Re: [PATCH 0/2 V3] fix rename: xenstore not fully updated

[Ian Campbell <Ian.Campbell@citrix.com>]

On Fri, 2014-11-21 at 12:01 -0500, Konrad Rzeszutek Wilk wrote:
> On Thu, Nov 20, 2014 at 03:28:30PM +0000, Ian Campbell wrote:
> > On Wed, 2014-11-19 at 16:25 -0500, Konrad Rzeszutek Wilk wrote:
> > > On Wed, Nov 19, 2014 at 11:26:32AM +0000, Ian Jackson wrote:
> > > > Hi Konrad, I have another release ack request:
> > > > 
> > > > Chunyan Liu writes ("[PATCH 0/2 V3] fix rename: xenstore not fully updated"):
> > > > > Currently libxl__domain_rename only update /local/domain/<domid>/name,
> > > > > still some places in xenstore are not updated, including:
> > > > > /vm/<uuid>/name and /local/domain/0/backend/<device>/<domid>/.../domain.
> > > > > This patch series updates /vm/<uuid>/name in xenstore,
> > > > 
> > > > This ("[PATCH 2/2 V3] fix rename: xenstore not fully updated") is a
> > > > bugfix which I think should go into Xen 4.5.
> > > > 
> > > > The risk WITHOUT this patch is that there are out-of-tree tools which
> > > > look here for the domain name and will get confused after it is
> > > > renamed.
> > > 
> > > When was this introduced? Did it exist with Xend?
> > 
> > Based on:
> >  git grep domain\" RELEASE-4.4.0  tools/python/
> >  git grep domain\' RELEASE-4.4.0 tools/python/
> > it doesn't appear so, but someone with a xend install would be needed to
> > confirm for sure.
> > 
> > Given that this has always been wrong for a libxl domain after migration
> > it seems likely to me that noone is looking at this field.
> 
> And this is not a regression though.
> 
> What I am understanding is that we advertise to out-side toolstack
> users for a couple of releases something which is misleading and wrong.

...and also basically useless, there is really no reason to be looking
for the domain's name under a subset of the backend nodes (only vkb, vfb
and console have this key at all). None of the helper function which we
provide do this.

Also these nodes are not advertised as supported either via
docs/misc/xenstore-paths.markdown or xen/include/public/io/*.h.

> My fear is that there such toolstack users out there who will
> get their pitchforks out when this shows up.
> 
> But perhaps there is a way to mitigate this. Is there another way
> (and can it be in the commit description) to get the proper
> domain name? I presume it is just looking at /local/domain/%d/name ?
> 
> As such could this be added:
> 
> "The proper way to get the domain name is to get it from
> /local/domain/%d/name instead from this field."

The proper way is to use libxl_domid_to_name, not to go scrobbling
around in xenstore. We could say this (or both) in the commit message
though if it would help to reassure you.

Either way I think it really would be best to take this fix rather than
worrying overly about the infinitesimal possibility that someone might
be using this key.

Ian.