       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

    use crate::os::unix::prelude::*;

    use crate::ffi::{CStr, CString, OsStr, OsString};
    use crate::fmt;
    use crate::io::{self, Error, ErrorKind, IoSlice, IoSliceMut, SeekFrom};
    use crate::mem;
    use crate::path::{Path, PathBuf};
    use crate::ptr;
    use crate::sync::Arc;
    use crate::sys::fd::FileDesc;
    use crate::sys::time::SystemTime;
    use crate::sys::{cvt, cvt_r};
    use crate::sys_common::{AsInner, FromInner};

    use libc::{c_int, mode_t};

    #[cfg(any(target_os = "linux", target_os = "emscripten", target_os = "android"))]
    use libc::dirfd;
    #[cfg(any(target_os = "linux", target_os = "emscripten"))]
    use libc::fstatat64;
    #[cfg(not(any(
        target_os = "linux",
        target_os = "emscripten",
        target_os = "solaris",
        target_os = "illumos",
        target_os = "l4re",
        target_os = "fuchsia",
        target_os = "redox"
    )))]
    use libc::readdir_r as readdir64_r;
    #[cfg(target_os = "android")]
    use libc::{
        dirent as dirent64, fstat as fstat64, fstatat as fstatat64, lseek64, lstat as lstat64,
        open as open64, stat as stat64,
    };
    #[cfg(not(any(
        target_os = "linux",
        target_os = "emscripten",
        target_os = "l4re",
        target_os = "android"
    )))]
    use libc::{
        dirent as dirent64, fstat as fstat64, ftruncate as ftruncate64, lseek as lseek64,
        lstat as lstat64, off_t as off64_t, open as open64, stat as stat64,
    };
    #[cfg(any(target_os = "linux", target_os = "emscripten", target_os = "l4re"))]
    use libc::{
        dirent64, fstat64, ftruncate64, lseek64, lstat64, off64_t, open64, readdir64_r, stat64,
    };

    pub use crate::sys_common::fs::remove_dir_all;

    pub struct File(FileDesc);

    // FIXME: This should be available on Linux with all `target_env`.
    // But currently only glibc exposes `statx` fn and structs.
    // We don't want to import unverified raw C structs here directly.
    // https://github.com/rust-lang/rust/pull/67774
    macro_rules! cfg_has_statx {
        ({ $($then_tt:tt)* } else { $($else_tt:tt)* }) => {
            cfg_if::cfg_if! {
                if #[cfg(all(target_os = "linux", target_env = "gnu"))] {
                    $($then_tt)*
                } else {
                    $($else_tt)*
                }
            }
        };
        ($($block_inner:tt)*) => {
            #[cfg(all(target_os = "linux", target_env = "gnu"))]
            {
                $($block_inner)*
            }
        };
    }

    cfg_has_statx! {{
        #[derive(Clone)]
        pub struct FileAttr {
            stat: stat64,
            statx_extra_fields: Option<StatxExtraFields>,
        }

        #[derive(Clone)]
        struct StatxExtraFields {
            // This is needed to check if btime is supported by the filesystem.
            stx_mask: u32,
            stx_btime: libc::statx_timestamp,
        }

        // We prefer `statx` on Linux if available, which contains file creation time.
        // Default `stat64` contains no creation time.
        unsafe fn try_statx(
            fd: c_int,
            path: *const libc::c_char,
            flags: i32,
            mask: u32,
        ) -> Option<io::Result<FileAttr>> {
            use crate::sync::atomic::{AtomicU8, Ordering};

            // Linux kernel prior to 4.11 or glibc prior to glibc 2.28 don't support `statx`
            // We store the availability in global to avoid unnecessary syscalls.
            // 0: Unknown
            // 1: Not available
            // 2: Available
            static STATX_STATE: AtomicU8 = AtomicU8::new(0);
            syscall! {
                fn statx(
                    fd: c_int,
                    pathname: *const libc::c_char,
                    flags: c_int,
                    mask: libc::c_uint,
                    statxbuf: *mut libc::statx
                ) -> c_int
            }

            match STATX_STATE.load(Ordering::Relaxed) {
                0 => {
                    // It is a trick to call `statx` with NULL pointers to check if the syscall
                    // is available. According to the manual, it is expected to fail with EFAULT.
                    // We do this mainly for performance, since it is nearly hundreds times
                    // faster than a normal successful call.
                    let err = cvt(statx(0, ptr::null(), 0, libc::STATX_ALL, ptr::null_mut()))
                        .err()
                        .and_then(|e| e.raw_os_error());
                    // We don't check `err == Some(libc::ENOSYS)` because the syscall may be limited
                    // and returns `EPERM`. Listing all possible errors seems not a good idea.
                    // See: https://github.com/rust-lang/rust/issues/65662
                    if err != Some(libc::EFAULT) {
                        STATX_STATE.store(1, Ordering::Relaxed);
                        return None;
                    }
                    STATX_STATE.store(2, Ordering::Relaxed);
                }
                1 => return None,
                _ => {}
            }

            let mut buf: libc::statx = mem::zeroed();
            if let Err(err) = cvt(statx(fd, path, flags, mask, &mut buf)) {
                return Some(Err(err));
            }

