sysdeps/unix/sysv/linux/pathconf.c

   1 /* Get file-specific information about a file.  Linux version.
   2    Copyright (C) 1991-2024 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <errno.h>
  20 #include <mntent.h>
  21 #include <stdio_ext.h>
  22 #include <string.h>
  23 #include <unistd.h>
  24 #include <sys/sysmacros.h>
  25
  26 #include "pathconf.h"
  27 #include "linux_fsinfo.h"
  28 #include <not-cancel.h>
  29
  30 static long int posix_pathconf (const char *file, int name);
  31
  32 /* Define this first, so it can be inlined.  */
  33 #define __pathconf static posix_pathconf
  34 #include <sysdeps/posix/pathconf.c>
  35
  36
  37 /* Get file-specific information about FILE.  */
  38 long int
  39 __pathconf (const char *file, int name)
  40 {
  41   struct statfs fsbuf;
  42
  43   switch (name)
  44     {
  45     case _PC_LINK_MAX:
  46       return __statfs_link_max (__statfs (file, &fsbuf), &fsbuf, file, -1);
  47
  48     case _PC_FILESIZEBITS:
  49       return __statfs_filesize_max (__statfs (file, &fsbuf), &fsbuf);
  50
  51     case _PC_2_SYMLINKS:
  52       return __statfs_symlinks (__statfs (file, &fsbuf), &fsbuf);
  53
  54     case _PC_CHOWN_RESTRICTED:
  55       return __statfs_chown_restricted (__statfs (file, &fsbuf), &fsbuf);
  56
  57     default:
  58       return posix_pathconf (file, name);
  59     }
  60 }
  61
  62
  63 static long int
  64 distinguish_extX (const struct statfs *fsbuf, const char *file, int fd)
  65 {
  66   char buf[64];
  67   char path[PATH_MAX];
  68   struct __stat64_t64 st;
  69
  70   if ((file == NULL ? __fstat64_time64 (fd, &st)
  71                     : __stat64_time64 (file, &st)) != 0)
  72     /* Strange.  The statfd call worked, but stat fails.  Default to
  73        the more pessimistic value.  */
  74     return EXT2_LINK_MAX;
  75
  76   __snprintf (buf, sizeof (buf), "/sys/dev/block/%u:%u",
  77               __gnu_dev_major (st.st_dev), __gnu_dev_minor (st.st_dev));
  78
  79   ssize_t n = __readlink (buf, path, sizeof (path));
  80   if (n != -1 && n < sizeof (path))
  81     {
  82       path[n] = '\0';
  83       char *base = strdupa (__basename (path));
  84       __snprintf (path, sizeof (path), "/sys/fs/ext4/%s", base);
  85
  86       return __access (path, F_OK) == 0 ? EXT4_LINK_MAX : EXT2_LINK_MAX;
  87     }
  88
  89   /* XXX Is there a better way to distinguish ext2/3 from ext4 than
  90      iterating over the mounted filesystems and compare the device
  91      numbers?  */
  92   FILE *mtab = __setmntent ("/proc/mounts", "r");
  93   if (mtab == NULL)
  94     mtab = __setmntent (_PATH_MOUNTED, "r");
  95
  96   /* By default be conservative.  */
  97   long int result = EXT2_LINK_MAX;
  98   if (mtab != NULL)
  99     {
 100       struct mntent mntbuf;
 101       char tmpbuf[1024];
 102
 103       /* No locking needed.  */
 104       (void) __fsetlocking (mtab, FSETLOCKING_BYCALLER);
 105
 106       while (__getmntent_r (mtab, &mntbuf, tmpbuf, sizeof (tmpbuf)))
 107         {
 108           if (strcmp (mntbuf.mnt_type, "ext2") != 0
 109               && strcmp (mntbuf.mnt_type, "ext3") != 0
 110               && strcmp (mntbuf.mnt_type, "ext4") != 0)
 111             continue;
 112
 113           struct __stat64_t64 fsst;
 114           if (__stat64_time64 (mntbuf.mnt_dir, &fsst) >= 0
 115               && st.st_dev == fsst.st_dev)
 116             {
 117               if (strcmp (mntbuf.mnt_type, "ext4") == 0)
 118                 result = EXT4_LINK_MAX;
 119               break;
 120             }
 121         }
 122
 123       /* Close the file.  */
 124       __endmntent (mtab);
 125     }
 126
 127   return result;
 128 }
 129
 130
 131 /* Used like: return statfs_link_max (__statfs (name, &buf), &buf); */
 132 long int
 133 __statfs_link_max (int result, const struct statfs *fsbuf, const char *file,
 134                    int fd)
 135 {
 136   if (result < 0)
 137     {
 138       if (errno == ENOSYS)
