Re: [Qemu-devel] [PATCH] move 'unsafe' to end of caching modes in help

["Daniel P. Berrange" <berrange@redhat.com>]

On Wed, Jul 21, 2010 at 03:55:28PM -0500, Anthony Liguori wrote:
> On 07/21/2010 03:32 PM, Bruce Rogers wrote:
> >Libvirt parses qemu help output to determine qemu features. In particular
> >  it probes for the following: "cache=writethrough|writeback|none". The
> >  addition of the unsafe cache mode was inserted within this string, as
> >  opposed to being added to the end, which impacted libvirt's probe.
> >  Unbreak libvirt by keeping the existing cache modes intact and add
> >  unsafe to the end.
> >
> >This problem only manifests itself if a caching mode is explicitly
> >specified in the libvirt xml, in which case older syntax for caching is
> >passed to qemu, which it  no longer understands.
> >
> >Signed-off-by: Bruce Rogers<brogers@novell.com>
> >   
> 
> Errr, libvirt is still doing this?
>
> This comes up frequently and it's a real PITA.  Help text is not a 
> feature probing interface.  This is a libvirt bug and it needs to be 
> fixed in libvirt

Of course, there is no viable alternative yet. The QMP patches I
sent a few weeks back now to add ability to query capabilities were
intended to provide the neccessary support in QEMU for us to use
instead of -help. Given that QMP isn't going to be declared stable 
in 0.13 though, it looks like we'll be continuing to use -help 
until the 0.14 release of QEMU.


Regards,
Daniel
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