f2fs: refactor bio->rw handling

This patch introduces f2fs_io_info to mitigate the complex parameter list.

struct f2fs_io_info {
	enum page_type type;		/* contains DATA/NODE/META/META_FLUSH */
	int rw;				/* contains R/RS/W/WS */
	int rw_flag;			/* contains REQ_META/REQ_PRIO */
}

1. f2fs_write_data_pages
 - DATA
 - WRITE_SYNC is set when wbc->WB_SYNC_ALL.

2. sync_node_pages
 - NODE
 - WRITE_SYNC all the time

3. sync_meta_pages
 - META
 - WRITE_SYNC all the time
 - REQ_META | REQ_PRIO all the time

 ** f2fs_submit_merged_bio() handles META_FLUSH.

4. ra_nat_pages, ra_sit_pages, ra_sum_pages
 - META
 - READ_SYNC

Cc: Fan Li <fanofcode.li@samsung.com>
Cc: Changman Lee <cm224.lee@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 68df44a..1674f2f 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -885,8 +885,13 @@
 	spin_lock_init(&sbi->stat_lock);
 
 	mutex_init(&sbi->read_io.io_mutex);
-	for (i = 0; i < NR_PAGE_TYPE; i++)
+	sbi->read_io.sbi = sbi;
+	sbi->read_io.bio = NULL;
+	for (i = 0; i < NR_PAGE_TYPE; i++) {
 		mutex_init(&sbi->write_io[i].io_mutex);
+		sbi->write_io[i].sbi = sbi;
+		sbi->write_io[i].bio = NULL;
+	}
 
 	init_rwsem(&sbi->cp_rwsem);
 	init_waitqueue_head(&sbi->cp_wait);