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>

3 files changed, 15 insertions, 5 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 1e99a9948637..bb6ac5b87652 100644
--- a/fs/btrfs/ctree.h
+++ b/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)
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;
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);
                 }