btrfs: scrub

This adds an initial implementation for scrub. It works quite
straightforward. The usermode issues an ioctl for each device in the
fs. For each device, it enumerates the allocated device chunks. For
each chunk, the contained extents are enumerated and the data checksums
fetched. The extents are read sequentially and the checksums verified.
If an error occurs (checksum or EIO), a good copy is searched for. If
one is found, the bad copy will be rewritten.
All enumerations happen from the commit roots. During a transaction
commit, the scrubs get paused and afterwards continue from the new
roots.

This commit is based on the series originally posted to linux-btrfs
with some improvements that resulted from comments from David Sterba,
Ilya Dryomov and Jan Schmidt.

Signed-off-by: Arne Jansen <sensille@gmx.net>

1 files changed, 3 insertions, 0 deletions

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index c571734d5e5a..37c2302a08d4 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -1321,6 +1321,7 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 
         WARN_ON(cur_trans != trans->transaction);
 
+        btrfs_scrub_pause(root);
         /* btrfs_commit_tree_roots is responsible for getting the
          * various roots consistent with each other.  Every pointer
          * in the tree of tree roots has to point to the most up to date
@@ -1405,6 +1406,8 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 
         mutex_unlock(&root->fs_info->trans_mutex);
 
+        btrfs_scrub_continue(root);
+
         if (current->journal_info == trans)
                 current->journal_info = NULL;