))
    ///
    /// #Returns
    ///
    /// - `Ok((Uid, Uid, Uid))`: tuple of real, effective and saved uids on success.
    /// - `Err(x)`: libc error code on failure.
    ///
    #[inline]
    pub fn getresuid() -> Result<ResUid> {
        let mut ruid = libc::uid_t::MAX;
        let mut euid = libc::uid_t::MAX;
        let mut suid = libc::uid_t::MAX;
        let res = unsafe { libc::getresuid(&mut ruid, &mut euid, &mut suid) };

        Errno::result(res).map(|_| ResUid {
            real: Uid(ruid),
            effective: Uid(euid),
            saved: Uid(suid),
        })
    }

    /// Gets the real, effective, and saved group IDs.
    ///
    /// ([see getresgid(2)](http://man7.org/linux/man-pages/man2/getresgid.2.html))
    ///
    /// #Returns
    ///
    /// - `Ok((Gid, Gid, Gid))`: tuple of real, effective and saved gids on success.
    /// - `Err(x)`: libc error code on failure.
    ///
    #[inline]
    pub fn getresgid() -> Result<ResGid> {
        let mut rgid = libc::gid_t::MAX;
        let mut egid = libc::gid_t::MAX;
        let mut sgid = libc::gid_t::MAX;
        let res = unsafe { libc::getresgid(&mut rgid, &mut egid, &mut sgid) };

        Errno::result(res).map(|_| ResGid {
            real: Gid(rgid),
            effective: Gid(egid),
            saved: Gid(sgid),
        })
    }
    }
}

#[cfg(feature = "process")]
#[cfg(target_os = "freebsd")]
libc_bitflags! {
    /// Flags for [`rfork`]
    ///
    /// subset of flags supported by FreeBSD 12.x and onwards
    /// with a safe outcome, thus as `RFMEM` can possibly lead to undefined behavior,
    /// it is not in the list. And `rfork_thread` is deprecated.
    pub struct RforkFlags: libc::c_int {
        /// creates a new process.
        RFPROC;
        /// the child process will detach from the parent.
        /// however, no status will be emitted at child's exit.
        RFNOWAIT;
        /// the file descriptor's table will be copied
        RFFDG;
        /// a new file descriptor's table will be created
        RFCFDG;
        /// force sharing the sigacts structure between
        /// the child and the parent.
        RFSIGSHARE;
        /// enables kernel thread support.
        RFTHREAD;
        /// sets a status to emit at child's exit.
        RFTSIGZMB;
        /// linux's behavior compatibility setting.
        /// emits SIGUSR1 as opposed to SIGCHLD upon child's exit.
        RFLINUXTHPN;
    }
}

feature! {
#![feature = "process"]
#[cfg(target_os = "freebsd")]
/// Like [`fork`], `rfork` can be used to have a tigher control about which
/// resources child and parent process will be sharing, file descriptors,
/// address spaces and child exit's behavior.
///
/// # Safety
///
/// The same restrictions apply as for [`fork`].
///
/// # See Also
///
/// * [rfork(2)](https://man.freebsd.org/cgi/man.cgi?query=rfork)
pub unsafe fn rfork(flags: RforkFlags) -> Result<ForkResult> {
    use ForkResult::*;
    let res = unsafe { libc::rfork(flags.bits()) };

    Errno::result(res).map(|res| match res {
        0 => Child,
        res => Parent { child: Pid(res) },
    })
}
}

#[cfg(feature = "fs")]
libc_bitflags! {
    /// Options for access()
    #[cfg_attr(docsrs, doc(cfg(feature = "fs")))]
    pub struct AccessFlags : c_int {
        /// Test for existence of file.
        F_OK;
        /// Test for read permission.
        R_OK;
        /// Test for write permission.
        W_OK;
        /// Test for execute (search) permission.
        X_OK;
    }
}

feature! {
#![feature = "fs"]

/// Checks the file named by `path` for accessibility according to the flags given by `amode`
/// See [access(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/access.html)
pub fn access<P: ?Sized + NixPath>(path: &P, amode: AccessFlags) -> Result<()> {
    let res = path.with_nix_path(|cstr| unsafe {
        libc::access(cstr.as_ptr(), amode.bits())
    })?;
    Errno::result(res).map(drop)
}

