Re: [PATCH v5 2/5] libxl: add query function for backend support by device model

[Wei Liu <wei.liu2@citrix.com>]

On Wed, Mar 30, 2016 at 04:55:42PM +0100, Anthony PERARD wrote:
> On Wed, Mar 30, 2016 at 03:26:23PM +0100, Wei Liu wrote:
> > On Wed, Mar 30, 2016 at 04:11:39PM +0200, Juergen Gross wrote:
> > > On 30/03/16 16:09, Wei Liu wrote:
> > > > On Wed, Mar 30, 2016 at 04:02:20PM +0200, Juergen Gross wrote:
> > > >> On 30/03/16 15:53, Wei Liu wrote:
> > > >>> On Wed, Mar 30, 2016 at 02:05:55PM +0200, Juergen Gross wrote:
> > > >>>> Add a function to query whether the device model is supporting a
> > > >>>> specific backend type. The device model is writing the supported
> > > >>>> backend types to Xenstore on startup. The new query function checks
> > > >>>> for the appropriate entry to be present.
> > > >>>>
> > > >>>> As not all versions of qemu are capable to indicate support of
> > > >>>> specific backends the query function is to be called with an indicator
> > > >>>> whether the default return value should be "supported" (in case qemu
> > > >>>> doesn't know set any support information) or "not supported".
> > > >>>>
> > > >>>> Signed-off-by: Juergen Gross <jgross@suse.com>
> > > >>>
> > > >>> The code itself looks straightforward enough.
> > > >>>
> > > >>> But note that this is a new protocol that needs to be supported
> > > >>> essentially forever. I've CC QEMU maintainers for their input.
> > > >>
> > > >> Okay, I'll send the qemu patch now.
> > > >>
> > > > 
> > > > And also a patch to docs/misc/xenstore-paths.markdown please.
> > > 
> > > Aah, sure.
> > > 
> > 
> > Actually wait, I think all QEMU nodes are either under documented or I
> > looked at the wrong place.
> 
> I don't think there is anything missing, in term of PV protocol, which go
> through xenstore. Is there a node in particular that you are thinking of?
> 

The node for video ram? That's what I was looking for. Then I realised
it was probably not documented but I wasn't very sure.

> > Anthony, how should we document the protocol between QEMU and toolstack?
> > Did I look at the wrong place?
> 
> I think xenstore-paths.markdown would be a good place to document this
> protocol.
> 
> -- 
> Anthony PERARD

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