            // We cannot fill `stat64` exhaustively because of private padding fields.
            let mut stat: stat64 = mem::zeroed();
            // `c_ulong` on gnu-mips, `dev_t` otherwise
            stat.st_dev = libc::makedev(buf.stx_dev_major, buf.stx_dev_minor) as _;
            stat.st_ino = buf.stx_ino as libc::ino64_t;
            stat.st_nlink = buf.stx_nlink as libc::nlink_t;
            stat.st_mode = buf.stx_mode as libc::mode_t;
            stat.st_uid = buf.stx_uid as libc::uid_t;
            stat.st_gid = buf.stx_gid as libc::gid_t;
            stat.st_rdev = libc::makedev(buf.stx_rdev_major, buf.stx_rdev_minor) as _;
            stat.st_size = buf.stx_size as off64_t;
            stat.st_blksize = buf.stx_blksize as libc::blksize_t;
            stat.st_blocks = buf.stx_blocks as libc::blkcnt64_t;
            stat.st_atime = buf.stx_atime.tv_sec as libc::time_t;
            // `i64` on gnu-x86_64-x32, `c_ulong` otherwise.
            stat.st_atime_nsec = buf.stx_atime.tv_nsec as _;
            stat.st_mtime = buf.stx_mtime.tv_sec as libc::time_t;
            stat.st_mtime_nsec = buf.stx_mtime.tv_nsec as _;
            stat.st_ctime = buf.stx_ctime.tv_sec as libc::time_t;
            stat.st_ctime_nsec = buf.stx_ctime.tv_nsec as _;

            let extra = StatxExtraFields {
                stx_mask: buf.stx_mask,
                stx_btime: buf.stx_btime,
            };

            Some(Ok(FileAttr { stat, statx_extra_fields: Some(extra) }))
        }

    } else {
        #[derive(Clone)]
        pub struct FileAttr {
            stat: stat64,
        }
    }}

    // all DirEntry's will have a reference to this struct
    struct InnerReadDir {
        dirp: Dir,
        root: PathBuf,
    }

    #[derive(Clone)]
    pub struct ReadDir {
        inner: Arc<InnerReadDir>,
        end_of_stream: bool,
    }

    struct Dir(*mut libc::DIR);

    unsafe impl Send for Dir {}
    unsafe impl Sync for Dir {}

    pub struct DirEntry {
        entry: dirent64,
        dir: ReadDir,
        // We need to store an owned copy of the entry name
        // on Solaris and Fuchsia because a) it uses a zero-length
        // array to store the name, b) its lifetime between readdir
        // calls is not guaranteed.
        #[cfg(any(
            target_os = "solaris",
            target_os = "illumos",
            target_os = "fuchsia",
            target_os = "redox"
        ))]
        name: Box<[u8]>,
    }

    #[derive(Clone, Debug)]
    pub struct OpenOptions {
        // generic
        read: bool,
        write: bool,
        append: bool,
        truncate: bool,
        create: bool,
        create_new: bool,
        // system-specific
        custom_flags: i32,
        mode: mode_t,
    }

    #[derive(Clone, PartialEq, Eq, Debug)]
    pub struct FilePermissions {
        mode: mode_t,
    }

    #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
    pub struct FileType {
        mode: mode_t,
    }

    #[derive(Debug)]
    pub struct DirBuilder {
        mode: mode_t,
    }

    cfg_has_statx! {{
        impl FileAttr {
            fn from_stat64(stat: stat64) -> Self {
                Self { stat, statx_extra_fields: None }
            }
        }
    } else {
        impl FileAttr {
            fn from_stat64(stat: stat64) -> Self {
                Self { stat }
            }
        }
    }}

    impl FileAttr {
        pub fn size(&self) -> u64 {
            self.stat.st_size as u64
        }
        pub fn perm(&self) -> FilePermissions {
            FilePermissions { mode: (self.stat.st_mode as mode_t) }
        }

        pub fn file_type(&self) -> FileType {
            FileType { mode: self.stat.st_mode as mode_t }
        }
    }

    #[cfg(target_os = "netbsd")]
    impl FileAttr {
        pub fn modified(&self) -> io::Result<SystemTime> {
            Ok(SystemTime::from(libc::timespec {
                tv_sec: self.stat.st_mtime as libc::time_t,
                tv_nsec: self.stat.st_mtimensec as libc::c_long,
            }))
        }

        pub fn accessed(&self) -> io::Result<SystemTime> {
            Ok(SystemTime::from(libc::timespec {
                tv_sec: self.stat.st_atime as libc::time_t,
                tv_nsec: self.stat.st_atimensec as libc::c_long,
            }))
        }

        pub fn created(&self) -> io::Result<SystemTime> {
            Ok(SystemTime::from(libc::timespec {
                tv_sec: self.stat.st_birthtime as libc::time_t,
                tv_nsec: self.stat.st_birthtimensec as libc::c_long,
            }))
        }
    }

    #[cfg(not(target_os = "netbsd"))]
    impl FileAttr {
        pub fn modified(&self) -> io::Result<SystemTime> {
            Ok(SystemTime::from(libc::timespec {
                tv_sec: self.stat.st_mtime as libc::time_t,
                tv_nsec: self.stat.st_mtime_nsec as _,
            }))
        }

        pub fn accessed(&self) -> io::Result<SystemTime> {
            Ok(SystemTime::from(libc::timespec {
                tv_sec: self.stat.st_atime as libc::time_t,
                tv_nsec: self.stat.st_atime_nsec as _,
            }))
        }

        #[cfg(any(
            target_os = "freebsd",
            target_os = "openbsd",
            target_os = "macos",
            target_os = "ios"
        ))]
        pub fn created(&self) -> io::Result<SystemTime> {
            Ok(SystemTime::from(libc::timespec {
                tv_sec: self.stat.st_birthtime as libc::time_t,
                tv_nsec: self.stat.st_birthtime_nsec as libc::c_long,
            }))
        }