/// Checks the file named by `path` for accessibility according to the flags given by `mode`
///
/// If `dirfd` has a value, then `path` is relative to directory associated with the file descriptor.
///
/// If `dirfd` is `None`, then `path` is relative to the current working directory.
///
/// # References
///
/// [faccessat(2)](http://pubs.opengroup.org/onlinepubs/9699919799/functions/faccessat.html)
// redox: does not appear to support the *at family of syscalls.
#[cfg(not(target_os = "redox"))]
pub fn faccessat<P: ?Sized + NixPath>(
    dirfd: Option<RawFd>,
    path: &P,
    mode: AccessFlags,
    flags: AtFlags,
) -> Result<()> {
    let res = path.with_nix_path(|cstr| unsafe {
        libc::faccessat(
            at_rawfd(dirfd),
            cstr.as_ptr(),
            mode.bits(),
            flags.bits(),
        )
    })?;
    Errno::result(res).map(drop)
}

/// Checks the file named by `path` for accessibility according to the flags given
/// by `mode` using effective UID, effective GID and supplementary group lists.
///
/// # References
///
/// * [FreeBSD man page](https://www.freebsd.org/cgi/man.cgi?query=eaccess&sektion=2&n=1)
/// * [Linux man page](https://man7.org/linux/man-pages/man3/euidaccess.3.html)
#[cfg(any(
    freebsdlike,
    all(target_os = "linux", not(target_env = "uclibc")),
))]
pub fn eaccess<P: ?Sized + NixPath>(path: &P, mode: AccessFlags) -> Result<()> {
    let res = path.with_nix_path(|cstr| unsafe {
        libc::eaccess(cstr.as_ptr(), mode.bits())
    })?;
    Errno::result(res).map(drop)
}
}

feature! {
#![feature = "user"]

/// Representation of a User, based on `libc::passwd`
///
/// The reason some fields in this struct are `String` and others are `CString` is because some
/// fields are based on the user's locale, which could be non-UTF8, while other fields are
/// guaranteed to conform to [`NAME_REGEX`](https://serverfault.com/a/73101/407341), which only
/// contains ASCII.
#[cfg(not(target_os = "redox"))] // RedoxFS does not support passwd
#[derive(Debug, Clone, Eq, PartialEq)]
pub struct User {
    /// Username
    pub name: String,
    /// User password (probably hashed)
    pub passwd: CString,
    /// User ID
    pub uid: Uid,
    /// Group ID
    pub gid: Gid,
    /// User information
    #[cfg(not(all(target_os = "android", target_pointer_width = "32")))]
    pub gecos: CString,
    /// Home directory
    pub dir: PathBuf,
    /// Path to shell
    pub shell: PathBuf,
    /// Login class
    #[cfg(not(any(
        linux_android,
        solarish,
        target_os = "aix",
        target_os = "fuchsia",
        target_os = "haiku",
        target_os = "hurd",
    )))]
    pub class: CString,
    /// Last password change
    #[cfg(not(any(
        linux_android,
        solarish,
        target_os = "aix",
        target_os = "fuchsia",
        target_os = "haiku",
        target_os = "hurd",
    )))]
    pub change: libc::time_t,
    /// Expiration time of account
    #[cfg(not(any(
        linux_android,
        solarish,
        target_os = "aix",
        target_os = "fuchsia",
        target_os = "haiku",
        target_os = "hurd",
    )))]
    pub expire: libc::time_t,
}

#[cfg(not(target_os = "redox"))] //RedoxFS does not support passwd
impl From<&libc::passwd> for User {
    fn from(pw: &libc::passwd) -> User {
        unsafe {
            User {
                name: if pw.pw_name.is_null() {
                    Default::default()
                } else {
                    CStr::from_ptr(pw.pw_name).to_string_lossy().into_owned()
                },
                passwd: if pw.pw_passwd.is_null() {
                    Default::default()
                } else {
                    CString::new(CStr::from_ptr(pw.pw_passwd).to_bytes())
                        .unwrap()
                },
                #[cfg(not(all(
                    target_os = "android",
                    target_pointer_width = "32"
                )))]
                gecos: if pw.pw_gecos.is_null() {
                    Default::default()
                } else {
                    CString::new(CStr::from_ptr(pw.pw_gecos).to_bytes())
                        .unwrap()
                },
                dir: if pw.pw_dir.is_null() {
                    Default::default()
                } else {
                    PathBuf::from(OsStr::from_bytes(
                        CStr::from_ptr(pw.pw_dir).to_bytes(),
                    ))
                },
                shell: if pw.pw_shell.is_null() {
                    Default::default()
                } else {
                    PathBuf::from(OsStr::from_bytes(
                        CStr::from_ptr(pw.pw_shell).to_bytes(),
                    ))
                },
                uid: Uid::from_raw(pw.pw_uid),
                gid: Gid::from_raw(pw.pw_gid),
                #[cfg(not(any(
                    linux_android,
                    solarish,
                    target_os = "aix",
                    target_os = "fuchsia",
                    target_os = "haiku",
                    target_os = "hurd",
                )))]
                class: CString::new(CStr::from_ptr(pw.pw_class).to_bytes())
                    .unwrap(),
                #[cfg(not(any(
                    linux_android,
                    solarish,
                    target_os = "aix",
                    target_os = "fuchsia",
                    target_os = "haiku",
                    target_os = "hurd",
                )))]
                change: pw.pw_change,
                #[cfg(not(any(
                    linux_android,
                    solarish,
                    target_os = "aix",
                    target_os = "fuchsia",
                    target_os = "haiku",
                    target_os = "hurd",
                )))]
                expire: pw.pw_expire,
            }
        }
    }
}

