jbd2: split updating of journal superblock and marking journal empty

There are three case of updating journal superblock. In the first case, we want
to mark journal as empty (setting s_sequence to 0), in the second case we want
to update log tail, in the third case we want to update s_errno. Split these
cases into separate functions. It makes the code slightly more straightforward
and later patches will make the distinction even more important.

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

3 files changed, 97 insertions, 70 deletions

diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
index 253e91890e71..19dcd0b86bca 100644
--- a/fs/jbd2/checkpoint.c
+++ b/fs/jbd2/checkpoint.c
@@ -550,7 +550,7 @@ int jbd2_cleanup_journal_tail(journal_t *journal)
             (journal->j_flags & JBD2_BARRIER))
                 blkdev_issue_flush(journal->j_fs_dev, GFP_KERNEL, NULL);
         if (!(journal->j_flags & JBD2_ABORT))
-                jbd2_journal_update_superblock(journal, 1);
+                jbd2_journal_update_sb_log_tail(journal);
         return 0;
 }
 
diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
index 8adc5d460f56..19371a8a9015 100644
--- a/fs/jbd2/commit.c
+++ b/fs/jbd2/commit.c
@@ -340,7 +340,7 @@ void jbd2_journal_commit_transaction(journal_t *journal)
         /* Do we need to erase the effects of a prior jbd2_journal_flush? */
         if (journal->j_flags & JBD2_FLUSHED) {
                 jbd_debug(3, "super block updated\n");
-                jbd2_journal_update_superblock(journal, 1);
+                jbd2_journal_update_sb_log_tail(journal);
         } else {
                 jbd_debug(3, "superblock not updated\n");
         }
diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index cfb36d99f7a4..6e75fbd75bad 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -1110,40 +1110,30 @@ static int journal_reset(journal_t *journal)
 
         journal->j_max_transaction_buffers = journal->j_maxlen / 4;
 
-        /* Add the dynamic fields and write it to disk. */
-        jbd2_journal_update_superblock(journal, 1);
-        return jbd2_journal_start_thread(journal);
-}
-
-/**
- * void jbd2_journal_update_superblock() - Update journal sb on disk.
- * @journal: The journal to update.
- * @wait: Set to '0' if you don't want to wait for IO completion.
- *
- * Update a journal's dynamic superblock fields and write it to disk,
- * optionally waiting for the IO to complete.
- */
-void jbd2_journal_update_superblock(journal_t *journal, int wait)
-{
-        journal_superblock_t *sb = journal->j_superblock;
-        struct buffer_head *bh = journal->j_sb_buffer;
-
         /*
          * As a special case, if the on-disk copy is already marked as needing
-         * no recovery (s_start == 0) and there are no outstanding transactions
-         * in the filesystem, then we can safely defer the superblock update
-         * until the next commit by setting JBD2_FLUSHED.  This avoids
+         * no recovery (s_start == 0), then we can safely defer the superblock
+         * update until the next commit by setting JBD2_FLUSHED.  This avoids
          * attempting a write to a potential-readonly device.
          */
-        if (sb->s_start == 0 && journal->j_tail_sequence ==
-                                journal->j_transaction_sequence) {
+        if (sb->s_start == 0) {
                 jbd_debug(1, "JBD2: Skipping superblock update on recovered sb "
                         "(start %ld, seq %d, errno %d)\n",
                         journal->j_tail, journal->j_tail_sequence,
                         journal->j_errno);
-                goto out;
+                journal->j_flags |= JBD2_FLUSHED;
+        } else {
+                /* Add the dynamic fields and write it to disk. */
+                jbd2_journal_update_sb_log_tail(journal);
         }
+        return jbd2_journal_start_thread(journal);
+}
 
+static void jbd2_write_superblock(journal_t *journal)
+{
+        struct buffer_head *bh = journal->j_sb_buffer;
+
+        trace_jbd2_write_superblock(journal);
         if (buffer_write_io_error(bh)) {
                 /*
                  * Oh, dear.  A previous attempt to write the journal
@@ -1160,49 +1150,98 @@ void jbd2_journal_update_superblock(journal_t *journal, int wait)
                 set_buffer_uptodate(bh);
         }
 
+        BUFFER_TRACE(bh, "marking dirty");
+        mark_buffer_dirty(bh);
+        sync_dirty_buffer(bh);
+        if (buffer_write_io_error(bh)) {
+                printk(KERN_ERR "JBD2: I/O error detected "
+                       "when updating journal superblock for %s.\n",
+                       journal->j_devname);
+                clear_buffer_write_io_error(bh);
+                set_buffer_uptodate(bh);
+        }
+}
+
+/**
+ * jbd2_journal_update_sb_log_tail() - Update log tail in journal sb on disk.
+ * @journal: The journal to update.
+ *
+ * Update a journal's superblock information about log tail and write it to
+ * disk, waiting for the IO to complete.
+ */
+void jbd2_journal_update_sb_log_tail(journal_t *journal)
+{
+        journal_superblock_t *sb = journal->j_superblock;
+
         read_lock(&journal->j_state_lock);
-        jbd_debug(1, "JBD2: updating superblock (start %ld, seq %d, errno %d)\n",
-                  journal->j_tail, journal->j_tail_sequence, journal->j_errno);
+        jbd_debug(1, "JBD2: updating superblock (start %ld, seq %d)\n",
+                  journal->j_tail, journal->j_tail_sequence);
 
         sb->s_sequence = cpu_to_be32(journal->j_tail_sequence);
         sb->s_start    = cpu_to_be32(journal->j_tail);
-        sb->s_errno    = cpu_to_be32(journal->j_errno);
         read_unlock(&journal->j_state_lock);
 