        #[cfg(not(any(
            target_os = "freebsd",
            target_os = "openbsd",
            target_os = "macos",
            target_os = "ios"
        )))]
        pub fn created(&self) -> io::Result<SystemTime> {
            cfg_has_statx! {
                if let Some(ext) = &self.statx_extra_fields {
                    return if (ext.stx_mask & libc::STATX_BTIME) != 0 {
                        Ok(SystemTime::from(libc::timespec {
                            tv_sec: ext.stx_btime.tv_sec as libc::time_t,
                            tv_nsec: ext.stx_btime.tv_nsec as _,
                        }))
                    } else {
                        Err(io::Error::new(
                            io::ErrorKind::Other,
                            "creation time is not available for the filesystem",
                        ))
                    };
                }
            }

            Err(io::Error::new(
                io::ErrorKind::Other,
                "creation time is not available on this platform \
                                currently",
            ))
        }
    }

    impl AsInner<stat64> for FileAttr {
        fn as_inner(&self) -> &stat64 {
            &self.stat
        }
    }

    impl FilePermissions {
        pub fn readonly(&self) -> bool {
            // check if any class (owner, group, others) has write permission
            self.mode & 0o222 == 0
        }

        pub fn set_readonly(&mut self, readonly: bool) {
            if readonly {
                // remove write permission for all classes; equivalent to `chmod a-w <file>`
                self.mode &= !0o222;
            } else {
                // add write permission for all classes; equivalent to `chmod a+w <file>`
                self.mode |= 0o222;
            }
        }
        pub fn mode(&self) -> u32 {
            self.mode as u32
        }
    }

    impl FileType {
        pub fn is_dir(&self) -> bool {
            self.is(libc::S_IFDIR)
        }
        pub fn is_file(&self) -> bool {
            self.is(libc::S_IFREG)
        }
        pub fn is_symlink(&self) -> bool {
            self.is(libc::S_IFLNK)
        }

        pub fn is(&self, mode: mode_t) -> bool {
            self.mode & libc::S_IFMT == mode
        }
    }

    impl FromInner<u32> for FilePermissions {
        fn from_inner(mode: u32) -> FilePermissions {
            FilePermissions { mode: mode as mode_t }
        }
    }

    impl fmt::Debug for ReadDir {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            // This will only be called from std::fs::ReadDir, which will add a "ReadDir()" frame.
            // Thus the result will be e g 'ReadDir("/home")'
            fmt::Debug::fmt(&*self.inner.root, f)
        }
    }

    impl Iterator for ReadDir {
        type Item = io::Result<DirEntry>;

        #[cfg(any(
            target_os = "solaris",
            target_os = "fuchsia",
            target_os = "redox",
            target_os = "illumos"
        ))]
        fn next(&mut self) -> Option<io::Result<DirEntry>> {
            use crate::slice;

            unsafe {
                loop {
                    // Although readdir_r(3) would be a correct function to use here because
                    // of the thread safety, on Illumos and Fuchsia the readdir(3C) function
                    // is safe to use in threaded applications and it is generally preferred
                    // over the readdir_r(3C) function.
                    super::os::set_errno(0);
                    let entry_ptr = libc::readdir(self.inner.dirp.0);
                    if entry_ptr.is_null() {
                        // NULL can mean either the end is reached or an error occurred.
                        // So we had to clear errno beforehand to check for an error now.
                        return match super::os::errno() {
                            0 => None,
                            e => Some(Err(Error::from_raw_os_error(e))),
                        };
                    }

                    let name = (*entry_ptr).d_name.as_ptr();
                    let namelen = libc::strlen(name) as usize;

                    let ret = DirEntry {
                        entry: *entry_ptr,
                        name: slice::from_raw_parts(name as *const u8, namelen as usize)
                            .to_owned()
                            .into_boxed_slice(),
                        dir: self.clone(),
                    };
                    if ret.name_bytes() != b"." && ret.name_bytes() != b".." {
                        return Some(Ok(ret));
                    }
                }
            }
        }

        #[cfg(not(any(
            target_os = "solaris",
            target_os = "fuchsia",
            target_os = "redox",
            target_os = "illumos"
        )))]
        fn next(&mut self) -> Option<io::Result<DirEntry>> {
            if self.end_of_stream {
                return None;
            }

            unsafe {
                let mut ret = DirEntry { entry: mem::zeroed(), dir: self.clone() };
                let mut entry_ptr = ptr::null_mut();
                loop {
                    if readdir64_r(self.inner.dirp.0, &mut ret.entry, &mut entry_ptr) != 0 {
                        if entry_ptr.is_null() {
                            // We encountered an error (which will be returned in this iteration), but
                            // we also reached the end of the directory stream. The `end_of_stream`
                            // flag is enabled to make sure that we return `None` in the next iteration
                            // (instead of looping forever)
                            self.end_of_stream = true;
                        }
                        return Some(Err(Error::last_os_error()));
                    }
                    if entry_ptr.is_null() {
                        return None;
                    }
                    if ret.name_bytes() != b"." && ret.name_bytes() != b".." {
                        return Some(Ok(ret));
                    }
                }
            }
        }
    }

    impl Drop for Dir {
        fn drop(&mut self) {
            let r = unsafe { libc::closedir(self.0) };
            debug_assert_eq!(r, 0);
        }
    }

    impl DirEntry {
        pub fn path(&self) -> PathBuf {
            self.dir.inner.root.join(OsStr::from_bytes(self.name_bytes()))
        }

        pub fn file_name(&self) -> OsString {
            OsStr::from_bytes(self.name_bytes()).to_os_string()
        }

        #[cfg(any(target_os = "linux", target_os = "emscripten", target_os = "android"))]
        pub fn metadata(&self) -> io::Result<FileAttr> {
            let fd = cvt(unsafe { dirfd(self.dir.inner.dirp.0) })?;
            let name = self.entry.d_name.as_ptr();

            cfg_has_statx! {
                if let Some(ret) = unsafe { try_statx(
                    fd,
                    name,
                    libc::AT_SYMLINK_NOFOLLOW | libc::AT_STATX_SYNC_AS_STAT,
                    libc::STATX_ALL,
                ) } {
                    return ret;
                }
            }

            let mut stat: stat64 = unsafe { mem::zeroed() };
            cvt(unsafe { fstatat64(fd, name, &mut stat, libc::AT_SYMLINK_NOFOLLOW) })?;
            Ok(FileAttr::from_stat64(stat))
        }

