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:

quoted

From: Matteo Croce <redacted>

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.