[PATCH] exfat: do not clear VolumeDirty in writeback

[Yuezhang.Mo@xxxxxxxx]

Before this commit, VolumeDirty will be cleared first in
writeback if 'dirsync' or 'sync' is not enabled. If the power
is suddenly cut off after cleaning VolumeDirty but other
updates are not written, the exFAT filesystem will not be able
to detect the power failure in the next mount.

And VolumeDirty will be set again when updating the parent
directory. It means that BootSector will be written twice in each
writeback, that will shorten the life of the device.

Reviewed-by: Andy.Wu <Andy.Wu@xxxxxxxx>
Reviewed-by: Aoyama, Wataru <wataru.aoyama@xxxxxxxx>
Signed-off-by: Yuezhang.Mo <Yuezhang.Mo@xxxxxxxx>
---
 fs/exfat/super.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/fs/exfat/super.c b/fs/exfat/super.c
index 8c9fb7dcec16..f4906c17475e 100644
--- a/fs/exfat/super.c
+++ b/fs/exfat/super.c
@@ -25,6 +25,8 @@
 static char exfat_default_iocharset[] = CONFIG_EXFAT_DEFAULT_IOCHARSET;
 static struct kmem_cache *exfat_inode_cachep;
 
+static int __exfat_clear_volume_dirty(struct super_block *sb);
+
 static void exfat_free_iocharset(struct exfat_sb_info *sbi)
 {
 	if (sbi->options.iocharset != exfat_default_iocharset)
@@ -64,7 +66,7 @@ static int exfat_sync_fs(struct super_block *sb, int wait)
 	/* If there are some dirty buffers in the bdev inode */
 	mutex_lock(&sbi->s_lock);
 	sync_blockdev(sb->s_bdev);
-	if (exfat_clear_volume_dirty(sb))
+	if (__exfat_clear_volume_dirty(sb))
 		err = -EIO;
 	mutex_unlock(&sbi->s_lock);
 	return err;
@@ -139,13 +141,21 @@ int exfat_set_volume_dirty(struct super_block *sb)
 	return exfat_set_vol_flags(sb, sbi->vol_flags | VOLUME_DIRTY);
 }
 
-int exfat_clear_volume_dirty(struct super_block *sb)
+static int __exfat_clear_volume_dirty(struct super_block *sb)
 {
 	struct exfat_sb_info *sbi = EXFAT_SB(sb);
 
 	return exfat_set_vol_flags(sb, sbi->vol_flags & ~VOLUME_DIRTY);
 }
 
+int exfat_clear_volume_dirty(struct super_block *sb)
+{
+	if (sb->s_flags & (SB_SYNCHRONOUS | SB_DIRSYNC))
+		return __exfat_clear_volume_dirty(sb);
+
+	return 0;
+}
+
 static int exfat_show_options(struct seq_file *m, struct dentry *root)
 {
 	struct super_block *sb = root->d_sb;
-- 
2.25.1