From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Bryn M. Reeves" <bmr@redhat.com>
Subject: Re: dm-statistics: report precise timestamps and
	histogram
Date: Fri, 21 Aug 2015 08:58:08 +0100
Message-ID: <20150821075807.GA30108@bmr.fab.redhat.com>
References: <alpine.LRH.2.02.1508181618100.19666@file01.intranet.prod.int.rdu2.redhat.com>
	<20150818210727.GA17473@redhat.com>
	<alpine.LRH.2.02.1508190650430.7633@file01.intranet.prod.int.rdu2.redhat.com>
	<20150819111122.GE7891@bmr.fab.redhat.com>
	<alpine.LRH.2.02.1508201538560.24681@file01.intranet.prod.int.rdu2.redhat.com>
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To: Mikulas Patocka <mpatocka@redhat.com>
Cc: dm-devel@redhat.com, Bryn Reeves <breeves@redhat.com>, "Alasdair G. Kergon" <agk@redhat.com>, Mike Snitzer <snitzer@redhat.com>
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On Thu, Aug 20, 2015 at 03:40:10PM -0400, Mikulas Patocka wrote:
> 
> 
> On Wed, 19 Aug 2015, Bryn M. Reeves wrote:
> 
> > On Wed, Aug 19, 2015 at 06:53:41AM -0400, Mikulas Patocka wrote:
> > > On Tue, 18 Aug 2015, Mike Snitzer wrote:
> > > > On Tue, Aug 18 2015 at  4:26pm -0400,
> > > > Mikulas Patocka <mpatocka@redhat.com> wrote:
> > > > > Mike, please submit this patch to the upstream kernel before 4.2 is 
> > > > > released, so that the all the kernels that support the options 
> > > > > "precise_timestamps" and "histogram" also report these values back.
> > > > 
> > > > Userspace will have to check the DM ioctl version to know if DM provides
> > > > these extra keywords.
> > > > 
> > > > Mike
> > > 
> > > But if you don't send it, userspace will forever have to deal with kernels 
> > > that don't report this feature back.
> > 
> > We'd either end up saying some kernels can't support it when they can, or
> > have to carry some additional userspace clutter forever to provide a 
> > workaround.
> > 
> > Regards,
> > Bryn.
> 
> I think you don't need to provide a workaround for kernels that don't 
> report it. The workaround would be needed just for 4.2.0 (Mike said he 
> will backport the fix to 4.2.1), there is no need to bloat userspace with 
> that.

That's what's been done; the aux data stuff has been stripped out & I've
set the ioctl version check at 4.33.0.

Bryn.