Btrfs-progs: replace find_mount_root from send code

find_mount_root had the problem that it tried to conclude from a file system
path to a mount point, taking the fsid as an indicator. This only works if
no two subvolumes (sharing the same btrfs fsid) are mounted in the same
hierarchy.

Now instead, we're parsing /etc/mtab and look for the longest match.

Signed-off-by: Jan Schmidt <list.btrfs@jan-o-sch.net>

diff --git a/cmds-send.c b/cmds-send.c
index 8a0c110..41ea523 100644 (file)
--- a/cmds-send.c
+++ b/cmds-send.c
@@ -28,6 +28,7 @@
 #include <sys/types.h>
 #include <sys/ioctl.h>
 #include <libgen.h>
+#include <mntent.h>
 
 #include <uuid/uuid.h>
 
@@ -55,82 +56,35 @@ struct btrfs_send {
 
 int find_mount_root(const char *path, char **mount_root)
 {
-       int ret;
-       char *cur;
-       char fsid[BTRFS_FSID_SIZE];
+       FILE *mnttab;
        int fd;
-       struct stat st;
-       char *tmp;
-       char *dup = NULL;
-
-       struct btrfs_ioctl_fs_info_args args;
+       struct mntent *ent;
+       int len;
+       int longest_matchlen = 0;
+       char *longest_match = NULL;
 
        fd = open(path, O_RDONLY | O_NOATIME);
-       if (fd < 0) {
-               ret = -errno;
-               goto out;
-       }
-
-       ret = fstat(fd, &st);
-       if (fd < 0) {
-               ret = -errno;
-               goto out;
-       }
-       if (!S_ISDIR(st.st_mode)) {
-               ret = -ENOTDIR;
-               goto out;
-       }
-
-       ret = ioctl(fd, BTRFS_IOC_FS_INFO, &args);
-       if (fd < 0) {
-               ret = -errno;
-               goto out;
-       }
-       memcpy(fsid, args.fsid, BTRFS_FSID_SIZE);
+       if (fd < 0)
+               return -errno;
        close(fd);
-       fd = -1;
 
-       cur = strdup(path);
-
-       while (1) {
-               dup = strdup(cur);
-               tmp = dirname(dup);
-
-               if (!tmp)
-                       break;
-               fd = open(tmp, O_RDONLY | O_NOATIME);
-               if (fd < 0) {
-                       ret = -errno;
-                       goto out;
+       mnttab = fopen("/etc/mtab", "r");
+       while ((ent = getmntent(mnttab))) {
+               len = strlen(ent->mnt_dir);
+               if (strncmp(ent->mnt_dir, path, len) == 0) {
+                       /* match found */
+                       if (longest_matchlen < len) {
+                               free(longest_match);
+                               longest_matchlen = len;
+                               longest_match = strdup(ent->mnt_dir);
+                       }
                }
-
-               ret = ioctl(fd, BTRFS_IOC_FS_INFO, &args);
-               close(fd);
-               fd = -1;
-               if (ret < 0)
-                       break;
-               if (memcmp(fsid, args.fsid, BTRFS_FSID_SIZE) != 0)
-                       break;
-
-               free(cur);
-               cur = strdup(tmp);
-               free(dup);
-               dup = NULL;
-               if (strcmp(cur, "/") == 0)
-                       break;
-               if (strcmp(cur, ".") == 0)
-                       break;
        }
 
-       ret = 0;
-       *mount_root = realpath(cur, NULL);
+       *mount_root = realpath(longest_match, NULL);
+       free(longest_match);
 
-out:
-       if (dup)
-               free(dup);
-       if (fd != -1)
-               close(fd);
-       return ret;
+       return 0;
 }
 
 static int get_root_id(struct btrfs_send *s, const char *path, u64 *root_id)