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>
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@ -2172,18 +2172,46 @@ static void rbd_id_get(struct rbd_device *rbd_dev)
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*/
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*/
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static void rbd_id_put(struct rbd_device *rbd_dev)
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static void rbd_id_put(struct rbd_device *rbd_dev)
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{
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{
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BUG_ON(rbd_dev->id < 1);
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struct list_head *tmp;
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int rbd_id = rbd_dev->id;
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int max_id;
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BUG_ON(rbd_id < 1);
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spin_lock(&rbd_dev_list_lock);
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spin_lock(&rbd_dev_list_lock);
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list_del_init(&rbd_dev->node);
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list_del_init(&rbd_dev->node);
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/*
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* If the id being "put" is not the current maximum, there
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* is nothing special we need to do.
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*/
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if (rbd_id != atomic64_read(&rbd_id_max)) {
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spin_unlock(&rbd_dev_list_lock);
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return;
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}
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/*
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* We need to update the current maximum id. Search the
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* list to find out what it is. We're more likely to find
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* the maximum at the end, so search the list backward.
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*/
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max_id = 0;
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list_for_each_prev(tmp, &rbd_dev_list) {
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struct rbd_device *rbd_dev;
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rbd_dev = list_entry(tmp, struct rbd_device, node);
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if (rbd_id > max_id)
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max_id = rbd_id;
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}
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spin_unlock(&rbd_dev_list_lock);
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spin_unlock(&rbd_dev_list_lock);
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/*
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/*
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* New id's are always one more than the current maximum.
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* The max id could have been updated by rbd_id_get(), in
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* If the id being "put" *is* that maximum, decrement the
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* which case it now accurately reflects the new maximum.
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* maximum so the next one requested just reuses this one.
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* Be careful not to overwrite the maximum value in that
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* case.
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*/
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*/
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atomic64_cmpxchg(&rbd_id_max, rbd_dev->id, rbd_dev->id - 1);
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atomic64_cmpxchg(&rbd_id_max, rbd_id, max_id);
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}
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}
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static ssize_t rbd_add(struct bus_type *bus,
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static ssize_t rbd_add(struct bus_type *bus,
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@ -2220,7 +2248,7 @@ static ssize_t rbd_add(struct bus_type *bus,
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init_rwsem(&rbd_dev->header.snap_rwsem);
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init_rwsem(&rbd_dev->header.snap_rwsem);
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/* generate unique id: one more than highest used so far */
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/* generate unique id: find highest unique id, add one */
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rbd_id_get(rbd_dev);
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rbd_id_get(rbd_dev);
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/* parse add command */
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/* parse add command */
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