mnt_usable.c

   1 /*
   2  * Copyright (C) 2012-2020 all contributors <cmogstored-public@yhbt.net>
   3  * License: GPL-3.0+ <https://www.gnu.org/licenses/gpl-3.0.txt>
   4  */
   5 #include "cmogstored.h"
   6
   7 /*
   8  * statvfs() on GNU/Linux may call stat() internally, and stat() is bad
   9  * for network mounts which may be stalled/slow, so favor the non-portable
  10  * statfs() on GNU/Linux
  11  */
  12 #ifdef __linux__
  13 #include <sys/vfs.h>
  14 #define MY_STATFS statfs
  15 #else /* statvfs() is POSIX */
  16 #define MY_STATFS statvfs
  17 #endif
  18
  19 static bool resolve_symlink(char **orig)
  20 {
  21         char *p = canonicalize_filename_mode(*orig, CAN_EXISTING);
  22
  23         if (p) {
  24                 free(*orig);
  25                 *orig = p;
  26                 return true;
  27         }
  28         return false;
  29 }
  30
  31 static bool stat_harder(struct mount_entry *me)
  32 {
  33         struct stat sb;
  34
  35         /* the device number may not have been populated, do it */
  36         if (me->me_dev == (dev_t)-1) {
  37                 if (stat(me->me_mountdir, &sb) != 0)
  38                         return false;
  39                 me->me_dev = sb.st_dev;
  40         }
  41
  42         /*
  43          * resolve symlinks for things that look like paths
  44          * and skip dead symlinks
  45          */
  46         if (me->me_devname[0] == '/') {
  47                 if (lstat(me->me_devname, &sb) == 0
  48                     && S_ISLNK(sb.st_mode)
  49                     && ! resolve_symlink(&me->me_devname))
  50                         return false;
  51         }
  52         return true;
  53 }
  54
  55 /*
  56  * prevents us from using filesystems of unknown size, since those could
  57  * be stalled/dead network mounts
  58  */
  59 bool mog_mnt_usable(struct mount_entry *me)
  60 {
  61         struct MY_STATFS buf;
  62         const char *path = me->me_mountdir;
  63
  64         if (me->me_dummy)
  65                 return false;
  66
  67 retry:
  68         errno = 0;
  69         if (MY_STATFS(path, &buf) == 0)
  70                 return (buf.f_blocks > 0) ? stat_harder(me) : false;
  71
  72         /* unknown */
  73         assert(errno != EFAULT && "BUG: EFAULT from statfs/statvfs");
  74         switch (errno) {
  75         case EINTR: goto retry;
  76         case EIO: /* this is important enough to log: */
  77         case EOVERFLOW: /* this is important enough to log: */
  78                 syslog(LOG_ERR, MOG_STR(MY_STATFS) "(%s) failed: %m", path);
  79         case ENOTDIR: /* race between read_file_system_list and statvfs */
  80         case ELOOP: /* race between read_file_system_list and statvfs? */
  81         case ENOSYS: /* if statvfs() doesn't work, fstatvfs() won't, either */
  82         case EACCES: /* this is common */
  83                 return false;
  84         }
  85         /*
  86          * assume other errors are recoverable (or fail elsewhere)
  87          * ENAMETOOLONG - would fail anyways if we need to stat(2)
  88          * ENOMEM - maybe the kernel will get more memory back, soon
  89          */
  90         return true;
  91 }