From: Lennart Poettering <email@example.com>
To: Christoph Hellwig <firstname.lastname@example.org>
Cc: Matthew Wilcox <email@example.com>,
Matteo Croce <firstname.lastname@example.org>,
email@example.com, Luca Boccassi <firstname.lastname@example.org>,
Jens Axboe <email@example.com>,
Alexander Viro <firstname.lastname@example.org>,
Damien Le Moal <email@example.com>, Tejun Heo <firstname.lastname@example.org>,
Javier Gonz?lez <email@example.com>,
Niklas Cassel <firstname.lastname@example.org>,
Johannes Thumshirn <email@example.com>,
Hannes Reinecke <firstname.lastname@example.org>
Subject: Re: [PATCH -next 1/5] block: add disk sequence number
Date: Tue, 20 Apr 2021 22:12:15 +0200 [thread overview]
Message-ID: <YH81n34d2G3C4Re+@gardel-login> (raw)
On Di, 16.03.21 14:13, Christoph Hellwig (email@example.com) wrote:
> 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 <firstname.lastname@example.org>
> > >
> > > 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.
I'd argue this makes sense in one way only, i.e. that whenever the
media_change event is seen the seqnum is implicitly bumped.
I am pretty sure though that loopback devices shouldn't synthesize
media_change events themselves though. There's quite a difference I
would argue between a real media change event caused by external
effect (i.e. humans/hw buttons/sensors) to loop device reuse, which is
exclusively triggered by internal events (i.e. local code). Moreover I
think the loopback subsystem should manage the seqnum on its own,
since it ideally would return the assigned seqnum immediately from the
attachment ioctl, i.e. it shouldn't just be a side-effect of
attachment, but a part of it, if you follow what I mean.
Does that make sense?
Matteo, would it make sense to extend your patch set to bump the
seqnum implicitly on media_change for devices that implement that?
next prev parent reply other threads:[~2021-04-20 20:12 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-15 20:02 [PATCH -next 0/5] block: add a sequence number to disks Matteo Croce
2021-03-15 20:02 ` [PATCH -next 1/5] block: add disk sequence number Matteo Croce
2021-03-15 20:18 ` Matthew Wilcox
2021-03-15 21:04 ` Matthew Wilcox
2021-03-15 21:32 ` Lennart Poettering
2021-03-25 17:29 ` Matteo Croce
2021-03-26 8:00 ` Hannes Reinecke
2021-03-25 20:58 ` Lennart Poettering
2021-03-16 14:13 ` Christoph Hellwig
2021-04-20 20:12 ` Lennart Poettering [this message]
2021-03-25 20:52 ` Lennart Poettering
2021-03-16 1:44 ` JeffleXu
2021-03-23 17:43 ` Matteo Croce
2021-03-15 20:02 ` [PATCH -next 2/5] block: add ioctl to read the " Matteo Croce
2021-03-15 20:13 ` Matthew Wilcox
2021-03-15 20:17 ` Damien Le Moal
2021-03-15 20:34 ` Matteo Croce
2021-03-15 20:02 ` [PATCH -next 3/5] block: refactor sysfs code Matteo Croce
2021-03-15 20:02 ` [PATCH -next 4/5] block: export diskseq in sysfs Matteo Croce
2021-03-15 20:02 ` [PATCH -next 5/5] loop: increment sequence number Matteo Croce
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