[PATCH] btrfs: flushoncommit mount option

[Sage Weil <sage@newdream.net>]

Hi Chris-

Here's a simpler version of the patch that drops the unrelated sync_fs 
stuff.

thanks-
sage


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>
---
 fs/btrfs/ctree.h       |    1 +
 fs/btrfs/super.c       |   10 +++++++---
 fs/btrfs/transaction.c |    5 ++++-
 3 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 471fa67..019e7a7 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -951,6 +951,7 @@ struct btrfs_root {
 #define BTRFS_MOUNT_DEGRADED		(1 << 4)
 #define BTRFS_MOUNT_COMPRESS		(1 << 5)
 #define BTRFS_MOUNT_NOTREELOG           (1 << 6)
+#define BTRFS_MOUNT_FLUSHONCOMMIT       (1 << 7)
 
 #define btrfs_clear_opt(o, opt)		((o) &= ~BTRFS_MOUNT_##opt)
 #define btrfs_set_opt(o, opt)		((o) |= BTRFS_MOUNT_##opt)
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index d8c664c..2b33a6a 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -67,7 +67,7 @@ enum {
 	Opt_degraded, Opt_subvol, Opt_device, Opt_nodatasum, Opt_nodatacow,
 	Opt_max_extent, Opt_max_inline, Opt_alloc_start, Opt_nobarrier,
 	Opt_ssd, Opt_thread_pool, Opt_noacl,  Opt_compress, Opt_notreelog,
-	Opt_err,
+	Opt_flushoncommit, Opt_err,
 };
 
 static match_table_t tokens = {
@@ -85,6 +85,7 @@ static match_table_t tokens = {
 	{Opt_ssd, "ssd"},
 	{Opt_noacl, "noacl"},
 	{Opt_notreelog, "notreelog"},
+	{Opt_flushoncommit, "flushoncommit"},
 	{Opt_err, NULL},
 };
 
@@ -228,6 +229,10 @@ int btrfs_parse_options(struct btrfs_root *root, char *options)
 			printk(KERN_INFO "btrfs: disabling tree log\n");
 			btrfs_set_opt(info->mount_opt, NOTREELOG);
 			break;
+		case Opt_flushoncommit:
+			printk(KERN_INFO "btrfs: turning on flush-on-commit\n");
+			btrfs_set_opt(info->mount_opt, FLUSHONCOMMIT);
+			break;
 		default:
 			break;
 		}
@@ -369,9 +374,8 @@ fail_close:
 int btrfs_sync_fs(struct super_block *sb, int wait)
 {
 	struct btrfs_trans_handle *trans;
-	struct btrfs_root *root;
+	struct btrfs_root *root = btrfs_sb(sb);
 	int ret;
-	root = btrfs_sb(sb);
 
 	if (sb->s_flags & MS_RDONLY)
 		return 0;
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 919172d..b8822d5 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -892,6 +892,7 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 	struct extent_io_tree *pinned_copy;
 	DEFINE_WAIT(wait);
 	int ret;
+	int ordered = btrfs_test_opt(root, FLUSHONCOMMIT);
 
 	INIT_LIST_HEAD(&dirty_fs_roots);
 	mutex_lock(&root->fs_info->trans_mutex);
@@ -952,7 +953,9 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 
 		mutex_unlock(&root->fs_info->trans_mutex);
 
-		if (snap_pending) {
+		if (ordered || snap_pending) {
+			if (ordered)
+				btrfs_start_delalloc_inodes(root);
 			ret = btrfs_wait_ordered_extents(root, 1);
 			BUG_ON(ret);
 		}
-- 
1.5.6.5