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, 10 insertions, 4 deletions

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 3baa2c109e55..9744af9d71e9 100644
--- a/fs/btrfs/super.c
+++ b/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 @@ 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;
@@ -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;