-------- Original Message --------
Subject: Re: [PATCH 1/2] btrfs: Call mount_subtree() even 'subvolid='
mount option is given.
From: Chandan Rajendra <chandan@xxxxxxxxxxxxxxxxxx>
To: Qu Wenruo <quwenruo@xxxxxxxxxxxxxx>
Date: 2014年07月18日 14:25
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
Oh, I forgot such situation, thanks for the test.
I'll update the patch to V2 to deal the problem.
Thanks,
Qu
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