Re: [Qemu-devel] [PATCH v3 8/9] qmp: add query-block-jobs

[Luiz Capitulino <lcapitulino@redhat.com>]

On Thu, 15 Dec 2011 12:00:16 +0000
Stefan Hajnoczi <stefanha@gmail.com> wrote:

> On Thu, Dec 15, 2011 at 11:30 AM, Luiz Capitulino
> <lcapitulino@redhat.com> wrote:
> > On Thu, 15 Dec 2011 11:34:07 +0100
> > Kevin Wolf <kwolf@redhat.com> wrote:
> >
> >> Am 15.12.2011 09:27, schrieb Stefan Hajnoczi:
> >> > On Wed, Dec 14, 2011 at 03:54:52PM +0100, Kevin Wolf wrote:
> >> >> Am 13.12.2011 14:52, schrieb Stefan Hajnoczi:
> >> >>> diff --git a/hmp.c b/hmp.c
> >> >>> index 66d9d0f..c16d6a1 100644
> >> >>> --- a/hmp.c
> >> >>> +++ b/hmp.c
> >> >>> @@ -499,6 +499,46 @@ void hmp_info_pci(Monitor *mon)
> >> >>>      qapi_free_PciInfoList(info);
> >> >>>  }
> >> >>>
> >> >>> +void hmp_info_block_jobs(Monitor *mon)
> >> >>> +{
> >> >>> +    BlockJobInfoList *list;
> >> >>> +    Error *err = NULL;
> >> >>> +
> >> >>> +    list = qmp_query_block_jobs(&err);
> >> >>> +    assert(!err);
> >> >>> +
> >> >>> +    if (!list) {
> >> >>> +        monitor_printf(mon, "No active jobs\n");
> >> >>> +        return;
> >> >>> +    }
> >> >>> +
> >> >>> +    while (list) {
> >> >>> +        /* The HMP output for streaming jobs is special because historically it
> >> >>> +         * was different from other job types so applications may depend on the
> >> >>> +         * exact string.
> >> >>> +         */
> >> >>
> >> >> Er, what? This is new code. What HMP clients use this string? I know
> >> >> that libvirt already got support for this before we implemented it, but
> >> >> shouldn't that be QMP only?
> >> >
> >> > Libvirt HMP uses this particular string, which turned out to be
> >> > sub-optimal once I realized we might support other types of block jobs
> >> > in the future.
> >> >
> >> > You can still build libvirt HMP-only by disabling the yajl library
> >> > dependency.  The approach I've taken is to make the interfaces available
> >> > over both HMP and QMP (and so has the libvirt-side code).
> >> >
> >> > In any case, we have defined both HMP and QMP.  Libvirt implements both
> >> > and I don't think there's a reason to provide only QMP.
> >> >
> >> > Luiz: For future features, are we supposed to provide only QMP
> >> > interfaces, not HMP?
> >>
> >> Of course, qemu should provide them as HMP command. But libvirt
> >> shouldn't use HMP commands. HMP is intended for human users, not as an
> >> API for management.
> >
> > That's correct.
> >
> > What defines if you're going to have a HMP version of a command is if
> > you expect it to be used by humans and if you do all its output and
> > arguments should be user friendly. You should never expect nor assume
> > it's going to be used by a management interface.
> 
> Okay, thanks Kevin and Luiz for explaining.  In this case I know it is
> used by a management interface because libvirt has code to use it.
> 
> I was my mistake to include the HMP side as part of the "API" but it's
> here now and I think we can live with this.

I need to fully review this series to ack or nack this, but unfortunately I've
had a busy week and will be on vacations for two weeks starting in a few hours.

I think it would be needed to have at least Kevin and Anthony or me acking this.