Re: [PATCH v4 1/4] Introduce yank feature

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

On Fri, Jun 19, 2020 at 04:23:50PM +0200, Lukas Straub wrote:
> On Tue, 16 Jun 2020 15:39:57 +0100
> Daniel P. Berrangé <berrange@redhat.com> wrote:
> 
> > On Mon, May 25, 2020 at 05:44:23PM +0200, Lukas Straub wrote:
> > > The yank feature allows to recover from hanging qemu by "yanking"
> > > at various parts. Other qemu systems can register themselves and
> > > multiple yank functions. Then all yank functions for selected
> > > instances can be called by the 'yank' out-of-band qmp command.
> > > Available instances can be queried by a 'query-yank' oob command.
> > > 
> > > Signed-off-by: Lukas Straub <lukasstraub2@web.de>
> > > ---
> > >  qapi/misc.json |  45 +++++++++++++
> > >  yank.c         | 174 +++++++++++++++++++++++++++++++++++++++++++++++++
> > >  yank.h         |  67 +++++++++++++++++++
> > >  3 files changed, 286 insertions(+)
> > >  create mode 100644 yank.c
> > >  create mode 100644 yank.h  
> > 
> > > +void yank_register_function(char *instance_name, YankFn *func, void *opaque)
> > > +{
> > > +    struct YankInstance *instance;
> > > +    struct YankFuncAndParam *entry;
> > > +
> > > +    qemu_mutex_lock(&lock);
> > > +    instance = yank_find_instance(instance_name);
> > > +    assert(instance);
> > > +
> > > +    entry = g_slice_new(struct YankFuncAndParam);
> > > +    entry->func = func;
> > > +    entry->opaque = opaque;
> > > +
> > > +    QLIST_INSERT_HEAD(&instance->yankfns, entry, next);
> > > +    qemu_mutex_unlock(&lock);
> > > +}
> > > +
> > > +void yank_unregister_function(char *instance_name, YankFn *func, void *opaque)
> > > +{
> > > +    struct YankInstance *instance;
> > > +    struct YankFuncAndParam *entry;
> > > +
> > > +    qemu_mutex_lock(&lock);
> > > +    instance = yank_find_instance(instance_name);
> > > +    assert(instance);
> > > +
> > > +    QLIST_FOREACH(entry, &instance->yankfns, next) {
> > > +        if (entry->func == func && entry->opaque == opaque) {
> > > +            QLIST_REMOVE(entry, next);
> > > +            g_slice_free(struct YankFuncAndParam, entry);
> > > +            qemu_mutex_unlock(&lock);
> > > +            return;
> > > +        }
> > > +    }
> > > +
> > > +    abort();
> > > +}  
> > 
> > Since the NBD impl no longer needs to register multiple different functions
> > on the same insance_nane, these methods could be be simplified, to only
> > accept a single function, instead of keeping a whole list. This would avoid
> > need to pass a function into the unregister() method at all.
> 
> Multiple yank functions are still needed for multifd migration.

Oh I missed that subtlety, so fine to ignore my suggestion.

Regards,
Daniel
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