[libvirt] [PATCH v5 1/3] add new virDomainCoreDumpWithFormat API

[Daniel P. Berrange]

On Thu, Mar 13, 2014 at 08:42:40AM +0100, Martin Kletzander wrote:
> On Wed, Mar 12, 2014 at 09:29:55AM -0600, Eric Blake wrote:
> > On 03/12/2014 09:04 AM, Martin Kletzander wrote:
> > > On Thu, Mar 06, 2014 at 09:35:47AM +0000, qiaonuohan at cn.fujitsu.com wrote:
> > >> --memory-only option is introduced without compression supported. Therefore,
> > >> this is a freature regression of virsh dump. Now qemu has support dumping memory
> > >
> > > s/freature/feature/
> > >
> > > but I would not use the word "regression" since that never worked.
> > > Also it would help mentioning the commit ID or a version it
> > > got included in qemu.  On that note, is there a possibility of
> > > of introspection of that feature, so we can gracefully error out in
> > > case older qemu is used?
> >
> > Yes - qemu 2.0 is adding 'query-dump-guest-memory-capability', which can
> > be used for two purposes: 1. if this command exists, 'dump-guest-memory'
> > supports the new optional 'format' argument; and 2. calling this command
> > will return a list of WHICH formats are supported by the given qemu
> > binary (since configure-time choices can disable some of the formats
> > from actually working).  So you need to have a patch that modifies
> > src/qemu/qemu_capabilities.[ch] to do the probing and set capability
> > bits, so that we can gracefully error out when talking to a too-old
> > qemu, or requesting a format that was not compiled in to a new qemu.
> >
> 
> Great.  Could we have the compression parameter just as an arbitrary
> string then (properly checked for, etc.) so there is no need to adapt
> our code to qemu format additions?

I rather prefer it as an enum. Just doing a plain string passthrough
from the API means that the API ends up exposing impl details of
QEMU. This has caused us pain the past - eg nic model XML used to just
be a free-form string, instead of an enum parsed string. The result
was the same NIC model ended up with different names across different
hypervisors. Using an enum / int is good for the API, even if it means
we need to make changes if QEMU adds more formats



Regards,
Daniel
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