Since there is a filesystem state, we should deal with it carefully at mount,
umount and remount.

- At mount, the FS state should be checked if there is error on these FS.
  If it does have, btrfsck is recommended.
- At umount, the FS state should be saved into disk for consistency.

v2->v3:
do write super stuff at umount time.

Signed-off-by: Liu Bo <liubo2...@cn.fujitsu.com>
---
 fs/btrfs/disk-io.c |   47 ++++++++++++++++++++++++++++++++++++++++++++++-
 1 files changed, 46 insertions(+), 1 deletions(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index b40dfe4..15d795a 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -43,6 +43,8 @@
 static struct extent_io_ops btree_extent_io_ops;
 static void end_workqueue_fn(struct btrfs_work *work);
 static void free_fs_root(struct btrfs_root *root);
+static void btrfs_check_super_valid(struct btrfs_fs_info *fs_info,
+                                   int read_only);
 
 /*
  * end_io_wq structs are used to do processing in task context when an IO is
@@ -1700,6 +1702,11 @@ struct btrfs_root *open_ctree(struct super_block *sb,
        if (!btrfs_super_root(disk_super))
                goto fail_iput;
 
+       /* check filesystem state */
+       fs_info->fs_state |= btrfs_super_flags(disk_super);
+
+       btrfs_check_super_valid(fs_info, sb->s_flags & MS_RDONLY);
+
        ret = btrfs_parse_options(tree_root, options);
        if (ret) {
                err = ret;
@@ -2405,10 +2412,17 @@ int btrfs_commit_super(struct btrfs_root *root)
        up_write(&root->fs_info->cleanup_work_sem);
 
        trans = btrfs_join_transaction(root, 1);
+       if (IS_ERR(trans))
+               return PTR_ERR(trans);
+
        ret = btrfs_commit_transaction(trans, root);
        BUG_ON(ret);
+
        /* run commit again to drop the original snapshot */
        trans = btrfs_join_transaction(root, 1);
+       if (IS_ERR(trans))
+               return PTR_ERR(trans);
+
        btrfs_commit_transaction(trans, root);
        ret = btrfs_write_and_wait_transaction(NULL, root);
        BUG_ON(ret);
@@ -2426,8 +2440,28 @@ int close_ctree(struct btrfs_root *root)
        smp_mb();
 
        btrfs_put_block_group_cache(fs_info);
+
+       /*
+        * Here come 2 situations when btrfs flips readonly:
+        *
+        * 1. when btrfs flips readonly somewhere else before
+        * btrfs_commit_super, sb->s_flags has MS_RDONLY flag,
+        * and btrfs will skip to write sb directly to keep
+        * ERROR state on disk.
+        *
+        * 2. when btrfs flips readonly just in btrfs_commit_super,
+        * and in such case, btrfs cannnot write sb via btrfs_commit_super,
+        * and since fs_state has been set BTRFS_SUPER_FLAG_ERROR flag,
+        * btrfs will directly write sb.
+        */
        if (!(fs_info->sb->s_flags & MS_RDONLY)) {
-               ret =  btrfs_commit_super(root);
+               ret = btrfs_commit_super(root);
+               if (ret)
+                       printk(KERN_ERR "btrfs: commit super ret %d\n", ret);
+       }
+
+       if (fs_info->fs_state & BTRFS_SUPER_FLAG_ERROR) {
+               ret = write_ctree_super(NULL, root, 0);
                if (ret)
                        printk(KERN_ERR "btrfs: commit super ret %d\n", ret);
        }
@@ -2603,6 +2637,17 @@ out:
        return 0;
 }
 
+static void btrfs_check_super_valid(struct btrfs_fs_info *fs_info,
+                             int read_only)
+{
+       if (read_only)
+               return;
+
+       if (fs_info->fs_state & BTRFS_SUPER_FLAG_ERROR)
+               printk(KERN_WARNING "warning: mount fs with errors, "
+                      "running btrfsck is recommended\n");
+}
+
 static struct extent_io_ops btree_extent_io_ops = {
        .write_cache_pages_lock_hook = btree_lock_page_hook,
        .readpage_end_io_hook = btree_readpage_end_io_hook,
-- 
1.7.1
--
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