ext4: Support for checksumming from journal triggers

JBD2 layer support triggers which are called when journaling layer moves
buffer to a certain state. We can use the frozen trigger, which gets
called when buffer data is frozen and about to be written out to the
journal, to compute block checksums for some buffer types (similarly as
does ocfs2). This avoids unnecessary repeated recomputation of the
checksum (at the cost of larger window where memory corruption won't be
caught by checksumming) and is even necessary when there are
unsynchronized updaters of the checksummed data.

So add superblock and journal trigger type arguments to
ext4_journal_get_write_access() and ext4_journal_get_create_access() so
that frozen triggers can be set accordingly. Also add inode argument to
ext4_walk_page_buffers() and all the callbacks used with that function
for the same purpose. This patch is mostly only a change of prototype of
the above mentioned functions and a few small helpers. Real checksumming
will come later.

Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20210816095713.16537-1-jack@suse.cz
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

1 files changed, 15 insertions, 1 deletions

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 970013c93d3e..9d4e13ef5f56 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -4014,6 +4014,20 @@ static const char *ext4_quota_mode(struct super_block *sb)
 #endif
 }
 
+static void ext4_setup_csum_trigger(struct super_block *sb,
+				    enum ext4_journal_trigger_type type,
+				    void (*trigger)(
+					struct jbd2_buffer_trigger_type *type,
+					struct buffer_head *bh,
+					void *mapped_data,
+					size_t size))
+{
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
+
+	sbi->s_journal_triggers[type].sb = sb;
+	sbi->s_journal_triggers[type].tr_triggers.t_frozen = trigger;
+}
+
 static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 {
 	struct dax_device *dax_dev = fs_dax_get_by_bdev(sb->s_bdev);
@@ -6617,7 +6631,7 @@ static ssize_t ext4_quota_write(struct super_block *sb, int type,
 	if (!bh)
 		goto out;
 	BUFFER_TRACE(bh, "get write access");
-	err = ext4_journal_get_write_access(handle, bh);
+	err = ext4_journal_get_write_access(handle, sb, bh, EXT4_JTR_NONE);
 	if (err) {
 		brelse(bh);
 		return err;