Add WRITE_SYNC_PLUG and SWRITE_SYNC_PLUG

(S)WRITE_SYNC always unplugs the device right after IO submission.
Sometimes we want to build up a queue before doing so, so add
variants that explicitly DON'T unplug the queue. The caller must
then do that after submitting all the IO.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/fs.h

@@ -96,7 +96,10 @@ struct inodes_stat_t {
 #define READ_SYNC	(READ | (1 << BIO_RW_SYNCIO) | (1 << BIO_RW_UNPLUG))
 #define READ_META	(READ | (1 << BIO_RW_META))
 #define WRITE_SYNC	(WRITE | (1 << BIO_RW_SYNCIO) | (1 << BIO_RW_UNPLUG))
+#define WRITE_SYNC_PLUG	(WRITE | (1 << BIO_RW_SYNCIO))
 #define SWRITE_SYNC	(SWRITE | (1 << BIO_RW_SYNCIO) | (1 << BIO_RW_UNPLUG))
+#define SWRITE_SYNC_PLUG	\
+	(SWRITE | (1 << BIO_RW_SYNCIO))
 #define WRITE_BARRIER	(WRITE | (1 << BIO_RW_BARRIER))
 #define DISCARD_NOBARRIER (1 << BIO_RW_DISCARD)
 #define DISCARD_BARRIER ((1 << BIO_RW_DISCARD) | (1 << BIO_RW_BARRIER))