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>

fs/btrfs/ctree.h

@@ -1037,6 +1037,7 @@ 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)

fs/btrfs/super.c

@@ -68,7 +68,7 @@ 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 = {
@@ -86,6 +86,7 @@ static match_table_t tokens = {
 	{Opt_ssd, "ssd"},
 	{Opt_noacl, "noacl"},
 	{Opt_notreelog, "notreelog"},
+	{Opt_flushoncommit, "flushoncommit"},
 	{Opt_err, NULL},
 };
 
@@ -229,6 +230,10 @@ 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;
 		}
@@ -370,9 +375,8 @@ static int btrfs_fill_super(struct super_block *sb,
 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;
@@ -419,7 +423,9 @@ static int btrfs_show_options(struct seq_file *seq, struct vfsmount *vfs)
 	if (btrfs_test_opt(root, SSD))
 		seq_puts(seq, ",ssd");
 	if (btrfs_test_opt(root, NOTREELOG))
-		seq_puts(seq, ",notreelog");
+		seq_puts(seq, ",no-treelog");
+	if (btrfs_test_opt(root, FLUSHONCOMMIT))
+		seq_puts(seq, ",flush-on-commit");
 	if (!(root->fs_info->sb->s_flags & MS_POSIXACL))
 		seq_puts(seq, ",noacl");
 	return 0;

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);
 		}