Re: [PATCH] loop: use BIO list management functions

[Akinobu Mita <akinobu.mita@gmail.com>]

On Fri, Apr 17, 2009 at 08:40:35AM +0200, Jens Axboe wrote:
> On Fri, Apr 17 2009, Akinobu Mita wrote:
> > Impact: cleanup
> 
> This looks good, but please provide a better description than just a
> silly impact notice. I've filled it in for you for this one, but in the
> future the description should say what the patch does.
> 
> It's queued for 2.6.31.

OK, I added the description and Christoph's feedbacks.

Subject: loop: use BIO list management functions

There are BIO list management helpers in bio.h.
This uses them to reduce code duplication in loopback driver.

Cc:  Jens Axboe <axboe@kernel.dk>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
---
 drivers/block/loop.c |   42 +++++++-----------------------------------
 include/linux/bio.h  |    2 +-
 include/linux/loop.h |    3 +--
 3 files changed, 9 insertions(+), 38 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index ddae808..2b70545 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -506,35 +506,6 @@ out:
 	return ret;
 }
 
-/*
- * Add bio to back of pending list
- */
-static void loop_add_bio(struct loop_device *lo, struct bio *bio)
-{
-	if (lo->lo_biotail) {
-		lo->lo_biotail->bi_next = bio;
-		lo->lo_biotail = bio;
-	} else
-		lo->lo_bio = lo->lo_biotail = bio;
-}
-
-/*
- * Grab first pending buffer
- */
-static struct bio *loop_get_bio(struct loop_device *lo)
-{
-	struct bio *bio;
-
-	if ((bio = lo->lo_bio)) {
-		if (bio == lo->lo_biotail)
-			lo->lo_biotail = NULL;
-		lo->lo_bio = bio->bi_next;
-		bio->bi_next = NULL;
-	}
-
-	return bio;
-}
-
 static int loop_make_request(struct request_queue *q, struct bio *old_bio)
 {
 	struct loop_device *lo = q->queuedata;
@@ -550,7 +521,7 @@ static int loop_make_request(struct request_queue *q, struct bio *old_bio)
 		goto out;
 	if (unlikely(rw == WRITE && (lo->lo_flags & LO_FLAGS_READ_ONLY)))
 		goto out;
-	loop_add_bio(lo, old_bio);
+	bio_list_add(&lo->lo_bio_list, old_bio);
 	wake_up(&lo->lo_event);
 	spin_unlock_irq(&lo->lo_lock);
 	return 0;
@@ -609,15 +580,16 @@ static int loop_thread(void *data)
 
 	set_user_nice(current, -20);
 
-	while (!kthread_should_stop() || lo->lo_bio) {
+	while (!kthread_should_stop() || !bio_list_empty(&lo->lo_bio_list)) {
 
 		wait_event_interruptible(lo->lo_event,
-				lo->lo_bio || kthread_should_stop());
+				!bio_list_empty(&lo->lo_bio_list) ||
+				kthread_should_stop());
 
-		if (!lo->lo_bio)
+		if (bio_list_empty(&lo->lo_bio_list))
 			continue;
 		spin_lock_irq(&lo->lo_lock);
-		bio = loop_get_bio(lo);
+		bio = bio_list_pop(&lo->lo_bio_list);
 		spin_unlock_irq(&lo->lo_lock);
 
 		BUG_ON(!bio);
@@ -841,7 +813,7 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
 	lo->old_gfp_mask = mapping_gfp_mask(mapping);
 	mapping_set_gfp_mask(mapping, lo->old_gfp_mask & ~(__GFP_IO|__GFP_FS));
 
-	lo->lo_bio = lo->lo_biotail = NULL;
+	bio_list_init(&lo->lo_bio_list);
 
 	/*
 	 * set queue make_request_fn, and add limits based on lower level
diff --git a/include/linux/bio.h b/include/linux/bio.h
index b89cf2d..9388c55 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -505,7 +505,7 @@ static inline int bio_has_data(struct bio *bio)
 }
 
 /*
- * BIO list managment for use by remapping drivers (e.g. DM or MD).
+ * BIO list management for use by remapping drivers (e.g. DM or MD).
  *
  * A bio_list anchors a singly-linked list of bios chained through the bi_next
  * member of the bio.  The bio_list also caches the last list member to allow
diff --git a/include/linux/loop.h b/include/linux/loop.h
index 4072544..66c194e 100644
--- a/include/linux/loop.h
+++ b/include/linux/loop.h
@@ -56,8 +56,7 @@ struct loop_device {
 	gfp_t		old_gfp_mask;
 
 	spinlock_t		lo_lock;
-	struct bio 		*lo_bio;
-	struct bio		*lo_biotail;
+	struct bio_list		lo_bio_list;
 	int			lo_state;
 	struct mutex		lo_ctl_mutex;
 	struct task_struct	*lo_thread;