ext4: replace ext4_io_submit->io_op with ->io_wbc

ext4_io_submit_init() takes the pointer to writeback_control to test
its sync_mode and determine between WRITE and WRITE_SYNC and records
the result in ->io_op.  This patch makes it record the pointer
directly and moves the test to ext4_io_submit().

This doesn't cause any noticeable differences now but having
writeback_control available throughout IO submission path will be
depended upon by the planned cgroup writeback support.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NTheodore Ts'o <tytso@mit.edu>

fs/ext4/ext4.h

@@ -187,7 +187,7 @@ typedef struct ext4_io_end {
 } ext4_io_end_t;
 
 struct ext4_io_submit {
-	int			io_op;
+	struct writeback_control *io_wbc;
 	struct bio		*io_bio;
 	ext4_io_end_t		*io_end;
 	sector_t		io_next_block;

fs/ext4/page-io.c

@@ -357,8 +357,10 @@ void ext4_io_submit(struct ext4_io_submit *io)
 	struct bio *bio = io->io_bio;
 
 	if (bio) {
+		int io_op = io->io_wbc->sync_mode == WB_SYNC_ALL ?
+			    WRITE_SYNC : WRITE;
 		bio_get(io->io_bio);
-		submit_bio(io->io_op, io->io_bio);
+		submit_bio(io_op, io->io_bio);
 		bio_put(io->io_bio);
 	}
 	io->io_bio = NULL;
@@ -367,7 +369,7 @@ void ext4_io_submit(struct ext4_io_submit *io)
 void ext4_io_submit_init(struct ext4_io_submit *io,
 			 struct writeback_control *wbc)
 {
-	io->io_op = (wbc->sync_mode == WB_SYNC_ALL ?  WRITE_SYNC : WRITE);
+	io->io_wbc = wbc;
 	io->io_bio = NULL;
 	io->io_end = NULL;
 }