jbd: Provide function to check whether transaction will issue data barrier

Provide a function which returns whether a transaction with given tid
will send a barrier to the filesystem device. The function will be used
by ext3 to detect whether fsync needs to send a separate barrier or not.

Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 33 insertions, 0 deletions

diff --git a/fs/jbd/journal.c b/fs/jbd/journal.c
index bd224ee..99c71940 100644
--- a/fs/jbd/journal.c
+++ b/fs/jbd/journal.c
@@ -565,6 +565,38 @@ int log_wait_commit(journal_t *journal, tid_t tid)
 }
 
 /*
+ * Return 1 if a given transaction has not yet sent barrier request
+ * connected with a transaction commit. If 0 is returned, transaction
+ * may or may not have sent the barrier. Used to avoid sending barrier
+ * twice in common cases.
+ */
+int journal_trans_will_send_data_barrier(journal_t *journal, tid_t tid)
+{
+	int ret = 0;
+	transaction_t *commit_trans;
+
+	if (!(journal->j_flags & JFS_BARRIER))
+		return 0;
+	spin_lock(&journal->j_state_lock);
+	/* Transaction already committed? */
+	if (tid_geq(journal->j_commit_sequence, tid))
+		goto out;
+	/*
+	 * Transaction is being committed and we already proceeded to
+	 * writing commit record?
+	 */
+	commit_trans = journal->j_committing_transaction;
+	if (commit_trans && commit_trans->t_tid == tid &&
+	    commit_trans->t_state >= T_COMMIT_RECORD)
+		goto out;
+	ret = 1;
+out:
+	spin_unlock(&journal->j_state_lock);
+	return ret;
+}
+EXPORT_SYMBOL(journal_commit_will_send_barrier);
+
+/*
  * Log buffer allocation routines:
  */
 
@@ -1157,6 +1189,7 @@ int journal_destroy(journal_t *journal)
 {
 	int err = 0;
 
+	
 	/* Wait for the commit thread to wake up and die. */
 	journal_kill_thread(journal);