#[cfg(not(target_os = "redox"))] // RedoxFS does not support passwd
impl From<User> for libc::passwd {
    fn from(u: User) -> Self {
        let name = match CString::new(u.name) {
            Ok(n) => n.into_raw(),
            Err(_) => CString::new("").unwrap().into_raw(),
        };
        let dir = match u.dir.into_os_string().into_string() {
            Ok(s) => CString::new(s.as_str()).unwrap().into_raw(),
            Err(_) => CString::new("").unwrap().into_raw(),
        };
        let shell = match u.shell.into_os_string().into_string() {
            Ok(s) => CString::new(s.as_str()).unwrap().into_raw(),
            Err(_) => CString::new("").unwrap().into_raw(),
        };
        Self {
            pw_name: name,
            pw_passwd: u.passwd.into_raw(),
            #[cfg(not(all(
                target_os = "android",
                target_pointer_width = "32"
            )))]
            pw_gecos: u.gecos.into_raw(),
            pw_dir: dir,
            pw_shell: shell,
            pw_uid: u.uid.0,
            pw_gid: u.gid.0,
            #[cfg(not(any(
                linux_android,
                solarish,
                target_os = "aix",
                target_os = "fuchsia",
                target_os = "haiku",
                target_os = "hurd",
            )))]
            pw_class: u.class.into_raw(),
            #[cfg(not(any(
                linux_android,
                solarish,
                target_os = "aix",
                target_os = "fuchsia",
                target_os = "haiku",
                target_os = "hurd",
            )))]
            pw_change: u.change,
            #[cfg(not(any(
                linux_android,
                solarish,
                target_os = "aix",
                target_os = "fuchsia",
                target_os = "haiku",
                target_os = "hurd",
            )))]
            pw_expire: u.expire,
            #[cfg(solarish)]
            pw_age: CString::new("").unwrap().into_raw(),
            #[cfg(solarish)]
            pw_comment: CString::new("").unwrap().into_raw(),
            #[cfg(freebsdlike)]
            pw_fields: 0,
        }
    }
}

#[cfg(not(target_os = "redox"))] // RedoxFS does not support passwd
impl User {
    /// # Safety
    ///
    /// If `f` writes to its `*mut *mut libc::passwd` parameter, then it must
    /// also initialize the value pointed to by its `*mut libc::group`
    /// parameter.
    unsafe fn from_anything<F>(f: F) -> Result<Option<Self>>
    where
        F: Fn(
            *mut libc::passwd,
            *mut c_char,
            libc::size_t,
            *mut *mut libc::passwd,
        ) -> libc::c_int,
    {
        let buflimit = 1048576;
        let bufsize = match sysconf(SysconfVar::GETPW_R_SIZE_MAX) {
            Ok(Some(n)) => n as usize,
            Ok(None) | Err(_) => 16384,
        };

        let mut cbuf = Vec::with_capacity(bufsize);
        let mut pwd = mem::MaybeUninit::<libc::passwd>::uninit();
        let mut res = ptr::null_mut();

        loop {
            let error = f(
                pwd.as_mut_ptr(),
                cbuf.as_mut_ptr(),
                cbuf.capacity(),
                &mut res,
            );
            if error == 0 {
                if res.is_null() {
                    return Ok(None);
                } else {
                    // SAFETY: `f` guarantees that `pwd` is initialized if `res`
                    // is not null.
                    let pwd = unsafe { pwd.assume_init() };
                    return Ok(Some(User::from(&pwd)));
                }
            } else if Errno::last() == Errno::ERANGE {
                // Trigger the internal buffer resizing logic.
                reserve_double_buffer_size(&mut cbuf, buflimit)?;
            } else {
                return Err(Errno::last());
            }
        }
    }

