sysdeps/unix/sysv/linux/pathconf.c

   1 /* Get file-specific information about a file.  Linux version.
   2    Copyright (C) 1991-2014 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    <http://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 st;
  69
  70   if ((file == NULL ? fstat64 (fd, &st) : stat64 (file, &st)) != 0)
  71     /* Strange.  The statfd call worked, but stat fails.  Default to
  72        the more pessimistic value.  */
  73     return EXT2_LINK_MAX;
  74
  75   __snprintf (buf, sizeof (buf), "/sys/dev/block/%u:%u",
  76               gnu_dev_major (st.st_dev), gnu_dev_minor (st.st_dev));
  77
  78   ssize_t n = __readlink (buf, path, sizeof (path));
  79   if (n != -1 && n < sizeof (path))
  80     {
  81       path[n] = '\0';
  82       char *base = strdupa (basename (path));
  83       __snprintf (path, sizeof (path), "/sys/fs/ext4/%s", base);
  84
  85       return __access (path, F_OK) == 0 ? EXT4_LINK_MAX : EXT2_LINK_MAX;
  86     }
  87
  88   /* XXX Is there a better way to distinguish ext2/3 from ext4 than
  89      iterating over the mounted filesystems and compare the device
  90      numbers?  */
  91   FILE *mtab = __setmntent ("/proc/mounts", "r");
  92   if (mtab == NULL)
  93     mtab = __setmntent (_PATH_MOUNTED, "r");
  94
  95   /* By default be conservative.  */
  96   long int result = EXT2_LINK_MAX;
  97   if (mtab != NULL)
  98     {
  99       struct mntent mntbuf;
 100       char tmpbuf[1024];
 101
 102       /* No locking needed.  */
 103       (void) __fsetlocking (mtab, FSETLOCKING_BYCALLER);
 104
 105       while (__getmntent_r (mtab, &mntbuf, tmpbuf, sizeof (tmpbuf)))
 106         {
 107           if (strcmp (mntbuf.mnt_type, "ext2") != 0
 108               && strcmp (mntbuf.mnt_type, "ext3") != 0
 109               && strcmp (mntbuf.mnt_type, "ext4") != 0)
 110             continue;
 111
 112           struct stat64 fsst;
 113           if (stat64 (mntbuf.mnt_dir, &fsst) >= 0
 114               && st.st_dev == fsst.st_dev)
 115             {
 116               if (strcmp (mntbuf.mnt_type, "ext4") == 0)
 117                 result = EXT4_LINK_MAX;
 118               break;
 119             }
 120         }
 121
 122       /* Close the file.  */
 123       __endmntent (mtab);
 124     }
 125
 126   return result;
 127 }
 128
 129
 130 /* Used like: return statfs_link_max (__statfs (name, &buf), &buf); */
 131 long int
 132 __statfs_link_max (int result, const struct statfs *fsbuf, const char *file,
 133                    int fd)
 134 {
 135   if (result < 0)
 136     {
 137       if (errno == ENOSYS)
 138         /* Not possible, return the default value.  */
 139         return LINUX_LINK_MAX;
 140
 141       /* Some error occured.  */
 142       return -1;
 143     }
 144
 145   switch (fsbuf->f_type)
 146     {
 147     case EXT2_SUPER_MAGIC:
 148       /* Unfortunately the kernel does not return a different magic number
 149          for ext4.  This would be necessary to easily detect etx4 since it
 150          has a different LINK_MAX value.  Therefore we have to find it out
 151          the hard way.  */
 152       return distinguish_extX (fsbuf, file, fd);
 153
 154     case F2FS_SUPER_MAGIC:
 155       return F2FS_LINK_MAX;
 156
 157     case MINIX_SUPER_MAGIC:
 158     case MINIX_SUPER_MAGIC2:
 159       return MINIX_LINK_MAX;
 160
 161     case MINIX2_SUPER_MAGIC:
 162     case MINIX2_SUPER_MAGIC2:
 163       return MINIX2_LINK_MAX;
 164
 165     case XENIX_SUPER_MAGIC:
 166       return XENIX_LINK_MAX;
 167
 168     case SYSV4_SUPER_MAGIC:
 169     case SYSV2_SUPER_MAGIC:
 170       return SYSV_LINK_MAX;
 171
 172     case COH_SUPER_MAGIC:
 173       return COH_LINK_MAX;
 174
 175     case UFS_MAGIC:
 176     case UFS_CIGAM:
 177       return UFS_LINK_MAX;
 178
 179     case REISERFS_SUPER_MAGIC:
 180       return REISERFS_LINK_MAX;
 181
 182     case XFS_SUPER_MAGIC:
 183       return XFS_LINK_MAX;
 184
 185     case LUSTRE_SUPER_MAGIC:
 186       return LUSTRE_LINK_MAX;
 187
 188     default:
 189       return LINUX_LINK_MAX;
 190     }
 191 }
 192
 193
 194 /* Used like: return statfs_filesize_max (__statfs (name, &buf), &buf); */
 195 long int
 196 __statfs_filesize_max (int result, const struct statfs *fsbuf)
 197 {
 198   if (result < 0)
 199     {
 200       if (errno == ENOSYS)
 201         /* Not possible, return the default value.  */
 202         return 32;
 203
 204       /* Some error occured.  */
 205       return -1;
 206     }
 207
 208   switch (fsbuf->f_type)
 209     {
 210     case F2FS_SUPER_MAGIC:
 211       return 256;
 212
 213     case BTRFS_SUPER_MAGIC:
 214       return 255;
 215
 216     case EXT2_SUPER_MAGIC:
 217     case UFS_MAGIC:
 218     case UFS_CIGAM:
 219     case REISERFS_SUPER_MAGIC:
 220     case XFS_SUPER_MAGIC:
 221     case SMB_SUPER_MAGIC:
 222     case NTFS_SUPER_MAGIC:
 223     case UDF_SUPER_MAGIC:
 224     case JFS_SUPER_MAGIC:
 225     case VXFS_SUPER_MAGIC:
 226     case CGROUP_SUPER_MAGIC:
 227     case LUSTRE_SUPER_MAGIC:
 228       return 64;
 229
 230     case MSDOS_SUPER_MAGIC:
 231     case JFFS_SUPER_MAGIC:
 232     case JFFS2_SUPER_MAGIC:
 233     case NCP_SUPER_MAGIC:
 234     case ROMFS_SUPER_MAGIC:
 235       return 32;
 236
 237     default:
 238       return 32;
 239     }
 240 }
 241
 242
 243 /* Used like: return statfs_link_max (__statfs (name, &buf), &buf); */
 244 long int
 245 __statfs_symlinks (int result, const struct statfs *fsbuf)
 246 {
 247   if (result < 0)
 248     {
 249       if (errno == ENOSYS)
 250         /* Not possible, return the default value.  */
 251         return 1;
 252
 253       /* Some error occured.  */
 254       return -1;
 255     }
 256
 257   switch (fsbuf->f_type)
 258     {
 259     case ADFS_SUPER_MAGIC:
 260     case BFS_MAGIC:
 261     case CRAMFS_MAGIC:
 262     case DEVPTS_SUPER_MAGIC:
 263     case EFS_SUPER_MAGIC:
 264     case EFS_MAGIC:
 265     case MSDOS_SUPER_MAGIC:
 266     case NTFS_SUPER_MAGIC:
 267     case QNX4_SUPER_MAGIC:
 268     case ROMFS_SUPER_MAGIC:
 269       /* No symlink support.  */
 270       return 0;
 271
 272     default:
 273       return 1;
 274     }
 275 }
 276
 277
 278 /* Used like: return __statfs_chown_restricted (__statfs (name, &buf), &buf);*/
 279 long int
 280 __statfs_chown_restricted (int result, const struct statfs *fsbuf)
 281 {
 282   if (result < 0)
 283     {
 284       if (errno == ENOSYS)
 285         /* Not possible, return the default value.  */
 286         return 1;
 287
 288       /* Some error occured.  */
 289       return -1;
 290     }
 291
 292 #if __ASSUME_XFS_RESTRICTED_CHOWN
 293   return 1;
 294 #else
 295   int fd;
 296   int save_errno;
 297   long int retval = 1;
 298   switch (fsbuf->f_type)
 299     {
 300     case XFS_SUPER_MAGIC:
 301       save_errno = errno;
 302       /* Read the value from /proc/sys/fs/xfs/restrict_chown.  If we cannot
 303          read it default to assume the restriction is in place.  */
 304       fd = open_not_cancel_2 ("/proc/sys/fs/xfs/restrict_chown", O_RDONLY);
 305       if (fd != -1)
 306         {
 307           char buf[2];
 308           if (TEMP_FAILURE_RETRY (read_not_cancel (fd, buf, 2)) == 2
 309               && buf[0] >= '0' && buf[0] <= '1')
 310             retval = buf[0] - '0';
 311
 312           close_not_cancel_no_status (fd);
 313         }
 314       __set_errno (save_errno);
 315       break;
 316
 317     default:
 318       break;
 319     }
 320
 321   return retval;
 322 #endif
 323 }