        #[cfg(not(any(target_os = "linux", target_os = "emscripten", target_os = "android")))]
        pub fn metadata(&self) -> io::Result<FileAttr> {
            lstat(&self.path())
        }

        #[cfg(any(target_os = "solaris", target_os = "illumos", target_os = "haiku"))]
        pub fn file_type(&self) -> io::Result<FileType> {
            lstat(&self.path()).map(|m| m.file_type())
        }

        #[cfg(not(any(target_os = "solaris", target_os = "illumos", target_os = "haiku")))]
        pub fn file_type(&self) -> io::Result<FileType> {
            match self.entry.d_type {
                libc::DT_CHR => Ok(FileType { mode: libc::S_IFCHR }),
                libc::DT_FIFO => Ok(FileType { mode: libc::S_IFIFO }),
                libc::DT_LNK => Ok(FileType { mode: libc::S_IFLNK }),
                libc::DT_REG => Ok(FileType { mode: libc::S_IFREG }),
                libc::DT_SOCK => Ok(FileType { mode: libc::S_IFSOCK }),
                libc::DT_DIR => Ok(FileType { mode: libc::S_IFDIR }),
                libc::DT_BLK => Ok(FileType { mode: libc::S_IFBLK }),
                _ => lstat(&self.path()).map(|m| m.file_type()),
            }
        }

        #[cfg(any(
            target_os = "macos",
            target_os = "ios",
            target_os = "linux",
            target_os = "emscripten",
            target_os = "android",
            target_os = "solaris",
            target_os = "illumos",
            target_os = "haiku",
            target_os = "l4re",
            target_os = "fuchsia",
            target_os = "redox"
        ))]
        pub fn ino(&self) -> u64 {
            self.entry.d_ino as u64
        }

        #[cfg(any(
            target_os = "freebsd",
            target_os = "openbsd",
            target_os = "netbsd",
            target_os = "dragonfly"
        ))]
        pub fn ino(&self) -> u64 {
            self.entry.d_fileno as u64
        }

        #[cfg(any(
            target_os = "macos",
            target_os = "ios",
            target_os = "netbsd",
            target_os = "openbsd",
            target_os = "freebsd",
            target_os = "dragonfly"
        ))]
        fn name_bytes(&self) -> &[u8] {
            use crate::slice;
            unsafe {
                slice::from_raw_parts(
                    self.entry.d_name.as_ptr() as *const u8,
                    self.entry.d_namlen as usize,
                )
            }
        }
        #[cfg(any(
            target_os = "android",
            target_os = "linux",
            target_os = "emscripten",
            target_os = "l4re",
            target_os = "haiku"
        ))]
        fn name_bytes(&self) -> &[u8] {
            unsafe { CStr::from_ptr(self.entry.d_name.as_ptr()).to_bytes() }
        }
        #[cfg(any(
            target_os = "solaris",
            target_os = "illumos",
            target_os = "fuchsia",
            target_os = "redox"
        ))]
        fn name_bytes(&self) -> &[u8] {
            &*self.name
        }
    }

    impl OpenOptions {
        pub fn new() -> OpenOptions {
            OpenOptions {
                // generic
                read: false,
                write: false,
                append: false,
                truncate: false,
                create: false,
                create_new: false,
                // system-specific
                custom_flags: 0,
                mode: 0o666,
            }
        }

        pub fn read(&mut self, read: bool) {
            self.read = read;
        }
        pub fn write(&mut self, write: bool) {
            self.write = write;
        }
        pub fn append(&mut self, append: bool) {
            self.append = append;
        }
        pub fn truncate(&mut self, truncate: bool) {
            self.truncate = truncate;
        }
        pub fn create(&mut self, create: bool) {
            self.create = create;
        }
        pub fn create_new(&mut self, create_new: bool) {
            self.create_new = create_new;
        }

        pub fn custom_flags(&mut self, flags: i32) {
            self.custom_flags = flags;
        }
        pub fn mode(&mut self, mode: u32) {
            self.mode = mode as mode_t;
        }

        fn get_access_mode(&self) -> io::Result<c_int> {
            match (self.read, self.write, self.append) {
                (true, false, false) => Ok(libc::O_RDONLY),
                (false, true, false) => Ok(libc::O_WRONLY),
                (true, true, false) => Ok(libc::O_RDWR),
                (false, _, true) => Ok(libc::O_WRONLY | libc::O_APPEND),
                (true, _, true) => Ok(libc::O_RDWR | libc::O_APPEND),
                (false, false, false) => Err(Error::from_raw_os_error(libc::EINVAL)),
            }
        }

        fn get_creation_mode(&self) -> io::Result<c_int> {
            match (self.write, self.append) {
                (true, false) => {}
                (false, false) => {
                    if self.truncate || self.create || self.create_new {
                        return Err(Error::from_raw_os_error(libc::EINVAL));
                    }
                }
                (_, true) => {
                    if self.truncate && !self.create_new {
                        return Err(Error::from_raw_os_error(libc::EINVAL));
                    }
                }
            }

