Btrfs: add flushoncommit mount option

The 'flushoncommit' mount option forces any data dirtied by a write in a
prior transaction to commit as part of the current commit.  This makes
the committed state a fully consistent view of the file system from the
application's perspective (i.e., it includes all completed file system
operations).  This was previously the behavior only when a snapshot is
created.

This is used by Ceph to ensure that completed writes make it to the
platter along with the metadata operations they are bound to (by
BTRFS_IOC_TRANS_{START,END}).

Signed-off-by: Sage Weil <sage@newdream.net>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 3e8225de4e9d..2869b3361eb6 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -972,6 +972,7 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
         int ret;
         int should_grow = 0;
         unsigned long now = get_seconds();
+        int flush_on_commit = btrfs_test_opt(root, FLUSHONCOMMIT);
 
         btrfs_run_ordered_operations(root, 0);
 
@@ -1051,7 +1052,9 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 
                 mutex_unlock(&root->fs_info->trans_mutex);
 
-                if (snap_pending) {
+                if (flush_on_commit || snap_pending) {
+                        if (flush_on_commit)
+                                btrfs_start_delalloc_inodes(root);
                         ret = btrfs_wait_ordered_extents(root, 1);
                         BUG_ON(ret);
                 }