[PATCH 25/45] block: simplify bdev/disk lookup in blkdev_get

[Hannes Reinecke]

On 11/28/20 5:14 PM, Christoph Hellwig wrote:
> To simplify block device lookup and a few other upcoming areas, make sure
> that we always have a struct block_device available for each disk and
> each partition, and only find existing block devices in bdget.  The only
> downside of this is that each device and partition uses a little more
> memory.  The upside will be that a lot of code can be simplified.
> 
> With that all we need to look up the block device is to lookup the inode
> and do a few sanity checks on the gendisk, instead of the separate lookup
> for the gendisk.  For blk-cgroup which wants to access a gendisk without
> opening it, a new blkdev_{get,put}_no_open low-level interface is added
> to replace the previous get_gendisk use.
> 
> Note that the change to look up block device directly instead of the two
> step lookup using struct gendisk causes a subtile change in behavior:
> accessing a non-existing partition on an existing block device can now
> cause a call to request_module.  That call is harmless, and in practice
> no recent system will access these nodes as they aren't created by udev
> and static /dev/ setups are unusual.
> 
> Signed-off-by: Christoph Hellwig <hch at lst.de>
> ---
>   block/blk-cgroup.c         |  42 ++++----
>   block/blk-iocost.c         |  36 +++----
>   block/blk.h                |   2 +-
>   block/genhd.c              | 210 +++++--------------------------------
>   block/partitions/core.c    |  29 ++---
>   fs/block_dev.c             | 177 +++++++++++++++++--------------
>   include/linux/blk-cgroup.h |   4 +-
>   include/linux/blkdev.h     |   6 ++
>   include/linux/genhd.h      |   7 +-
>   9 files changed, 194 insertions(+), 319 deletions(-)
> 
Reviewed-by: Hannes Reinecke <hare at suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare at suse.de                              +49 911 74053 688
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