 139         /* Not possible, return the default value.  */
 140         return LINUX_LINK_MAX;
 141
 142       /* Some error occurred.  */
 143       return -1;
 144     }
 145
 146   switch (fsbuf->f_type)
 147     {
 148     case EXT2_SUPER_MAGIC:
 149       /* Unfortunately the kernel does not return a different magic number
 150          for ext4.  This would be necessary to easily detect etx4 since it
 151          has a different LINK_MAX value.  Therefore we have to find it out
 152          the hard way.  */
 153       return distinguish_extX (fsbuf, file, fd);
 154
 155     case F2FS_SUPER_MAGIC:
 156       return F2FS_LINK_MAX;
 157
 158     case MINIX_SUPER_MAGIC:
 159     case MINIX_SUPER_MAGIC2:
 160       return MINIX_LINK_MAX;
 161
 162     case MINIX2_SUPER_MAGIC:
 163     case MINIX2_SUPER_MAGIC2:
 164       return MINIX2_LINK_MAX;
 165
 166     case XENIX_SUPER_MAGIC:
 167       return XENIX_LINK_MAX;
 168
 169     case SYSV4_SUPER_MAGIC:
 170     case SYSV2_SUPER_MAGIC:
 171       return SYSV_LINK_MAX;
 172
 173     case COH_SUPER_MAGIC:
 174       return COH_LINK_MAX;
 175
 176     case UFS_MAGIC:
 177     case UFS_CIGAM:
 178       return UFS_LINK_MAX;
 179
 180     case REISERFS_SUPER_MAGIC:
 181       return REISERFS_LINK_MAX;
 182
 183     case XFS_SUPER_MAGIC:
 184       return XFS_LINK_MAX;
 185
 186     case LUSTRE_SUPER_MAGIC:
 187       return LUSTRE_LINK_MAX;
 188
 189     default:
 190       return LINUX_LINK_MAX;
 191     }
 192 }
 193
 194
 195 /* Used like: return statfs_filesize_max (__statfs (name, &buf), &buf); */
 196 long int
 197 __statfs_filesize_max (int result, const struct statfs *fsbuf)
 198 {
 199   if (result < 0)
 200     {
 201       if (errno == ENOSYS)
 202         /* Not possible, return the default value.  */
 203         return 32;
 204
 205       /* Some error occurred.  */
 206       return -1;
 207     }
 208
 209   switch (fsbuf->f_type)
 210     {
 211     case F2FS_SUPER_MAGIC:
 212       return 256;
 213
 214     case BTRFS_SUPER_MAGIC:
 215       return 255;
 216
 217     case EXT2_SUPER_MAGIC:
 218     case UFS_MAGIC:
 219     case UFS_CIGAM:
 220     case REISERFS_SUPER_MAGIC:
 221     case XFS_SUPER_MAGIC:
 222     case SMB_SUPER_MAGIC:
 223     case NTFS_SUPER_MAGIC:
 224     case UDF_SUPER_MAGIC:
 225     case JFS_SUPER_MAGIC:
 226     case VXFS_SUPER_MAGIC:
 227     case CGROUP_SUPER_MAGIC:
 228     case LUSTRE_SUPER_MAGIC:
 229       return 64;
 230
 231     case MSDOS_SUPER_MAGIC:
 232     case JFFS_SUPER_MAGIC:
 233     case JFFS2_SUPER_MAGIC:
 234     case NCP_SUPER_MAGIC:
 235     case ROMFS_SUPER_MAGIC:
 236       return 32;
 237
 238     default:
 239       return 32;
 240     }
 241 }
 242
 243
 244 /* Used like: return statfs_link_max (__statfs (name, &buf), &buf); */
 245 long int
 246 __statfs_symlinks (int result, const struct statfs *fsbuf)
 247 {
 248   if (result < 0)
 249     {
 250       if (errno == ENOSYS)
 251         /* Not possible, return the default value.  */
 252         return 1;
 253
 254       /* Some error occurred.  */
 255       return -1;
 256     }
 257
 258   switch (fsbuf->f_type)
 259     {
 260     case ADFS_SUPER_MAGIC:
 261     case BFS_MAGIC:
 262     case CRAMFS_MAGIC:
 263     case DEVPTS_SUPER_MAGIC:
 264     case EFS_SUPER_MAGIC:
 265     case EFS_MAGIC:
 266     case MSDOS_SUPER_MAGIC:
 267     case NTFS_SUPER_MAGIC:
 268     case QNX4_SUPER_MAGIC:
 269     case ROMFS_SUPER_MAGIC:
 270       /* No symlink support.  */
 271       return 0;
 272
 273     default:
 274       return 1;
 275     }
 276 }
 277
 278
 279 /* Used like: return __statfs_chown_restricted (__statfs (name, &buf), &buf);*/
 280 long int
 281 __statfs_chown_restricted (int result, const struct statfs *fsbuf)
 282 {
 283   if (result < 0)
 284     {
 285       if (errno == ENOSYS)
 286         /* Not possible, return the default value.  */
 287         return 1;
 288
 289       /* Some error occurred.  */
 290       return -1;
 291     }
 292
 293   return 1;
 294 }