On Wednesday 16 Jul 2014 12:07:10 Qu Wenruo wrote:
> +/* Find the path for given subvol_objectid.
> + * Caller needs to readlock the root tree and kzalloc PATH_MAX for
> + * subvol_name and namebuf */
> +static char *find_subvol_by_id(struct btrfs_root *root, u64 subvol_objectid)
> +{
> + struct btrfs_key key;
> + struct btrfs_key found_key;
> + struct btrfs_root_ref *ref;
> + struct btrfs_path *path;
> + char *namebuf = NULL;
> + char *new_buf = NULL;
> + char *subvol_ret = NULL;
> + int ret = 0;
> + u16 namelen = 0;
> +
> + path = btrfs_alloc_path();
> + /* Alloc 1 byte for later strlen() calls */
> + subvol_ret = kzalloc(1, GFP_NOFS);
> + if (!path || !subvol_ret) {
> + ret = -ENOMEM;
> + goto out;
> + }
> +
> + key.objectid = subvol_objectid;
> + key.type = BTRFS_ROOT_BACKREF_KEY;
> + key.offset = 0;
> + /* We don't need to lock the tree_root,
> + * if when we do the backref walking, some one deleted/moved
> + * the subvol, we just return -ENOENT or let mount_subtree
> + * return -ENOENT and no disaster will happen.
> + * User should not modify subvolume when trying to mount it */
> + while (key.objectid != BTRFS_FS_TREE_OBJECTID) {
> + ret = btrfs_search_slot_for_read(root, &key, path, 1, 1);
> + if (ret < 0)
> + goto out;
> + if (ret) {
> + ret = -ENOENT;
> + goto out;
> + }
> + btrfs_item_key_to_cpu(path->nodes[0], &found_key,
> + path->slots[0]);
> + if (found_key.objectid != key.objectid ||
> + found_key.type != BTRFS_ROOT_BACKREF_KEY) {
> + ret = -ENOENT;
> + goto out;
> + }
> + key.objectid = found_key.offset;
> + ref = btrfs_item_ptr(path->nodes[0], path->slots[0],
> + struct btrfs_root_ref);
> + namelen = btrfs_root_ref_name_len(path->nodes[0], ref);
> + /* One for ending '\0' One for '/' */
> + new_buf = krealloc(namebuf, namelen + 2, GFP_NOFS);
> + if (!new_buf) {
> + ret = -ENOMEM;
> + goto out;
> + }
> + namebuf = new_buf;
> + read_extent_buffer(path->nodes[0], namebuf,
> + (unsigned long)(ref + 1), namelen);
> + btrfs_release_path(path);
> + *(namebuf + namelen) = '/';
> + *(namebuf + namelen + 1) = '\0';
> +
> + new_buf = krealloc(subvol_ret, strlen(subvol_ret) + namelen + 2,
> + GFP_NOFS);
> + if (!new_buf) {
> + ret = -ENOMEM;
> + goto out;
> + }
> + subvol_ret = new_buf;
> + str_append_head(subvol_ret, namebuf);
> + }
> +out:
> + kfree(namebuf);
> + btrfs_free_path(path);
> + if (ret < 0) {
> + kfree(subvol_ret);
> + return ERR_PTR(ret);
> + } else
> + return subvol_ret;
> +
> +}
Hello Qu Wenruo,
If the subvolume being mounted exists in a sub-directory of the parent's
subvolume, then the find_subvol_by_id() fails to contruct the correct
path to the subvolume. Hence mount would fail.
For e.g.
[root@guest0 ~]# btrfs subvolume list /mnt/btrfs/
ID 257 gen 7 top level 5 path dir1/sub1
[root@guest0 ~]# umount /mnt/btrfs
[root@guest0 ~]# mount -o subvolid=257 /dev/loop0 /mnt/btrfs/
mount: mount(2) failed: No such file or directory
--
chandan
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