[PATCH 24/45] blk-cgroup: stop abusing get_gendisk

[Tejun Heo]

On Tue, Nov 24, 2020 at 02:27:30PM +0100, Christoph Hellwig wrote:
> Properly open the device instead of relying on deep internals by
> using get_gendisk.  Note that this uses FMODE_NDELAY without either
> FMODE_READ or FMODE_WRITE, which is a special open mode to allow
> for opening without media access, thus avoiding unexpexted interactions
> especially on removable media.

I'm not sure FMODE_NDELAY does that. e.g. sd_open() does media change check
and full revalidation including disk spin up regadless of NDELAY and it's
odd and can lead to nasty surprises to require cgroup configuration updates
to wait for SCSI EH.

Thanks.

-- 
tejun