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Re: [dm-devel] [PATCH 0/9] Generate uevents for all DM events

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On Wed, Oct 05, 2016 at 01:40:05AM +0100, Alasdair G Kergon wrote:
> 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.

So, no changes need to be made?  I'm confused here, who is wanting this
changed?

greg k-h

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[PATCH 0/9] Generate uevents for all DM events Andy Grover <agrover@redhat.com> - 2016-10-03 21:30 +0200
  [PATCH 4/9] dm: Update dm-uevent.txt Andy Grover <agrover@redhat.com> - 2016-10-03 21:30 +0200
  [PATCH 7/9] dm: Implement dm_uevent_add() Andy Grover <agrover@redhat.com> - 2016-10-03 21:30 +0200
  [PATCH 9/9] dm: Generate uevents for other targets Andy Grover <agrover@redhat.com> - 2016-10-03 21:30 +0200
  [PATCH 3/9] dm: Inline dm_build_path_uevent into dm_path_uevent Andy Grover <agrover@redhat.com> - 2016-10-03 21:30 +0200
  Re: [PATCH 0/9] Generate uevents for all DM events Greg KH <gregkh@linuxfoundation.org> - 2016-10-04 09:50 +0200
    Re: [PATCH 0/9] Generate uevents for all DM events Andy Grover <agrover@redhat.com> - 2016-10-05 01:40 +0200
      Re: [dm-devel] [PATCH 0/9] Generate uevents for all DM events Alasdair G Kergon <agk@redhat.com> - 2016-10-05 02:50 +0200
        Re: [dm-devel] [PATCH 0/9] Generate uevents for all DM events Hannes Reinecke <hare@suse.de> - 2016-10-05 08:30 +0200
        Re: [dm-devel] [PATCH 0/9] Generate uevents for all DM events Greg KH <gregkh@linuxfoundation.org> - 2016-10-05 09:00 +0200
          Re: [dm-devel] [PATCH 0/9] Generate uevents for all DM events Andy Grover <agrover@redhat.com> - 2016-10-05 19:10 +0200
            Re: [dm-devel] [PATCH 0/9] Generate uevents for all DM events Alasdair G Kergon <agk@redhat.com> - 2016-10-05 19:50 +0200
              Re: [dm-devel] [PATCH 0/9] Generate uevents for all DM events Andy Grover <agrover@redhat.com> - 2016-10-06 00:40 +0200

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