sysdeps/unix/sysv/linux/pathconf.c

   1 /* Get file-specific information about a file.  Linux version.
   2    Copyright (C) 1991-2013 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   int fd;
  43   int flags;
  44
  45   switch (name)
  46     {
  47     case _PC_LINK_MAX:
  48       return __statfs_link_max (__statfs (file, &fsbuf), &fsbuf, file, -1);
  49
  50     case _PC_FILESIZEBITS:
  51       return __statfs_filesize_max (__statfs (file, &fsbuf), &fsbuf);
  52
  53     case _PC_2_SYMLINKS:
  54       return __statfs_symlinks (__statfs (file, &fsbuf), &fsbuf);
  55
  56     case _PC_CHOWN_RESTRICTED:
  57       return __statfs_chown_restricted (__statfs (file, &fsbuf), &fsbuf);
  58
  59     case _PC_PIPE_BUF:
  60       flags = O_RDONLY|O_NONBLOCK|O_NOCTTY;
  61 #ifdef O_CLOEXEC
  62       flags |= O_CLOEXEC;
  63 #endif
  64       fd = open_not_cancel_2 (file, flags);
  65       if (fd >= 0)
  66         {
  67           long int r = __fcntl (fd, F_GETPIPE_SZ);
  68           close_not_cancel_no_status (fd);
  69           if (r > 0)
  70             return r;
  71         }
  72       /* FALLTHROUGH */
  73
  74     default:
  75       return posix_pathconf (file, name);
  76     }
  77 }
  78
  79
  80 static long int
  81 distinguish_extX (const struct statfs *fsbuf, const char *file, int fd)
  82 {
  83   char buf[64];
  84   char path[PATH_MAX];
  85   struct stat64 st;
  86
  87   if ((file == NULL ? fstat64 (fd, &st) : stat64 (file, &st)) != 0)
  88     /* Strange.  The statfd call worked, but stat fails.  Default to
  89        the more pessimistic value.  */
  90     return EXT2_LINK_MAX;
  91
  92   __snprintf (buf, sizeof (buf), "/sys/dev/block/%u:%u",
  93               gnu_dev_major (st.st_dev), gnu_dev_minor (st.st_dev));
  94
  95   ssize_t n = __readlink (buf, path, sizeof (path));
  96   if (n != -1 && n < sizeof (path))
  97     {
  98       path[n] = '\0';
  99       char *base = strdupa (basename (path));
 100       __snprintf (path, sizeof (path), "/sys/fs/ext4/%s", base);
 101
 102       return __access (path, F_OK) == 0 ? EXT4_LINK_MAX : EXT2_LINK_MAX;
 103     }
 104
 105   /* XXX Is there a better way to distinguish ext2/3 from ext4 than
 106      iterating over the mounted filesystems and compare the device
 107      numbers?  */
 108   FILE *mtab = __setmntent ("/proc/mounts", "r");
 109   if (mtab == NULL)
 110     mtab = __setmntent (_PATH_MOUNTED, "r");
 111
 112   /* By default be conservative.  */
 113   long int result = EXT2_LINK_MAX;
 114   if (mtab != NULL)
 115     {
 116       struct mntent mntbuf;
 117       char tmpbuf[1024];
 118
 119       /* No locking needed.  */
 120       (void) __fsetlocking (mtab, FSETLOCKING_BYCALLER);
 121
 122       while (__getmntent_r (mtab, &mntbuf, tmpbuf, sizeof (tmpbuf)))
 123         {
 124           if (strcmp (mntbuf.mnt_type, "ext2") != 0
 125               && strcmp (mntbuf.mnt_type, "ext3") != 0
 126               && strcmp (mntbuf.mnt_type, "ext4") != 0)
 127             continue;
 128
 129           struct stat64 fsst;
 130           if (stat64 (mntbuf.mnt_dir, &fsst) >= 0
 131               && st.st_dev == fsst.st_dev)
 132             {
 133               if (strcmp (mntbuf.mnt_type, "ext4") == 0)
 134                 result = EXT4_LINK_MAX;
 135               break;
 136             }
 137         }
 138
 139       /* Close the file.  */
 140       __endmntent (mtab);
 141     }
 142
 143   return result;
 144 }
 145
 146
 147 /* Used like: return statfs_link_max (__statfs (name, &buf), &buf); */
 148 long int
 149 __statfs_link_max (int result, const struct statfs *fsbuf, const char *file,
 150                    int fd)
 151 {
 152   if (result < 0)
 153     {
 154       if (errno == ENOSYS)
 155         /* Not possible, return the default value.  */
 156         return LINUX_LINK_MAX;
 157
 158       /* Some error occured.  */
 159       return -1;
 160     }
 161
 162   switch (fsbuf->f_type)
 163     {
 164     case EXT2_SUPER_MAGIC:
 165       /* Unfortunately the kernel does not return a different magic number
 166          for ext4.  This would be necessary to easily detect etx4 since it
