From: Matthew Wilcox <willy@infradead.org>
To: Matteo Croce <mcroce@linux.microsoft.com>
Cc: linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org,
"Lennart Poettering" <lennart@poettering.net>,
"Luca Boccassi" <bluca@debian.org>,
"Jens Axboe" <axboe@kernel.dk>,
"Alexander Viro" <viro@zeniv.linux.org.uk>,
"Damien Le Moal" <damien.lemoal@wdc.com>,
"Tejun Heo" <tj@kernel.org>,
"Javier González" <javier@javigon.com>,
"Niklas Cassel" <niklas.cassel@wdc.com>,
"Johannes Thumshirn" <johannes.thumshirn@wdc.com>,
"Hannes Reinecke" <hare@suse.de>
Subject: Re: [PATCH -next 1/5] block: add disk sequence number
Date: Mon, 15 Mar 2021 21:04:52 +0000 [thread overview]
Message-ID: <20210315210452.GC2577561@casper.infradead.org> (raw)
In-Reply-To: <20210315201824.GB2577561@casper.infradead.org>
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.
So ... a lot of devices have UUIDs or similar. eg:
$ cat /sys/block/nvme0n1/uuid
e8238fa6-bf53-0001-001b-448b49cec94f
https://linux.die.net/man/8/scsi_id (for scsi)
how about making this way more generic; create an xattr on a file to
store the uuid (if one doesn't already exist) whenever it's used as the
base for a loop device. then sysfs (or whatever) can report the contents
of that xattr as the unique id.
That can be mostly in userspace -- losetup can create it, and read it.
It can be passed in as the first two current-reserved __u64 entries in
loop_config. The only kernel change should be creating the sysfs
entry /sys/block/loopN/uuid from those two array entries.
next prev parent reply other threads:[~2021-03-15 21:06 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 [this message]
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
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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