From d184f6bfde1428ad4a690d49b28afc9ab4d57b35 Mon Sep 17 00:00:00 2001 From: Alex Elder Date: Sun, 29 Jan 2012 13:57:44 -0600 Subject: [PATCH] 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: Alex Elder Signed-off-by: Sage Weil --- drivers/block/rbd.c | 40 ++++++++++++++++++++++++++++++++++------ 1 file changed, 34 insertions(+), 6 deletions(-) diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c index e7727e8337fc..9ac1484a95ad 100644 --- a/drivers/block/rbd.c +++ b/drivers/block/rbd.c @@ -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 */ -- 2.20.1