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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 <elder@dreamhost.com>
Signed-off-by: Sage Weil <sage@newdream.net>
This commit is contained in:
Alex Elder 2012-01-29 13:57:44 -06:00
parent 499afd5b8e
commit d184f6bfde
1 changed files with 34 additions and 6 deletions
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40
drivers/block/rbd.c
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@ -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 */