[PATCH 2/3] ext4: support freezing ext2 (nojournal) file systems

[Theodore Ts'o <tytso@mit.edu>]

Through an oversight, when we added nojournal support to ext4, we
didn't add support to allow file system freezing.  This is relatively
easy to add, so let's do it.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reported-by: Dexuan Cui <decui@microsoft.com>
---
 fs/ext4/super.c | 27 ++++++++++++++++-----------
 1 file changed, 16 insertions(+), 11 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 4770c98..921d5b4 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1131,6 +1131,8 @@ static const struct super_operations ext4_nojournal_sops = {
 	.drop_inode	= ext4_drop_inode,
 	.evict_inode	= ext4_evict_inode,
 	.sync_fs	= ext4_sync_fs,
+	.freeze_fs	= ext4_freeze,
+	.unfreeze_fs	= ext4_unfreeze,
 	.put_super	= ext4_put_super,
 	.statfs		= ext4_statfs,
 	.remount_fs	= ext4_remount,
@@ -4758,23 +4760,26 @@ static int ext4_freeze(struct super_block *sb)
 
 	journal = EXT4_SB(sb)->s_journal;
 
-	/* Now we set up the journal barrier. */
-	jbd2_journal_lock_updates(journal);
+	if (journal) {
+		/* Now we set up the journal barrier. */
+		jbd2_journal_lock_updates(journal);
 
-	/*
-	 * Don't clear the needs_recovery flag if we failed to flush
-	 * the journal.
-	 */
-	error = jbd2_journal_flush(journal);
-	if (error < 0)
-		goto out;
+		/*
+		 * Don't clear the needs_recovery flag if we failed to
+		 * flush the journal.
+		 */
+		error = jbd2_journal_flush(journal);
+		if (error < 0)
+			goto out;
+	}
 
 	/* Journal blocked and flushed, clear needs_recovery flag. */
 	EXT4_CLEAR_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_RECOVER);
 	error = ext4_commit_super(sb, 1);
 out:
-	/* we rely on upper layer to stop further updates */
-	jbd2_journal_unlock_updates(EXT4_SB(sb)->s_journal);
+	if (journal)
+		/* we rely on upper layer to stop further updates */
+		jbd2_journal_unlock_updates(EXT4_SB(sb)->s_journal);
 	return error;
 }
 
-- 
2.1.0