-        BUFFER_TRACE(bh, "marking dirty");
-        mark_buffer_dirty(bh);
-        if (wait) {
-                sync_dirty_buffer(bh);
-                if (buffer_write_io_error(bh)) {
-                        printk(KERN_ERR "JBD2: I/O error detected "
-                               "when updating journal superblock for %s.\n",
-                               journal->j_devname);
-                        clear_buffer_write_io_error(bh);
-                        set_buffer_uptodate(bh);
-                }
-        } else
-                write_dirty_buffer(bh, WRITE);
+        jbd2_write_superblock(journal);
 
-        trace_jbd2_update_superblock_end(journal, wait);
+        /* Log is no longer empty */
+        write_lock(&journal->j_state_lock);
+        WARN_ON(!sb->s_sequence);
+        journal->j_flags &= ~JBD2_FLUSHED;
+        write_unlock(&journal->j_state_lock);
+}
 
-out:
-        /* If we have just flushed the log (by marking s_start==0), then
-         * any future commit will have to be careful to update the
-         * superblock again to re-record the true start of the log. */
+/**
+ * jbd2_mark_journal_empty() - Mark on disk journal as empty.
+ * @journal: The journal to update.
+ *
+ * Update a journal's dynamic superblock fields to show that journal is empty.
+ * Write updated superblock to disk waiting for IO to complete.
+ */
+static void jbd2_mark_journal_empty(journal_t *journal)
+{
+        journal_superblock_t *sb = journal->j_superblock;
+
+        read_lock(&journal->j_state_lock);
+        jbd_debug(1, "JBD2: Marking journal as empty (seq %d)\n",
+                  journal->j_tail_sequence);
+
+        sb->s_sequence = cpu_to_be32(journal->j_tail_sequence);
+        sb->s_start    = cpu_to_be32(0);
+        read_unlock(&journal->j_state_lock);
+
+        jbd2_write_superblock(journal);
 
+        /* Log is no longer empty */
         write_lock(&journal->j_state_lock);
-        if (sb->s_start)
-                journal->j_flags &= ~JBD2_FLUSHED;
-        else
-                journal->j_flags |= JBD2_FLUSHED;
+        journal->j_flags |= JBD2_FLUSHED;
         write_unlock(&journal->j_state_lock);
 }
 
+
+/**
+ * jbd2_journal_update_sb_errno() - Update error in the journal.
+ * @journal: The journal to update.
+ *
+ * Update a journal's errno.  Write updated superblock to disk waiting for IO
+ * to complete.
+ */
+static void jbd2_journal_update_sb_errno(journal_t *journal)
+{
+        journal_superblock_t *sb = journal->j_superblock;
+
+        read_lock(&journal->j_state_lock);
+        jbd_debug(1, "JBD2: updating superblock error (errno %d)\n",
+                  journal->j_errno);
+        sb->s_errno    = cpu_to_be32(journal->j_errno);
+        read_unlock(&journal->j_state_lock);
+
+        jbd2_write_superblock(journal);
+}
+
 /*
  * Read the superblock for a given journal, performing initial
  * validation of the format.
  */
-
 static int journal_get_superblock(journal_t *journal)
 {
         struct buffer_head *bh;
@@ -1395,15 +1434,10 @@ int jbd2_journal_destroy(journal_t *journal)
         spin_unlock(&journal->j_list_lock);
 
         if (journal->j_sb_buffer) {
-                if (!is_journal_aborted(journal)) {
-                        /* We can now mark the journal as empty. */
-                        journal->j_tail = 0;
-                        journal->j_tail_sequence =
-                                ++journal->j_transaction_sequence;
-                        jbd2_journal_update_superblock(journal, 1);
-                } else {
+                if (!is_journal_aborted(journal))
+                        jbd2_mark_journal_empty(journal);
+                else
                         err = -EIO;
-                }
                 brelse(journal->j_sb_buffer);
         }
 
@@ -1562,7 +1596,6 @@ int jbd2_journal_flush(journal_t *journal)
 {
         int err = 0;
         transaction_t *transaction = NULL;
-        unsigned long old_tail;
 
         write_lock(&journal->j_state_lock);
 
@@ -1604,14 +1637,8 @@ int jbd2_journal_flush(journal_t *journal)
          * the magic code for a fully-recovered superblock.  Any future
          * commits of data to the journal will restore the current
          * s_start value. */
+        jbd2_mark_journal_empty(journal);
         write_lock(&journal->j_state_lock);
-        old_tail = journal->j_tail;
-        journal->j_tail = 0;
-        write_unlock(&journal->j_state_lock);
-        jbd2_journal_update_superblock(journal, 1);
-        write_lock(&journal->j_state_lock);
-        journal->j_tail = old_tail;
-
         J_ASSERT(!journal->j_running_transaction);
         J_ASSERT(!journal->j_committing_transaction);
         J_ASSERT(!journal->j_checkpoint_transactions);
@@ -1652,7 +1679,7 @@ int jbd2_journal_wipe(journal_t *journal, int write)
 
         err = jbd2_journal_skip_recovery(journal);
         if (write)
-                jbd2_journal_update_superblock(journal, 1);
+                jbd2_mark_journal_empty(journal);
 
  no_recovery:
         return err;
@@ -1702,7 +1729,7 @@ static void __journal_abort_soft (journal_t *journal, int errno)
         __jbd2_journal_abort_hard(journal);
 
         if (errno)
-                jbd2_journal_update_superblock(journal, 1);
+                jbd2_journal_update_sb_errno(journal);
 }
 
 /**