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Commit d184f6bf authored by Alex Elder's avatar Alex Elder
Browse files

rbd: restore previous rbd id sequence behavior 



It used to be that selecting a new unique identifier for an added
rbd device required searching all existing ones to find the highest
id is used.  A recent change made that unnecessary, but made it
so that id's used were monotonically non-decreasing.  It's a bit
more pleasant to have smaller rbd id's though, and this change
makes ids get allocated as they were before--each new id is one more
than the maximum currently in use.

Signed-off-by: default avatarAlex Elder <elder@dreamhost.com>
Signed-off-by: default avatarSage Weil <sage@newdream.net>
parent 499afd5b

drivers/block/rbd.c

+34 −6
Original line number Diff line number Diff line
@@ -2172,18 +2172,46 @@ static void rbd_id_get(struct rbd_device *rbd_dev) 
 */

static void rbd_id_put(struct rbd_device *rbd_dev)

{

	BUG_ON(rbd_dev->id < 1);

	struct list_head *tmp;

	int rbd_id = rbd_dev->id;

	int max_id;



	BUG_ON(rbd_id < 1);



	spin_lock(&rbd_dev_list_lock);

	list_del_init(&rbd_dev->node);



	/*

	 * If the id being "put" is not the current maximum, there

	 * is nothing special we need to do.

	 */

	if (rbd_id != atomic64_read(&rbd_id_max)) {

		spin_unlock(&rbd_dev_list_lock);

		return;

	}



	/*

	 * We need to update the current maximum id.  Search the

	 * list to find out what it is.  We're more likely to find

	 * the maximum at the end, so search the list backward.

	 */

	max_id = 0;

	list_for_each_prev(tmp, &rbd_dev_list) {

		struct rbd_device *rbd_dev;



		rbd_dev = list_entry(tmp, struct rbd_device, node);

		if (rbd_id > max_id)

			max_id = rbd_id;

	}

	spin_unlock(&rbd_dev_list_lock);



	/*

	 * New id's are always one more than the current maximum.

	 * If the id being "put" *is* that maximum, decrement the

	 * maximum so the next one requested just reuses this one.

	 * The max id could have been updated by rbd_id_get(), in

	 * which case it now accurately reflects the new maximum.

	 * Be careful not to overwrite the maximum value in that

	 * case.

	 */

	atomic64_cmpxchg(&rbd_id_max, rbd_dev->id, rbd_dev->id - 1);

	atomic64_cmpxchg(&rbd_id_max, rbd_id, max_id);

}



static ssize_t rbd_add(struct bus_type *bus,
@@ -2220,7 +2248,7 @@ static ssize_t rbd_add(struct bus_type *bus, 


	init_rwsem(&rbd_dev->header.snap_rwsem);



	/* generate unique id: one more than highest used so far */

	/* generate unique id: find highest unique id, add one */

	rbd_id_get(rbd_dev);



	/* parse add command */