 167          has a different LINK_MAX value.  Therefore we have to find it out
 168          the hard way.  */
 169       return distinguish_extX (fsbuf, file, fd);
 170
 171     case MINIX_SUPER_MAGIC:
 172     case MINIX_SUPER_MAGIC2:
 173       return MINIX_LINK_MAX;
 174
 175     case MINIX2_SUPER_MAGIC:
 176     case MINIX2_SUPER_MAGIC2:
 177       return MINIX2_LINK_MAX;
 178
 179     case XENIX_SUPER_MAGIC:
 180       return XENIX_LINK_MAX;
 181
 182     case SYSV4_SUPER_MAGIC:
 183     case SYSV2_SUPER_MAGIC:
 184       return SYSV_LINK_MAX;
 185
 186     case COH_SUPER_MAGIC:
 187       return COH_LINK_MAX;
 188
 189     case UFS_MAGIC:
 190     case UFS_CIGAM:
 191       return UFS_LINK_MAX;
 192
 193     case REISERFS_SUPER_MAGIC:
 194       return REISERFS_LINK_MAX;
 195
 196     case XFS_SUPER_MAGIC:
 197       return XFS_LINK_MAX;
 198
 199     case LUSTRE_SUPER_MAGIC:
 200       return LUSTRE_LINK_MAX;
 201
 202     default:
 203       return LINUX_LINK_MAX;
 204     }
 205 }
 206
 207
 208 /* Used like: return statfs_filesize_max (__statfs (name, &buf), &buf); */
 209 long int
 210 __statfs_filesize_max (int result, const struct statfs *fsbuf)
 211 {
 212   if (result < 0)
 213     {
 214       if (errno == ENOSYS)
 215         /* Not possible, return the default value.  */
 216         return 32;
 217
 218       /* Some error occured.  */
 219       return -1;
 220     }
 221
 222   switch (fsbuf->f_type)
 223     {
 224     case BTRFS_SUPER_MAGIC:
 225       return 255;
 226
 227     case EXT2_SUPER_MAGIC:
 228     case UFS_MAGIC:
 229     case UFS_CIGAM:
 230     case REISERFS_SUPER_MAGIC:
 231     case XFS_SUPER_MAGIC:
 232     case SMB_SUPER_MAGIC:
 233     case NTFS_SUPER_MAGIC:
 234     case UDF_SUPER_MAGIC:
 235     case JFS_SUPER_MAGIC:
 236     case VXFS_SUPER_MAGIC:
 237     case CGROUP_SUPER_MAGIC:
 238     case LUSTRE_SUPER_MAGIC:
 239       return 64;
 240
 241     case MSDOS_SUPER_MAGIC:
 242     case JFFS_SUPER_MAGIC:
 243     case JFFS2_SUPER_MAGIC:
 244     case NCP_SUPER_MAGIC:
 245     case ROMFS_SUPER_MAGIC:
 246       return 32;
 247
 248     default:
 249       return 32;
 250     }
 251 }
 252
 253
 254 /* Used like: return statfs_link_max (__statfs (name, &buf), &buf); */
 255 long int
 256 __statfs_symlinks (int result, const struct statfs *fsbuf)
 257 {
 258   if (result < 0)
 259     {
 260       if (errno == ENOSYS)
 261         /* Not possible, return the default value.  */
 262         return 1;
 263
 264       /* Some error occured.  */
 265       return -1;
 266     }
 267
 268   switch (fsbuf->f_type)
 269     {
 270     case ADFS_SUPER_MAGIC:
 271     case BFS_MAGIC:
 272     case CRAMFS_MAGIC:
 273     case DEVPTS_SUPER_MAGIC:
 274     case EFS_SUPER_MAGIC:
 275     case EFS_MAGIC:
 276     case MSDOS_SUPER_MAGIC:
 277     case NTFS_SUPER_MAGIC:
 278     case QNX4_SUPER_MAGIC:
 279     case ROMFS_SUPER_MAGIC:
 280       /* No symlink support.  */
 281       return 0;
 282
 283     default:
 284       return 1;
 285     }
 286 }
 287
 288
 289 /* Used like: return __statfs_chown_restricted (__statfs (name, &buf), &buf);*/
 290 long int
 291 __statfs_chown_restricted (int result, const struct statfs *fsbuf)
 292 {
 293   if (result < 0)
 294     {
 295       if (errno == ENOSYS)
 296         /* Not possible, return the default value.  */
 297         return 1;
 298
 299       /* Some error occured.  */
 300       return -1;
 301     }
 302
 303   int fd;
 304   long int retval = 1;
 305   switch (fsbuf->f_type)
 306     {
 307     case XFS_SUPER_MAGIC:
 308       /* Read the value from /proc/sys/fs/xfs/restrict_chown.  If we cannot
 309          read it default to assume the restriction is in place.  */
 310       fd = open_not_cancel_2 ("/proc/sys/fs/xfs/restrict_chown", O_RDONLY);
 311       if (fd != -1)
 312         {
 313           char buf[2];
 314           if (TEMP_FAILURE_RETRY (read_not_cancel (fd, buf, 2)) == 2
 315               && buf[0] >= '0' && buf[0] <= '1')
 316             retval = buf[0] - '0';
 317
 318           close_not_cancel_no_status (fd);
 319         }
 320       break;
 321
 322     default:
 323       break;
 324     }
 325
 326   return retval;
 327 }