[RFC PATCH v2 2/5] jbd2: introduce journal callbacks j_submit|finish_inode_data_buffers

[Mauricio Faria de Oliveira <mfo@canonical.com>]

Add the callbacks as opt-in to override the default behavior for
the transaction's inode list, instead of moving that code around.

This is important as not only ext4 uses the inode list: ocfs2 too,
via jbd2_journal_inode_ranged_write(), and maybe out-of-tree code.

To opt-out of the default behavior (i.e., to do nothing), one has
to opt-in with a no-op function.
---
 fs/jbd2/commit.c     | 21 ++++++++++++++++-----
 include/linux/jbd2.h | 21 ++++++++++++++++++++-
 2 files changed, 36 insertions(+), 6 deletions(-)

diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
index 51f713089e35..b98d227b50d8 100644
--- a/fs/jbd2/commit.c
+++ b/fs/jbd2/commit.c
@@ -237,10 +237,14 @@ static int journal_submit_data_buffers(journal_t *journal,
 		 * instead of writepages. Because writepages can do
 		 * block allocation  with delalloc. We need to write
 		 * only allocated blocks here.
+		 * This can be overriden with a custom callback.
 		 */
 		trace_jbd2_submit_inode_data(jinode->i_vfs_inode);
-		err = journal_submit_inode_data_buffers(mapping, dirty_start,
-				dirty_end);
+		if (journal->j_submit_inode_data_buffers)
+			err = journal->j_submit_inode_data_buffers(jinode);
+		else
+			err = journal_submit_inode_data_buffers(mapping,
+					dirty_start, dirty_end);
 		if (!ret)
 			ret = err;
 		spin_lock(&journal->j_list_lock);
@@ -274,9 +278,16 @@ static int journal_finish_inode_data_buffers(journal_t *journal,
 			continue;
 		jinode->i_flags |= JI_COMMIT_RUNNING;
 		spin_unlock(&journal->j_list_lock);
-		err = filemap_fdatawait_range_keep_errors(
-				jinode->i_vfs_inode->i_mapping, dirty_start,
-				dirty_end);
+		/*
+		 * Wait for the inode data buffers writeout.
+		 * This can be overriden with a custom callback.
+		 */
+		if (journal->j_finish_inode_data_buffers)
+			err = journal->j_finish_inode_data_buffers(jinode);
+		else
+			err = filemap_fdatawait_range_keep_errors(
+					jinode->i_vfs_inode->i_mapping,
+					dirty_start, dirty_end);
 		if (!ret)
 			ret = err;
 		spin_lock(&journal->j_list_lock);
diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index d56128df2aff..24efe88eda1b 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -628,7 +628,8 @@ struct transaction_s
 	struct journal_head	*t_shadow_list;
 
 	/*
-	 * List of inodes whose data we've modified in data=ordered mode.
+	 * List of inodes whose data we've modified in data=ordered mode
+	 * or whose pages we should write-protect in data=journaled mode.
 	 * [j_list_lock]
 	 */
 	struct list_head	t_inode_list;
@@ -1110,6 +1111,24 @@ struct journal_s
 	void			(*j_commit_callback)(journal_t *,
 						     transaction_t *);
 
+	/**
+	 * @j_submit_inode_data_buffers:
+	 *
+	 * This function is called before flushing metadata buffers.
+	 * This overrides the default behavior (writeout data buffers.)
+	 */
+	int			(*j_submit_inode_data_buffers)
+					(struct jbd2_inode *);
+
+	/**
+	 * @j_finish_inode_data_buffers:
+	 *
+	 * This function is called after flushing metadata buffers.
+	 * This overrides the default behavior (wait writeout.)
+	 */
+	int			(*j_finish_inode_data_buffers)
+					(struct jbd2_inode *);
+
 	/*
 	 * Journal statistics
 	 */
-- 
2.17.1