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Re: [libvirt] [RFC][scale] new API for querying domains stats

----- Original Message -----
> From: "Richard W.M. Jones" <rjones redhat com>
> To: "Li Wei" <lw cn fujitsu com>
> Cc: "Francesco Romani" <fromani redhat com>, libvir-list redhat com
> Sent: Tuesday, August 12, 2014 11:04:05 AM
> Subject: Re: [libvirt] [RFC][scale] new API for querying domains stats

> > > Is it possible to design an API that can work across all domains
> > > in a single call?
> > 
> > How about the following API:
> > 
> > int virConnectGetAllBlockStats(virConnectPtr conn,
> > 				virDomainPtr domain,
> > 				virDomainBlockBulkStatsPtr *stats,
> > 				unsigned int flags);
> > @conn: pointer to libvirt connection
> > @domain: pointer to the domain to be queried, NULL for all domains
> > @stats: array of virDomainBlockBulkStats struct(see below) to be populated
> > @flags: filter flags
> > Return the number of virDomainBlockBulkStats populated.
> > 
> > where virDomainBlockBulkStats defined as:
> > 
> > struct _virDomainBlockBulkStats {
> >     virDomainPtr domain;	 /* domain the block stats belongs to */
> >     virTypedParameterPtr params; /* params to store block stats */
> >     unsigned int nparams;	 /* how many params used for each block stats */
> >     unsigned int ndisks;	 /* how many block stats in this domain */
> > };
> Works for me.

Same here.

oVirt, more specifically VDSM, needs to check all the stats of all
the domains on a given host at once, so this API should fit the task.

Since VDSM takes ownership (read: keep track and control) of all the VMs,
the filtering capability of this new API should be good enough.


It would be nice, but less important, to be able to somehow reuse the 
`stats' argument.

What I'm looking here is a way to avoid to allocate/deallocate every time
all the needed structure before and after each call.

I'm saying so because is a pretty common scenario for a VM (at least in
the cases I'm aware of) to have the same number of disks during all its life.

But I believe this is an optimization which can be added later.


Francesco Romani
RedHat Engineering Virtualization R & D
Phone: 8261328
IRC: fromani

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