            Ok(match (self.create, self.truncate, self.create_new) {
                (false, false, false) => 0,
                (true, false, false) => libc::O_CREAT,
                (false, true, false) => libc::O_TRUNC,
                (true, true, false) => libc::O_CREAT | libc::O_TRUNC,
                (_, _, true) => libc::O_CREAT | libc::O_EXCL,
            })
        }
    }

    impl File {
        pub fn open(path: &Path, opts: &OpenOptions) -> io::Result<File> {
            let path = cstr(path)?;
            File::open_c(&path, opts)
        }

        pub fn open_c(path: &CStr, opts: &OpenOptions) -> io::Result<File> {
            let flags = libc::O_CLOEXEC
                | opts.get_access_mode()?
                | opts.get_creation_mode()?
                | (opts.custom_flags as c_int & !libc::O_ACCMODE);
            // The third argument of `open64` is documented to have type `mode_t`. On
            // some platforms (like macOS, where `open64` is actually `open`), `mode_t` is `u16`.
            // However, since this is a variadic function, C integer promotion rules mean that on
            // the ABI level, this still gets passed as `c_int` (aka `u32` on Unix platforms).
            let fd = cvt_r(|| unsafe { open64(path.as_ptr(), flags, opts.mode as c_int) })?;
            Ok(File(FileDesc::new(fd)))
        }

        pub fn file_attr(&self) -> io::Result<FileAttr> {
            let fd = self.0.raw();

            cfg_has_statx! {
                if let Some(ret) = unsafe { try_statx(
                    fd,
                    b"\0" as *const _ as *const libc::c_char,
                    libc::AT_EMPTY_PATH | libc::AT_STATX_SYNC_AS_STAT,
                    libc::STATX_ALL,
                ) } {
                    return ret;
                }
            }

            let mut stat: stat64 = unsafe { mem::zeroed() };
            cvt(unsafe { fstat64(fd, &mut stat) })?;
            Ok(FileAttr::from_stat64(stat))
        }

        pub fn fsync(&self) -> io::Result<()> {
            cvt_r(|| unsafe { os_fsync(self.0.raw()) })?;
            return Ok(());

            #[cfg(any(target_os = "macos", target_os = "ios"))]
            unsafe fn os_fsync(fd: c_int) -> c_int {
                libc::fcntl(fd, libc::F_FULLFSYNC)
            }
            #[cfg(not(any(target_os = "macos", target_os = "ios")))]
            unsafe fn os_fsync(fd: c_int) -> c_int {
                libc::fsync(fd)
            }
        }

        pub fn datasync(&self) -> io::Result<()> {
            cvt_r(|| unsafe { os_datasync(self.0.raw()) })?;
            return Ok(());

            #[cfg(any(target_os = "macos", target_os = "ios"))]
            unsafe fn os_datasync(fd: c_int) -> c_int {
                libc::fcntl(fd, libc::F_FULLFSYNC)
            }
            #[cfg(target_os = "linux")]
            unsafe fn os_datasync(fd: c_int) -> c_int {
                libc::fdatasync(fd)
            }
            #[cfg(not(any(target_os = "macos", target_os = "ios", target_os = "linux")))]
            unsafe fn os_datasync(fd: c_int) -> c_int {
                libc::fsync(fd)
            }
        }

        pub fn truncate(&self, size: u64) -> io::Result<()> {
            #[cfg(target_os = "android")]
            return crate::sys::android::ftruncate64(self.0.raw(), size);

            #[cfg(not(target_os = "android"))]
            {
                use crate::convert::TryInto;
                let size: off64_t =
                    size.try_into().map_err(|e| io::Error::new(io::ErrorKind::InvalidInput, e))?;
                cvt_r(|| unsafe { ftruncate64(self.0.raw(), size) }).map(drop)
            }
        }

        pub fn read(&self, buf: &mut [u8]) -> io::Result<usize> {
            self.0.read(buf)
        }

        pub fn read_vectored(&self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
            self.0.read_vectored(bufs)
        }

        #[inline]
        pub fn is_read_vectored(&self) -> bool {
            self.0.is_read_vectored()
        }

        pub fn read_at(&self, buf: &mut [u8], offset: u64) -> io::Result<usize> {
            self.0.read_at(buf, offset)
        }

        pub fn write(&self, buf: &[u8]) -> io::Result<usize> {
            self.0.write(buf)
        }

        pub fn write_vectored(&self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
            self.0.write_vectored(bufs)
        }

        #[inline]
        pub fn is_write_vectored(&self) -> bool {
            self.0.is_write_vectored()
        }

        pub fn write_at(&self, buf: &[u8], offset: u64) -> io::Result<usize> {
            self.0.write_at(buf, offset)
        }

        pub fn flush(&self) -> io::Result<()> {
            Ok(())
        }

        pub fn seek(&self, pos: SeekFrom) -> io::Result<u64> {
            let (whence, pos) = match pos {
                // Casting to `i64` is fine, too large values will end up as
                // negative which will cause an error in `lseek64`.
                SeekFrom::Start(off) => (libc::SEEK_SET, off as i64),
                SeekFrom::End(off) => (libc::SEEK_END, off),
                SeekFrom::Current(off) => (libc::SEEK_CUR, off),
            };
            let n = cvt(unsafe { lseek64(self.0.raw(), pos, whence) })?;
            Ok(n as u64)
        }

        pub fn duplicate(&self) -> io::Result<File> {
            self.0.duplicate().map(File)
        }

        pub fn fd(&self) -> &FileDesc {
            &self.0
        }

        pub fn into_fd(self) -> FileDesc {
            self.0
        }

        pub fn set_permissions(&self, perm: FilePermissions) -> io::Result<()> {
            cvt_r(|| unsafe { libc::fchmod(self.0.raw(), perm.mode) })?;
            Ok(())
        }
    }

    impl DirBuilder {
        pub fn new() -> DirBuilder {
            DirBuilder { mode: 0o777 }
        }

        pub fn mkdir(&self, p: &Path) -> io::Result<()> {
            let p = cstr(p)?;
            cvt(unsafe { libc::mkdir(p.as_ptr(), self.mode) })?;
            Ok(())
        }

        pub fn set_mode(&mut self, mode: u32) {
            self.mode = mode as mode_t;
        }
    }

    fn cstr(path: &Path) -> io::Result<CString> {
        Ok(CString::new(path.as_os_str().as_bytes())?)
    }

    impl FromInner<c_int> for File {
        fn from_inner(fd: c_int) -> File {
            File(FileDesc::new(fd))
        }
    }

    impl fmt::Debug for File {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            #[cfg(target_os = "linux")]
            fn get_path(fd: c_int) -> Option<PathBuf> {
                let mut p = PathBuf::from("/proc/self/fd");
                p.push(&fd.to_string());
                readlink(&p).ok()
            }

