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

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

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.

I don't consider this a blocker though, so you pick whether to do this
or not.


> diff --git a/yank.h b/yank.h
> new file mode 100644
> index 0000000000..f1c8743b72
> --- /dev/null
> +++ b/yank.h
> @@ -0,0 +1,67 @@
> +

Missing license header

> +#ifndef YANK_H
> +#define YANK_H
> +
> +typedef void (YankFn) (void *opaque);
> +
> +/**
> + * yank_register_instance: Register a new instance.
> + *
> + * This registers a new instance for yanking. Must be called before any yank
> + * function is registered for this instance.
> + *
> + * This function is thread-safe.
> + *
> + * @instance_name: The globally unique name of the instance.
> + */
> +void yank_register_instance(char *instance_name);
> +
> +/**
> + * yank_unregister_instance: Unregister a instance.
> + *
> + * This unregisters a instance. Must be called only after every yank function
> + * of the instance has been unregistered.
> + *
> + * This function is thread-safe.
> + *
> + * @instance_name: The name of the instance.
> + */
> +void yank_unregister_instance(char *instance_name);
> +
> +/**
> + * yank_register_function: Register a yank function
> + *
> + * This registers a yank function. All limitations of qmp oob commands apply
> + * to the yank function as well.
> + *
> + * This function is thread-safe.
> + *
> + * @instance_name: The name of the instance
> + * @func: The yank function
> + * @opaque: Will be passed to the yank function
> + */
> +void yank_register_function(char *instance_name, YankFn *func, void *opaque);
> +
> +/**
> + * yank_unregister_function: Unregister a yank function
> + *
> + * This unregisters a yank function.
> + *
> + * This function is thread-safe.
> + *
> + * @instance_name: The name of the instance
> + * @func: func that was passed to yank_register_function
> + * @opaque: opaque that was passed to yank_register_function
> + */
> +void yank_unregister_function(char *instance_name, YankFn *func, void *opaque);
> +
> +/**
> + * yank_unregister_function: Generic yank function for iochannel
> + *
> + * This is a generic yank function which will call qio_channel_shutdown on the
> + * provided QIOChannel.
> + *
> + * @opaque: QIOChannel to shutdown
> + */
> +void yank_generic_iochannel(void *opaque);
> +#endif



Regards,
Daniel
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