jbd2: Add function jbd2_trans_will_send_data_barrier()

Provide a function which returns whether a transaction with given tid
will send a flush to the filesystem device.  The function will be used
by ext4 to detect whether fsync needs to send a separate flush or not.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 41 insertions, 0 deletions

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index cd2d341f602e..9a7826990304 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -588,6 +588,47 @@ int jbd2_journal_start_commit(journal_t *journal, tid_t *ptid)
 }
 
 /*
+ * 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 jbd2_trans_will_send_data_barrier(journal_t *journal, tid_t tid)
+{
+        int ret = 0;
+        transaction_t *commit_trans;
+
+        if (!(journal->j_flags & JBD2_BARRIER))
+                return 0;
+        read_lock(&journal->j_state_lock);
+        /* Transaction already committed? */
+        if (tid_geq(journal->j_commit_sequence, tid))
+                goto out;
+        commit_trans = journal->j_committing_transaction;
+        if (!commit_trans || commit_trans->t_tid != tid) {
+                ret = 1;
+                goto out;
+        }
+        /*
+         * Transaction is being committed and we already proceeded to
+         * submitting a flush to fs partition?
+         */
+        if (journal->j_fs_dev != journal->j_dev) {
+                if (!commit_trans->t_need_data_flush ||
+                    commit_trans->t_state >= T_COMMIT_DFLUSH)
+                        goto out;
+        } else {
+                if (commit_trans->t_state >= T_COMMIT_JFLUSH)
+                        goto out;
+        }
+        ret = 1;
+out:
+        read_unlock(&journal->j_state_lock);
+        return ret;
+}
+EXPORT_SYMBOL(jbd2_trans_will_send_data_barrier);
+
+/*
  * Wait for a specified commit to complete.
  * The caller may not hold the journal lock.
  */