Re: [Qemu-devel] [PATCH 1/3] iothread: provide helpers for internal use

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

On Fri, Sep 22, 2017 at 04:56:10PM +0800, Peter Xu wrote:
> IOThread is a general framework that contains IO loop environment and a
> real thread behind.  It's also good to be used internally inside qemu.
> Provide some helpers for it to create iothreads to be used internally.
> 
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>  include/sysemu/iothread.h |  8 ++++++++
>  iothread.c                | 21 +++++++++++++++++++++
>  2 files changed, 29 insertions(+)
> 
> diff --git a/include/sysemu/iothread.h b/include/sysemu/iothread.h
> index d2985b3..b07663f 100644
> --- a/include/sysemu/iothread.h
> +++ b/include/sysemu/iothread.h
> @@ -46,4 +46,12 @@ AioContext *iothread_get_aio_context(IOThread *iothread);
>  void iothread_stop_all(void);
>  GMainContext *iothread_get_g_main_context(IOThread *iothread);
>  
> +/*
> + * Helpers used to allocate iothreads for internal use.  These
> + * iothreads will not be seen by monitor clients when query using
> + * "query-iothreads".
> + */
> +IOThread *iothread_create(const char *id, Error **errp);
> +void iothread_destroy(IOThread *iothread);
> +
>  #endif /* IOTHREAD_H */
> diff --git a/iothread.c b/iothread.c
> index 44c8944..74e400c 100644
> --- a/iothread.c
> +++ b/iothread.c
> @@ -354,3 +354,24 @@ GMainContext *iothread_get_g_main_context(IOThread *iothread)
>  
>      return iothread->worker_context;
>  }
> +
> +static Object *iothread_get_internal_parent(void)
> +{
> +    return container_get(object_get_root(), "/internal-iothreads");
> +}

I tend to think we might benefit from having this generalized in the
QOM API instead. We have object_get_objects_root() for things that
are created by the mgmt app / user via CLI / QMP.  A parallel method
object_get_internal_root() could be useful for cases like this where
we want to create user-creatable objects, but not have them be
visible to the mgmt app / user, as that would confuse the mgmt app.

Example for this scenario - libvirt calls query-iothreads to identify
IO thread PIDs, and would get very unhappy if the IOThread used by
the monitor would appear in that response, which is why Peter has
put it under /internal-iothreads. I think this scenario will apply
more broadly, so benefit from us having a general helper in QOM.


Regards,
Daniel
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