            #[cfg(target_os = "macos")]
            fn get_path(fd: c_int) -> Option<PathBuf> {
                // FIXME: The use of PATH_MAX is generally not encouraged, but it
                // is inevitable in this case because macOS defines `fcntl` with
                // `F_GETPATH` in terms of `MAXPATHLEN`, and there are no
                // alternatives. If a better method is invented, it should be used
                // instead.
                let mut buf = vec![0; libc::PATH_MAX as usize];
                let n = unsafe { libc::fcntl(fd, libc::F_GETPATH, buf.as_ptr()) };
                if n == -1 {
                    return None;
                }
                let l = buf.iter().position(|&c| c == 0).unwrap();
                buf.truncate(l as usize);
                buf.shrink_to_fit();
                Some(PathBuf::from(OsString::from_vec(buf)))
            }

            #[cfg(not(any(target_os = "linux", target_os = "macos")))]
            fn get_path(_fd: c_int) -> Option<PathBuf> {
                // FIXME(#24570): implement this for other Unix platforms
                None
            }

            #[cfg(any(target_os = "linux", target_os = "macos"))]
            fn get_mode(fd: c_int) -> Option<(bool, bool)> {
                let mode = unsafe { libc::fcntl(fd, libc::F_GETFL) };
                if mode == -1 {
                    return None;
                }
                match mode & libc::O_ACCMODE {
                    libc::O_RDONLY => Some((true, false)),
                    libc::O_RDWR => Some((true, true)),
                    libc::O_WRONLY => Some((false, true)),
                    _ => None,
                }
            }

            #[cfg(not(any(target_os = "linux", target_os = "macos")))]
            fn get_mode(_fd: c_int) -> Option<(bool, bool)> {
                // FIXME(#24570): implement this for other Unix platforms
                None
            }

            let fd = self.0.raw();
            let mut b = f.debug_struct("File");
            b.field("fd", &fd);
            if let Some(path) = get_path(fd) {
                b.field("path", &path);
            }
            if let Some((read, write)) = get_mode(fd) {
                b.field("read", &read).field("write", &write);
            }
            b.finish()
        }
    }

    pub fn readdir(p: &Path) -> io::Result<ReadDir> {
        let root = p.to_path_buf();
        let p = cstr(p)?;
        unsafe {
            let ptr = libc::opendir(p.as_ptr());
            if ptr.is_null() {
                Err(Error::last_os_error())
            } else {
                let inner = InnerReadDir { dirp: Dir(ptr), root };
                Ok(ReadDir { inner: Arc::new(inner), end_of_stream: false })
            }
        }
    }

    pub fn unlink(p: &Path) -> io::Result<()> {
        let p = cstr(p)?;
        cvt(unsafe { libc::unlink(p.as_ptr()) })?;
        Ok(())
    }

    pub fn rename(old: &Path, new: &Path) -> io::Result<()> {
        let old = cstr(old)?;
        let new = cstr(new)?;
        cvt(unsafe { libc::rename(old.as_ptr(), new.as_ptr()) })?;
        Ok(())
    }

    pub fn set_perm(p: &Path, perm: FilePermissions) -> io::Result<()> {
        let p = cstr(p)?;
        cvt_r(|| unsafe { libc::chmod(p.as_ptr(), perm.mode) })?;
        Ok(())
    }

    pub fn rmdir(p: &Path) -> io::Result<()> {
        let p = cstr(p)?;
        cvt(unsafe { libc::rmdir(p.as_ptr()) })?;
        Ok(())
    }

    pub fn readlink(p: &Path) -> io::Result<PathBuf> {
        let c_path = cstr(p)?;
        let p = c_path.as_ptr();

        let mut buf = Vec::with_capacity(256);

        loop {
            let buf_read =
                cvt(unsafe { libc::readlink(p, buf.as_mut_ptr() as *mut _, buf.capacity()) })? as usize;

            unsafe {
                buf.set_len(buf_read);
            }

            if buf_read != buf.capacity() {
                buf.shrink_to_fit();

                return Ok(PathBuf::from(OsString::from_vec(buf)));
            }

            // Trigger the internal buffer resizing logic of `Vec` by requiring
            // more space than the current capacity. The length is guaranteed to be
            // the same as the capacity due to the if statement above.
            buf.reserve(1);
        }
    }

    pub fn symlink(src: &Path, dst: &Path) -> io::Result<()> {
        let src = cstr(src)?;
        let dst = cstr(dst)?;
        cvt(unsafe { libc::symlink(src.as_ptr(), dst.as_ptr()) })?;
        Ok(())
    }

    pub fn link(src: &Path, dst: &Path) -> io::Result<()> {
        let src = cstr(src)?;
        let dst = cstr(dst)?;
        cvt(unsafe { libc::link(src.as_ptr(), dst.as_ptr()) })?;
        Ok(())
    }

    pub fn stat(p: &Path) -> io::Result<FileAttr> {
        let p = cstr(p)?;