    /// Get a user by UID.
    ///
    /// Internally, this function calls
    /// [getpwuid_r(3)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/getpwuid_r.html)
    ///
    /// # Examples
    ///
    /// ```
    /// use nix::unistd::{Uid, User};
    /// // Returns an Result<Option<User>>, thus the double unwrap.
    /// let res = User::from_uid(Uid::from_raw(0)).unwrap().unwrap();
    /// assert_eq!(res.name, "root");
    /// ```
    pub fn from_uid(uid: Uid) -> Result<Option<Self>> {
        // SAFETY: `getpwuid_r` will write to `res` if it initializes the value
        // at `pwd`.
        unsafe {
            User::from_anything(|pwd, cbuf, cap, res| {
                libc::getpwuid_r(uid.0, pwd, cbuf, cap, res)
            })
        }
    }

    /// Get a user by name.
    ///
    /// Internally, this function calls
    /// [getpwnam_r(3)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/getpwnam_r.html)
    ///
    /// # Examples
    ///
    /// ```
    /// use nix::unistd::User;
    /// // Returns an Result<Option<User>>, thus the double unwrap.
    /// let res = User::from_name("root").unwrap().unwrap();
    /// assert_eq!(res.name, "root");
    /// ```
    pub fn from_name(name: &str) -> Result<Option<Self>> {
        let name = match CString::new(name) {
            Ok(c_str) => c_str,
            Err(_nul_error) => return Ok(None),
        };
        // SAFETY: `getpwnam_r` will write to `res` if it initializes the value
        // at `pwd`.
        unsafe {
            User::from_anything(|pwd, cbuf, cap, res| {
                libc::getpwnam_r(name.as_ptr(), pwd, cbuf, cap, res)
            })
        }
    }
}

/// Representation of a Group, based on `libc::group`
#[cfg(not(target_os = "redox"))] // RedoxFS does not support passwd
#[derive(Debug, Clone, Eq, PartialEq)]
pub struct Group {
    /// Group name
    pub name: String,
    /// Group password
    pub passwd: CString,
    /// Group ID
    pub gid: Gid,
    /// List of Group members
    pub mem: Vec<String>,
}

#[cfg(not(target_os = "redox"))] // RedoxFS does not support passwd
impl From<&libc::group> for Group {
    fn from(gr: &libc::group) -> Group {
        unsafe {
            Group {
                name: if gr.gr_name.is_null() {
                    Default::default()
                } else {
                    CStr::from_ptr(gr.gr_name).to_string_lossy().into_owned()
                },
                passwd: if gr.gr_passwd.is_null() {
                    Default::default()
                } else {
                    CString::new(CStr::from_ptr(gr.gr_passwd).to_bytes())
                        .unwrap()
                },
                gid: Gid::from_raw(gr.gr_gid),
                mem: if gr.gr_mem.is_null() {
                    Default::default()
                } else {
                    Group::members(gr.gr_mem)
                },
            }
        }
    }
}

#[cfg(not(target_os = "redox"))] // RedoxFS does not support passwd
impl Group {
    unsafe fn members(mem: *mut *mut c_char) -> Vec<String> {
        let mut ret = Vec::new();

        for i in 0.. {
            let u = unsafe { mem.offset(i).read_unaligned() };
            if u.is_null() {
                break;
            } else {
                let s = unsafe {CStr::from_ptr(u).to_string_lossy().into_owned()};
                ret.push(s);
            }
        }

        ret
    }
    /// # Safety
    ///
    /// If `f` writes to its `*mut *mut libc::group` parameter, then it must
    /// also initialize the value pointed to by its `*mut libc::group`
    /// parameter.
    unsafe fn from_anything<F>(f: F) -> Result<Option<Self>>
    where
        F: Fn(
            *mut libc::group,
            *mut c_char,
            libc::size_t,
            *mut *mut libc::group,
        ) -> libc::c_int,
    {
        let buflimit = 1048576;
        let bufsize = match sysconf(SysconfVar::GETGR_R_SIZE_MAX) {
            Ok(Some(n)) => n as usize,
            Ok(None) | Err(_) => 16384,
        };

        let mut cbuf = Vec::with_capacity(bufsize);
        let mut grp = mem::MaybeUninit::<libc::group>::uninit();
        let mut res = ptr::null_mut();

        loop {
            let error = f(
                grp.as_mut_ptr(),
                cbuf.as_mut_ptr(),
                cbuf.capacity(),
                &mut res,
            );
            if error == 0 {
                if res.is_null() {
                    return Ok(None);
                } else {
                    // SAFETY: `f` guarantees that `grp` is initialized if `res`
                    // is not null.
                    let grp = unsafe { grp.assume_init() };
                    return Ok(Some(Group::from(&grp)));
                }
            } else if Errno::last() == Errno::ERANGE {
                // Trigger the internal buffer resizing logic.
                reserve_double_buffer_size(&mut cbuf, buflimit)?;
            } else {
                return Err(Errno::last());
            }
        }
    }

