Messages in this thread | | | Date | Thu, 19 Jan 2012 10:49:19 -0500 | From | Vivek Goyal <> | Subject | Re: [PATCH 12/12] blkcg: kill the mind-bending blkg->dev |
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On Wed, Jan 18, 2012 at 05:11:30PM -0800, Tejun Heo wrote: > blkg->dev is dev_t recording the device number of the block device for > the associated request_queue. It is used to identify the associated > block device when printing out configuration or stats. > > This is redundant to begin with. A blkg is an association between a > cgroup and a request_queue and it of course is possible to reach > request_queue from blkg and synchronization conventions are in place > for safe q dereferencing, so this shouldn't be necessary from the > beginning. Furthermore, it's initialized by sscanf()ing the device > name of backing_dev_info. The mind boggles. > > Anyways, if blkg is visible under rcu lock, we *know* that the > associated request_queue hasn't gone away yet and its bdi is > registered and alive - blkg can't be created for request_queue which > hasn't been fully initialized and it can't go away before blkg is > removed. > > Let stat and conf read functions get device name from > blkg->q->backing_dev_info.dev and pass it down to printing functions > and remove blkg->dev.
I think one of the reasons for not using blkg->q->backing_dev_info.dev was that there were still drivers where multiple gendisks were sharing the request queue.
Thanks Vivek
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