Btrfs: check UUID tree during mount if required

If the filesystem was mounted with an old kernel that was not
aware of the UUID tree, this is detected by looking at the
uuid_tree_generation field of the superblock (similar to how
the free space cache is doing it). If a mismatch is detected
at mount time, a thread is started that does two things:
1. Iterate through the UUID tree, check each entry, delete those
   entries that are not valid anymore (i.e., the subvol does not
   exist anymore or the value changed).
2. Iterate through the root tree, for each found subvolume, add
   the UUID tree entries for the subvolume (if they are not
   already there).

This mechanism is also used to handle and repair errors that
happened during the initial creation and filling of the tree.
The update of the uuid_tree_generation field (which indicates
that the state of the UUID tree is up to date) is blocked until
all create and repair operations are successfully completed.

Signed-off-by: Stefan Behrens <sbehrens@giantdisaster.de>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

1 files changed, 83 insertions, 0 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 4066803fe765..75bdea6bf188 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -3559,10 +3559,76 @@ out:
         btrfs_free_path(path);
         if (ret)
                 pr_warn("btrfs: btrfs_uuid_scan_kthread failed %d\n", ret);
+        else
+                fs_info->update_uuid_tree_gen = 1;
         up(&fs_info->uuid_tree_rescan_sem);
         return 0;
 }
 
+/*
+ * Callback for btrfs_uuid_tree_iterate().
+ * returns:
+ * 0    check succeeded, the entry is not outdated.
+ * < 0  if an error occured.
+ * > 0  if the check failed, which means the caller shall remove the entry.
+ */
+static int btrfs_check_uuid_tree_entry(struct btrfs_fs_info *fs_info,
+                                       u8 *uuid, u8 type, u64 subid)
+{
+        struct btrfs_key key;
+        int ret = 0;
+        struct btrfs_root *subvol_root;
+
+        if (type != BTRFS_UUID_KEY_SUBVOL &&
+            type != BTRFS_UUID_KEY_RECEIVED_SUBVOL)
+                goto out;
+
+        key.objectid = subid;
+        key.type = BTRFS_ROOT_ITEM_KEY;
+        key.offset = (u64)-1;
+        subvol_root = btrfs_read_fs_root_no_name(fs_info, &key);
+        if (IS_ERR(subvol_root)) {
+                ret = PTR_ERR(subvol_root);
+                if (ret == -ENOENT)
+                        ret = 1;
+                goto out;
+        }
+
+        switch (type) {
+        case BTRFS_UUID_KEY_SUBVOL:
+                if (memcmp(uuid, subvol_root->root_item.uuid, BTRFS_UUID_SIZE))
+                        ret = 1;
+                break;
+        case BTRFS_UUID_KEY_RECEIVED_SUBVOL:
+                if (memcmp(uuid, subvol_root->root_item.received_uuid,
+                           BTRFS_UUID_SIZE))
+                        ret = 1;
+                break;
+        }
+
+out:
+        return ret;
+}
+
+static int btrfs_uuid_rescan_kthread(void *data)
+{
+        struct btrfs_fs_info *fs_info = (struct btrfs_fs_info *)data;
+        int ret;
+
+        /*
+         * 1st step is to iterate through the existing UUID tree and
+         * to delete all entries that contain outdated data.
+         * 2nd step is to add all missing entries to the UUID tree.
+         */
+        ret = btrfs_uuid_tree_iterate(fs_info, btrfs_check_uuid_tree_entry);
+        if (ret < 0) {
+                pr_warn("btrfs: iterating uuid_tree failed %d\n", ret);
+                up(&fs_info->uuid_tree_rescan_sem);
+                return ret;
+        }
+        return btrfs_uuid_scan_kthread(data);
+}
+
 int btrfs_create_uuid_tree(struct btrfs_fs_info *fs_info)
 {
         struct btrfs_trans_handle *trans;
@@ -3596,6 +3662,7 @@ int btrfs_create_uuid_tree(struct btrfs_fs_info *fs_info)
         down(&fs_info->uuid_tree_rescan_sem);
         task = kthread_run(btrfs_uuid_scan_kthread, fs_info, "btrfs-uuid");
         if (IS_ERR(task)) {
+                /* fs_info->update_uuid_tree_gen remains 0 in all error case */
                 pr_warn("btrfs: failed to start uuid_scan task\n");
                 up(&fs_info->uuid_tree_rescan_sem);
                 return PTR_ERR(task);
@@ -3604,6 +3671,22 @@ int btrfs_create_uuid_tree(struct btrfs_fs_info *fs_info)
         return 0;
 }
 
+int btrfs_check_uuid_tree(struct btrfs_fs_info *fs_info)
+{
+        struct task_struct *task;
+
+        down(&fs_info->uuid_tree_rescan_sem);
+        task = kthread_run(btrfs_uuid_rescan_kthread, fs_info, "btrfs-uuid");
+        if (IS_ERR(task)) {
+                /* fs_info->update_uuid_tree_gen remains 0 in all error case */
+                pr_warn("btrfs: failed to start uuid_rescan task\n");
+                up(&fs_info->uuid_tree_rescan_sem);
+                return PTR_ERR(task);
+        }
+
+        return 0;
+}
+
 /*
  * shrinking a device means finding all of the device extents past
  * the new size, and then following the back refs to the chunks.