Commit ba40a2aa authored by Alasdair G Kergon's avatar Alasdair G Kergon Committed by Linus Torvalds
Browse files

[PATCH] dm snapshot: tidy snapshot_map 



This patch rearranges the snapshot_map code so that the functional changes in
subsequent patches are clearer.

The only functional change is to replace the existing read lock with a write
lock which the next patch needs.

Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 927ffe7c

drivers/md/dm-snap.c

+26 −46
Original line number Diff line number Diff line
@@ -851,7 +851,6 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio, 
{

	struct exception *e;

	struct dm_snapshot *s = (struct dm_snapshot *) ti->private;

	int copy_needed = 0;

	int r = 1;

	chunk_t chunk;

	struct pending_exception *pe = NULL;
@@ -866,13 +865,6 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio, 
	if (unlikely(bio_barrier(bio)))

		return -EOPNOTSUPP;



	/*

	 * Write to snapshot - higher level takes care of RW/RO

	 * flags so we should only get this if we are

	 * writeable.

	 */

	if (bio_rw(bio) == WRITE) {



	/* FIXME: should only take write lock if we need

	 * to copy an exception */

	down_write(&s->lock);
@@ -889,6 +881,12 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio, 
		goto out_unlock;

	}



	/*

	 * Write to snapshot - higher level takes care of RW/RO

	 * flags so we should only get this if we are

	 * writeable.

	 */

	if (bio_rw(bio) == WRITE) {

		pe = __find_pending_exception(s, bio);

		if (!pe) {

			__invalidate_snapshot(s, pe, -ENOMEM);
@@ -899,45 +897,27 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio, 
		remap_exception(s, &pe->e, bio);

		bio_list_add(&pe->snapshot_bios, bio);



		r = 0;



		if (!pe->started) {

			/* this is protected by snap->lock */

			pe->started = 1;

			copy_needed = 1;

		}



		r = 0;



 out_unlock:

			up_write(&s->lock);



		if (copy_needed)

			start_copy(pe);

	} else {

			goto out;

		}

	} else

		/*

		 * FIXME: this read path scares me because we

		 * always use the origin when we have a pending

		 * exception.  However I can't think of a

		 * situation where this is wrong - ejt.

		 */



		/* Do reads */

		down_read(&s->lock);



		if (!s->valid) {

			up_read(&s->lock);

			return -EIO;

		}



		/* See if it it has been remapped */

		e = lookup_exception(&s->complete, chunk);

		if (e)

			remap_exception(s, e, bio);

		else

		bio->bi_bdev = s->origin->bdev;



		up_read(&s->lock);

	}



 out_unlock:

	up_write(&s->lock);

 out:

	return r;

}