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

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Message-ID: <20191108171616.GA2569@hermes.olymp>
Date:   Fri, 8 Nov 2019 17:16:16 +0000
From:   Luis Henriques <lhenriques@...e.com>
To:     Sage Weil <sage@...dream.net>
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, Nov 08, 2019 at 04:57:27PM +0000, Sage Weil wrote:
> 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!

Yeah, after sending my reply to Ilya I took a quick look and it _seems_
to be as easy as adding a new encode(require_osd_release...) in the
OSDMap.  And handle the versions, of course.  Let me spend some time
playing with that and I'll try to come up with something during the next
few days.

Thanks for your feedback.

Cheers,
--
Luís