From: Alasdair G Kergon <agk@redhat.com>
To: Andy Grover <agrover@redhat.com>
Cc: Greg KH <gregkh@linuxfoundation.org>,
dm-devel@redhat.com, linux-kernel@vger.kernel.org,
snitzer@redhat.com
Subject: Re: [dm-devel] [PATCH 0/9] Generate uevents for all DM events
Date: Wed, 5 Oct 2016 01:40:05 +0100 [thread overview]
Message-ID: <20161005004004.GC28416@agk-dp.fab.redhat.com> (raw)
In-Reply-To: <fe185eba-f802-6731-8da7-736c117db135@redhat.com>
On Tue, Oct 04, 2016 at 04:39:28PM -0700, Andy Grover wrote:
> devicemapper is using uevents for:
> a. dm-verity detected corruption
> b. dm-multipath: path failed or reinstated
> c. dm device renamed
> d. there's also some use in md and bcache.
>
> devicemapper uses DM_EVENT ioctl (yuck) for:
> 1. dm-thin pool data/metadata filling up (hit a threshold)
> 2. dm-cache is now clean
> 3. dm-log flushed or log failed
> 4. dm-raid error detected or sync complete
> there doesn't seem to be much technical differentiation between the
> two lists.
The distinction in dm is that events in the first category may affect
the availability of the device: they represent major (and hopefully
rare) changes.
Events in the second category are just notifications: no impact on /dev,
no need to trigger udev rules, and their use will continue to be
extended, and (rarely at the moment) could be frequent (which is no
problem for the existing polling-based mechanism).
> Instead of using uevent for everything, we could go to a separate
> genetlink for 1-4 instead of making them use uevent like a-d, but we'd
> end up with two different userspace notification techniques.
We see these as two different categories of notifications, and prefer
the greater flexibility a mechanism independent of uevents would
provide. The team has discussed several alternatives over the years but
didn't make a decision as we've not yet reached a point where we're
straining the existing mechanism too far.
Alasdair
next prev parent reply other threads:[~2016-10-05 0:40 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-03 19:22 [PATCH 0/9] Generate uevents for all DM events Andy Grover
2016-10-03 19:22 ` [PATCH 1/9] dm: Do not export dm_send_uevents Andy Grover
2016-10-03 19:22 ` [PATCH 2/9] dm: Move multipath-specific stuff out of dm-uevent.c Andy Grover
2016-10-03 19:22 ` [PATCH 3/9] dm: Inline dm_build_path_uevent into dm_path_uevent Andy Grover
2016-10-03 19:22 ` [PATCH 4/9] dm: Update dm-uevent.txt Andy Grover
2016-10-03 19:22 ` [PATCH 5/9] dm: Rename dm_build_uevent to dm_uevent_build Andy Grover
2016-10-03 19:22 ` [PATCH 6/9] dm: Rename dm_event_add to dm_event_queue Andy Grover
2016-10-03 19:22 ` [PATCH 7/9] dm: Implement dm_uevent_add() Andy Grover
2016-10-03 19:22 ` [PATCH 8/9] dm: Generate uevents for thin targets Andy Grover
2016-10-03 19:23 ` [PATCH 9/9] dm: Generate uevents for other targets Andy Grover
2016-10-03 19:29 ` [PATCH 0/9] Generate uevents for all DM events Mike Snitzer
2016-10-04 7:20 ` Greg KH
2016-10-04 23:39 ` Andy Grover
2016-10-05 0:40 ` Alasdair G Kergon [this message]
2016-10-05 6:26 ` [dm-devel] " Hannes Reinecke
2016-10-05 6:51 ` Greg KH
2016-10-05 17:06 ` Andy Grover
2016-10-05 17:43 ` Alasdair G Kergon
2016-10-05 22:30 ` Andy Grover
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20161005004004.GC28416@agk-dp.fab.redhat.com \
--to=agk@redhat.com \
--cc=agrover@redhat.com \
--cc=dm-devel@redhat.com \
--cc=gregkh@linuxfoundation.org \
--cc=linux-kernel@vger.kernel.org \
--cc=snitzer@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).