linux-kernel - Re: [RFC PATCH 0/2] ceph: safely use 'copy-from' Op on Octopus OSDs

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Message-ID: <alpine.DEB.2.21.1911081656320.10553@piezo.novalocal>
Date:   Fri, 8 Nov 2019 16:57:27 +0000 (UTC)
From:   Sage Weil <sage@...dream.net>
To:     Luis Henriques <lhenriques@...e.com>
cc:     Ilya Dryomov <idryomov@...il.com>,
        Jeff Layton <jlayton@...nel.org>,
        "Yan, Zheng" <ukernel@...il.com>,
        Ceph Development <ceph-devel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 0/2] ceph: safely use 'copy-from' Op on Octopus
 OSDs

On Fri, 8 Nov 2019, Luis Henriques wrote:
> On Fri, Nov 08, 2019 at 04:15:35PM +0100, Ilya Dryomov wrote:
> > If the OSD checked for unknown flags, like newer syscalls do, it would
> > be super easy, but it looks like it doesn't.
> > 
> > An obvious solution is to look at require_osd_release in osdmap, but we
> > don't decode that in the kernel because it lives the OSD portion of the
> > osdmap.  We could add that and consider the fact that the client now
> > needs to decode more than just the client portion a design mistake.
> > I'm not sure what can of worms does that open and if copy-from alone is
> > worth it though.  Perhaps that field could be moved to (or a copy of it
> > be replicated in) the client portion of the osdmap starting with
> > octopus?  We seem to be running into it on the client side more and
> > more...
> 
> I can't say I'm thrilled with the idea of going back to hack into the
> OSDs code again, I was hoping to be able to handle this with the
> information we already have on the connection peer_features field.  It
> took me *months* to have the OSD fix merged in so I'm not really
> convinced a change to the osdmap would make it into Octopus :-)
> 
> (But I'll have a look at this and see if I can understand what moving or
> replicating the field in the osdmap would really entail.)

Adding a copy of require_osd_release in the client portion of the map is 
an easy thing to do (and probably where it should have gone in the first 
place!).  Let's do that!

sage