    /// Get a group by GID.
    ///
    /// Internally, this function calls
    /// [getgrgid_r(3)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/getpwuid_r.html)
    ///
    /// # Examples
    ///
    // Disable this test on all OS except Linux as root group may not exist.
    #[cfg_attr(not(target_os = "linux"), doc = " ```no_run")]
    #[cfg_attr(target_os = "linux", doc = " ```")]
    /// use nix::unistd::{Gid, Group};
    /// // Returns an Result<Option<Group>>, thus the double unwrap.
    /// let res = Group::from_gid(Gid::from_raw(0)).unwrap().unwrap();
    /// assert!(res.name == "root");
    /// ```
    pub fn from_gid(gid: Gid) -> Result<Option<Self>> {
        // SAFETY: `getgrgid_r` will write to `res` if it initializes the value
        // at `grp`.
        unsafe {
            Group::from_anything(|grp, cbuf, cap, res| {
                libc::getgrgid_r(gid.0, grp, cbuf, cap, res)
            })
        }
    }

    /// Get a group by name.
    ///
    /// Internally, this function calls
    /// [getgrnam_r(3)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/getpwuid_r.html)
    ///
    /// # Examples
    ///
    // Disable this test on all OS except Linux as root group may not exist.
    #[cfg_attr(not(target_os = "linux"), doc = " ```no_run")]
    #[cfg_attr(target_os = "linux", doc = " ```")]
    /// use nix::unistd::Group;
    /// // Returns an Result<Option<Group>>, thus the double unwrap.
    /// let res = Group::from_name("root").unwrap().unwrap();
    /// assert!(res.name == "root");
    /// ```
    pub fn from_name(name: &str) -> Result<Option<Self>> {
        let name = match CString::new(name) {
            Ok(c_str) => c_str,
            Err(_nul_error) => return Ok(None),
        };
        // SAFETY: `getgrnam_r` will write to `res` if it initializes the value
        // at `grp`.
        unsafe {
            Group::from_anything(|grp, cbuf, cap, res| {
                libc::getgrnam_r(name.as_ptr(), grp, cbuf, cap, res)
            })
        }
    }
}
}

feature! {
#![feature = "term"]

/// Get the name of the terminal device that is open on file descriptor fd
/// (see [`ttyname(3)`](https://man7.org/linux/man-pages/man3/ttyname.3.html)).
#[cfg(not(target_os = "fuchsia"))]
pub fn ttyname<F: AsFd>(fd: F) -> Result<PathBuf> {
    #[cfg(not(target_os = "hurd"))]
    const PATH_MAX: usize = libc::PATH_MAX as usize;
    #[cfg(target_os = "hurd")]
    const PATH_MAX: usize = 1024; // Hurd does not define a hard limit, so try a guess first
    let mut buf = vec![0_u8; PATH_MAX];
    let c_buf = buf.as_mut_ptr().cast();

    let ret = unsafe { libc::ttyname_r(fd.as_fd().as_raw_fd(), c_buf, buf.len()) };
    if ret != 0 {
        return Err(Errno::from_raw(ret));
    }

    CStr::from_bytes_until_nul(&buf[..])
        .map(|s| OsStr::from_bytes(s.to_bytes()).into())
        .map_err(|_| Errno::EINVAL)
}
}

feature! {
#![all(feature = "socket", feature = "user")]

/// Get the effective user ID and group ID associated with a Unix domain socket.
///
/// See also [getpeereid(3)](https://www.freebsd.org/cgi/man.cgi?query=getpeereid)
#[cfg(bsd)]
pub fn getpeereid<F: AsFd>(fd: F) -> Result<(Uid, Gid)> {
    let mut uid = 1;
    let mut gid = 1;

    let ret = unsafe { libc::getpeereid(fd.as_fd().as_raw_fd(), &mut uid, &mut gid) };

    Errno::result(ret).map(|_| (Uid(uid), Gid(gid)))
}
}

feature! {
#![all(feature = "fs")]

/// Set the file flags.
///
/// See also [chflags(2)](https://www.freebsd.org/cgi/man.cgi?query=chflags&sektion=2)
#[cfg(bsd)]
pub fn chflags<P: ?Sized + NixPath>(path: &P, flags: FileFlag) -> Result<()> {
    let res = path.with_nix_path(|cstr| unsafe {
        libc::chflags(cstr.as_ptr(), flags.bits())
    })?;

    Errno::result(res).map(drop)
}
}