        cfg_has_statx! {
            if let Some(ret) = unsafe { try_statx(
                libc::AT_FDCWD,
                p.as_ptr(),
                libc::AT_STATX_SYNC_AS_STAT,
                libc::STATX_ALL,
            ) } {
                return ret;
            }
        }

        let mut stat: stat64 = unsafe { mem::zeroed() };
        cvt(unsafe { stat64(p.as_ptr(), &mut stat) })?;
        Ok(FileAttr::from_stat64(stat))
    }

    pub fn lstat(p: &Path) -> io::Result<FileAttr> {
        let p = cstr(p)?;

        cfg_has_statx! {
            if let Some(ret) = unsafe { try_statx(
                libc::AT_FDCWD,
                p.as_ptr(),
                libc::AT_SYMLINK_NOFOLLOW | libc::AT_STATX_SYNC_AS_STAT,
                libc::STATX_ALL,
            ) } {
                return ret;
            }
        }

        let mut stat: stat64 = unsafe { mem::zeroed() };
        cvt(unsafe { lstat64(p.as_ptr(), &mut stat) })?;
        Ok(FileAttr::from_stat64(stat))
    }

    pub fn canonicalize(p: &Path) -> io::Result<PathBuf> {
        let path = CString::new(p.as_os_str().as_bytes())?;
        let buf;
        unsafe {
            let r = libc::realpath(path.as_ptr(), ptr::null_mut());
            if r.is_null() {
                return Err(io::Error::last_os_error());
            }
            buf = CStr::from_ptr(r).to_bytes().to_vec();
            libc::free(r as *mut _);
        }
        Ok(PathBuf::from(OsString::from_vec(buf)))
    }

    fn open_from(from: &Path) -> io::Result<(crate::fs::File, crate::fs::Metadata)> {
        use crate::fs::File;

        let reader = File::open(from)?;
        let metadata = reader.metadata()?;
        if !metadata.is_file() {
            return Err(Error::new(
                ErrorKind::InvalidInput,
                "the source path is not an existing regular file",
            ));
        }
        Ok((reader, metadata))
    }

    fn open_to_and_set_permissions(
        to: &Path,
        reader_metadata: crate::fs::Metadata,
    ) -> io::Result<(crate::fs::File, crate::fs::Metadata)> {
        use crate::fs::OpenOptions;
        use crate::os::unix::fs::{OpenOptionsExt, PermissionsExt};

        let perm = reader_metadata.permissions();
        let writer = OpenOptions::new()
            // create the file with the correct mode right away
            .mode(perm.mode())
            .write(true)
            .create(true)
            .truncate(true)
            .open(to)?;
        let writer_metadata = writer.metadata()?;
        if writer_metadata.is_file() {
            // Set the correct file permissions, in case the file already existed.
            // Don't set the permissions on already existing non-files like
            // pipes/FIFOs or device nodes.
            writer.set_permissions(perm)?;
        }
        Ok((writer, writer_metadata))
    }

    #[cfg(not(any(
        target_os = "linux",
        target_os = "android",
        target_os = "macos",
        target_os = "ios"
    )))]
    pub fn copy(from: &Path, to: &Path) -> io::Result<u64> {
        let (mut reader, reader_metadata) = open_from(from)?;
        let (mut writer, _) = open_to_and_set_permissions(to, reader_metadata)?;

        io::copy(&mut reader, &mut writer)
    }

    #[cfg(any(target_os = "linux", target_os = "android"))]
    pub fn copy(from: &Path, to: &Path) -> io::Result<u64> {
        use crate::cmp;
        use crate::sync::atomic::{AtomicBool, Ordering};

        // Kernel prior to 4.5 don't have copy_file_range
        // We store the availability in a global to avoid unnecessary syscalls
        static HAS_COPY_FILE_RANGE: AtomicBool = AtomicBool::new(true);

        unsafe fn copy_file_range(
            fd_in: libc::c_int,
            off_in: *mut libc::loff_t,
            fd_out: libc::c_int,
            off_out: *mut libc::loff_t,
            len: libc::size_t,
            flags: libc::c_uint,
        ) -> libc::c_long {
            libc::syscall(libc::SYS_copy_file_range, fd_in, off_in, fd_out, off_out, len, flags)
        }

        let (mut reader, reader_metadata) = open_from(from)?;
        let max_len = u64::MAX;
        let (mut writer, _) = open_to_and_set_permissions(to, reader_metadata)?;

        let has_copy_file_range = HAS_COPY_FILE_RANGE.load(Ordering::Relaxed);
        let mut written = 0u64;
        while written < max_len {
            let copy_result = if has_copy_file_range {
                let bytes_to_copy = cmp::min(max_len - written, usize::MAX as u64) as usize;
                let copy_result = unsafe {
                    // We actually don't have to adjust the offsets,
                    // because copy_file_range adjusts the file offset automatically
                    cvt(copy_file_range(
                        reader.as_raw_fd(),
                        ptr::null_mut(),
                        writer.as_raw_fd(),
                        ptr::null_mut(),
                        bytes_to_copy,
                        0,
                    ))
                };
                if let Err(ref copy_err) = copy_result {
                    match copy_err.raw_os_error() {
                        Some(libc::ENOSYS | libc::EPERM | libc::EOPNOTSUPP) => {
                            HAS_COPY_FILE_RANGE.store(false, Ordering::Relaxed);
                        }
                        _ => {}
                    }
                }
                copy_result
            } else {
                Err(io::Error::from_raw_os_error(libc::ENOSYS))
            };
            match copy_result {
                Ok(0) if written == 0 => {
                    // fallback to work around several kernel bugs where copy_file_range will fail to
                    // copy any bytes and return 0 instead of an error if
                    // - reading virtual files from the proc filesystem which appear to have 0 size
                    //   but are not empty. noted in coreutils to affect kernels at least up to 5.6.19.
                    // - copying from an overlay filesystem in docker. reported to occur on fedora 32.
                    return io::copy(&mut reader, &mut writer);
                }
                Ok(0) => return Ok(written), // reached EOF
                Ok(ret) => written += ret as u64,
                Err(err) => {
                    match err.raw_os_error() {
                        Some(
                            libc::ENOSYS | libc::EXDEV | libc::EINVAL | libc::EPERM | libc::EOPNOTSUPP,
                        ) => {
                            // Try fallback io::copy if either:
                            // - Kernel version is < 4.5 (ENOSYS)
                            // - Files are mounted on different fs (EXDEV)
                            // - copy_file_range is broken in various ways on RHEL/CentOS 7 (EOPNOTSUPP)
                            // - copy_file_range is disallowed, for example by seccomp (EPERM)
                            // - copy_file_range cannot be used with pipes or device nodes (EINVAL)
                            assert_eq!(written, 0);
                            return io::copy(&mut reader, &mut writer);
                        }
                        _ => return Err(err),
                    }
                }
            }
        }
        Ok(written)
    }

