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SubjectRe: [PATCH -next 1/5] block: add disk sequence number
On Mon, Mar 15, 2021 at 08:18:24PM +0000, Matthew Wilcox wrote:
> On Mon, Mar 15, 2021 at 09:02:38PM +0100, Matteo Croce wrote:
> > From: Matteo Croce <mcroce@microsoft.com>
> >
> > Add a sequence number to the disk devices. This number is put in the
> > uevent so userspace can correlate events when a driver reuses a device,
> > like the loop one.
>
> Should this be documented as monotonically increasing? I think this
> is actually a media identifier. Consider (if you will) a floppy disc.
> Back when such things were common, it was possible with personal computers
> of the era to have multiple floppy discs "in play" and be prompted to
> insert them as needed. So shouldn't it be possible to support something
> similar here -- you're really removing the media from the loop device.
> With a monotonically increasing number, you're always destroying the
> media when you remove it, but in principle, it should be possible to
> reinsert the same media and have the same media identifier number.

And we have some decent infrastructure related to media changes,
grep for disk_events. I think this needs to plug into that
infrastructure instead of duplicating it.

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