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Btrfs: prevent loops in the directory tree when creating snapshots

Browse Source 
For a directory tree:

/mnt/subvolA/subvolB

btrfsctl -s /mnt/subvolA/subvolB /mnt

Will create a directory loop with subvolA under subvolB.  This
commit uses the forward refs for each subvol and snapshot to error out
before creating the loop.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
This commit is contained in:
Chris Mason 2008-11-17 21:14:24 -05:00
parent 0660b5af3f
commit ea9e8b11bd
4 changed files with 73 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
fs/btrfs/ctree.h
View File

@ -1801,6 +1801,9 @@ int btrfs_drop_subtree(struct btrfs_trans_handle *trans,
struct extent_buffer *node,
struct extent_buffer *parent);
/* root-item.c */
int btrfs_find_root_ref(struct btrfs_root *tree_root,
struct btrfs_path *path,
u64 root_id, u64 ref_id);
int btrfs_add_root_ref(struct btrfs_trans_handle *trans,
struct btrfs_root *tree_root,
u64 root_id, u8 type, u64 ref_id,

5
fs/btrfs/disk-io.c
View File

@ -1129,7 +1129,7 @@ struct btrfs_root *btrfs_read_fs_root(struct btrfs_fs_info *fs_info,
kfree(root);
return ERR_PTR(ret);
}
#if 0
ret = btrfs_sysfs_add_root(root);
if (ret) {
free_extent_buffer(root->node);
@ -1137,6 +1137,7 @@ struct btrfs_root *btrfs_read_fs_root(struct btrfs_fs_info *fs_info,
kfree(root);
return ERR_PTR(ret);
}
#endif
root->in_sysfs = 1;
return root;
}
@ -1963,8 +1964,10 @@ int btrfs_free_fs_root(struct btrfs_fs_info *fs_info, struct btrfs_root *root)
down_write(&root->anon_super.s_umount);
kill_anon_super(&root->anon_super);
}
#if 0
if (root->in_sysfs)
btrfs_sysfs_del_root(root);
#endif
if (root->node)
free_extent_buffer(root->node);
if (root->commit_root)

50
fs/btrfs/ioctl.c
View File

@ -284,6 +284,56 @@ static noinline int btrfs_mksubvol(struct path *parent, char *name,
* subvolume with specific mode bits.
*/
if (snap_src) {
struct dentry *dir = dentry->d_parent;
struct dentry *test = dir->d_parent;
struct btrfs_path *path = btrfs_alloc_path();
int ret;
u64 test_oid;
u64 parent_oid = BTRFS_I(dir->d_inode)->root->root_key.objectid;
test_oid = snap_src->root_key.objectid;
ret = btrfs_find_root_ref(snap_src->fs_info->tree_root,
path, parent_oid, test_oid);
if (ret == 0)
goto create;
btrfs_release_path(snap_src->fs_info->tree_root, path);
/* we need to make sure we aren't creating a directory loop
* by taking a snapshot of something that has our current
* subvol in its directory tree. So, this loops through
* the dentries and checks the forward refs for each subvolume
* to see if is references the subvolume where we are
* placing this new snapshot.
*/
while(1) {
if (!test ||
dir == snap_src->fs_info->sb->s_root ||
test == snap_src->fs_info->sb->s_root ||
test->d_inode->i_sb != snap_src->fs_info->sb) {
break;
}
if (S_ISLNK(test->d_inode->i_mode)) {
printk("Symlink in snapshot path, failed\n");
error = -EMLINK;
btrfs_free_path(path);
goto out_drop_write;
}
test_oid =
BTRFS_I(test->d_inode)->root->root_key.objectid;
ret = btrfs_find_root_ref(snap_src->fs_info->tree_root,
path, test_oid, parent_oid);
if (ret == 0) {
printk("Snapshot creation failed, looping\n");
error = -EMLINK;
btrfs_free_path(path);
goto out_drop_write;
}
btrfs_release_path(snap_src->fs_info->tree_root, path);
test = test->d_parent;
}
create:
btrfs_free_path(path);
error = create_snapshot(snap_src, dentry, name, namelen);
} else {
error = create_subvol(BTRFS_I(parent->dentry->d_inode)->root,

16
fs/btrfs/root-tree.c
View File

@ -300,6 +300,22 @@ int btrfs_del_root_ref(struct btrfs_trans_handle *trans,
return ret;
}
int btrfs_find_root_ref(struct btrfs_root *tree_root,
struct btrfs_path *path,
u64 root_id, u64 ref_id)
{
struct btrfs_key key;
int ret;
key.objectid = root_id;
key.type = BTRFS_ROOT_REF_KEY;
key.offset = ref_id;
ret = btrfs_search_slot(NULL, tree_root, &key, path, 0, 0);
return ret;
}
/*
* add a btrfs_root_ref item. type is either BTRFS_ROOT_REF_KEY
* or BTRFS_ROOT_BACKREF_KEY.