    #[cfg(any(target_os = "macos", target_os = "ios"))]
    pub fn copy(from: &Path, to: &Path) -> io::Result<u64> {
        use crate::sync::atomic::{AtomicBool, Ordering};

        const COPYFILE_ACL: u32 = 1 << 0;
        const COPYFILE_STAT: u32 = 1 << 1;
        const COPYFILE_XATTR: u32 = 1 << 2;
        const COPYFILE_DATA: u32 = 1 << 3;

        const COPYFILE_SECURITY: u32 = COPYFILE_STAT | COPYFILE_ACL;
        const COPYFILE_METADATA: u32 = COPYFILE_SECURITY | COPYFILE_XATTR;
        const COPYFILE_ALL: u32 = COPYFILE_METADATA | COPYFILE_DATA;

        const COPYFILE_STATE_COPIED: u32 = 8;

        #[allow(non_camel_case_types)]
        type copyfile_state_t = *mut libc::c_void;
        #[allow(non_camel_case_types)]
        type copyfile_flags_t = u32;

        extern "C" {
            fn fcopyfile(
                from: libc::c_int,
                to: libc::c_int,
                state: copyfile_state_t,
                flags: copyfile_flags_t,
            ) -> libc::c_int;
            fn copyfile_state_alloc() -> copyfile_state_t;
            fn copyfile_state_free(state: copyfile_state_t) -> libc::c_int;
            fn copyfile_state_get(
                state: copyfile_state_t,
                flag: u32,
                dst: *mut libc::c_void,
            ) -> libc::c_int;
        }

        struct FreeOnDrop(copyfile_state_t);
        impl Drop for FreeOnDrop {
            fn drop(&mut self) {
                // The code below ensures that `FreeOnDrop` is never a null pointer
                unsafe {
                    // `copyfile_state_free` returns -1 if the `to` or `from` files
                    // cannot be closed. However, this is not considered this an
                    // error.
                    copyfile_state_free(self.0);
                }
            }
        }

        // MacOS prior to 10.12 don't support `fclonefileat`
        // We store the availability in a global to avoid unnecessary syscalls
        static HAS_FCLONEFILEAT: AtomicBool = AtomicBool::new(true);
        syscall! {
            fn fclonefileat(
                srcfd: libc::c_int,
                dst_dirfd: libc::c_int,
                dst: *const libc::c_char,
                flags: libc::c_int
            ) -> libc::c_int
        }

        let (reader, reader_metadata) = open_from(from)?;

        // Opportunistically attempt to create a copy-on-write clone of `from`
        // using `fclonefileat`.
        if HAS_FCLONEFILEAT.load(Ordering::Relaxed) {
            let to = cstr(to)?;
            let clonefile_result =
                cvt(unsafe { fclonefileat(reader.as_raw_fd(), libc::AT_FDCWD, to.as_ptr(), 0) });
            match clonefile_result {
                Ok(_) => return Ok(reader_metadata.len()),
                Err(err) => match err.raw_os_error() {
                    // `fclonefileat` will fail on non-APFS volumes, if the
                    // destination already exists, or if the source and destination
                    // are on different devices. In all these cases `fcopyfile`
                    // should succeed.
                    Some(libc::ENOTSUP) | Some(libc::EEXIST) | Some(libc::EXDEV) => (),
                    Some(libc::ENOSYS) => HAS_FCLONEFILEAT.store(false, Ordering::Relaxed),
                    _ => return Err(err),
                },
            }
        }

        // Fall back to using `fcopyfile` if `fclonefileat` does not succeed.
        let (writer, writer_metadata) = open_to_and_set_permissions(to, reader_metadata)?;

        // We ensure that `FreeOnDrop` never contains a null pointer so it is
        // always safe to call `copyfile_state_free`
        let state = unsafe {
            let state = copyfile_state_alloc();
            if state.is_null() {
                return Err(crate::io::Error::last_os_error());
            }
            FreeOnDrop(state)
        };

        let flags = if writer_metadata.is_file() { COPYFILE_ALL } else { COPYFILE_DATA };

        cvt(unsafe { fcopyfile(reader.as_raw_fd(), writer.as_raw_fd(), state.0, flags) })?;

        let mut bytes_copied: libc::off_t = 0;
        cvt(unsafe {
            copyfile_state_get(
                state.0,
                COPYFILE_STATE_COPIED,
                &mut bytes_copied as *mut libc::off_t as *mut libc::c_void,
            )
        })?;
        Ok(bytes_copied as u64)
    }