Re: [Qemu-devel] [PATCH 1/2] libvhost-user: support resuming vq->last_avail_idx based on used_idx

[Marc-André Lureau]

Hi

On Tue, Aug 29, 2017 at 5:09 PM, Michael S. Tsirkin <address@hidden> wrote:
> On Tue, Aug 29, 2017 at 05:04:34PM +0200, Marc-André Lureau wrote:
>> Hi
>>
>> On Tue, Aug 29, 2017 at 5:01 PM, Michael S. Tsirkin <address@hidden> wrote:
>> > On Tue, Aug 29, 2017 at 04:48:04PM +0200, Marc-André Lureau wrote:
>> >> This is the same workaround as commit 523b018dde3b765, which was lost
>> >> with libvhost-user transition in commit e10e798c85c2331.
>> >>
>> >> Signed-off-by: Marc-André Lureau <address@hidden>
>> >> ---
>> >>  contrib/libvhost-user/libvhost-user.h |  5 +++++
>> >>  contrib/libvhost-user/libvhost-user.c | 13 +++++++++++++
>> >>  2 files changed, 18 insertions(+)
>> >>
>> >> diff --git a/contrib/libvhost-user/libvhost-user.h 
>> >> b/contrib/libvhost-user/libvhost-user.h
>> >> index 53ef222c0b..aca71717c1 100644
>> >> --- a/contrib/libvhost-user/libvhost-user.h
>> >> +++ b/contrib/libvhost-user/libvhost-user.h
>> >> @@ -132,6 +132,7 @@ typedef void (*vu_set_features_cb) (VuDev *dev, 
>> >> uint64_t features);
>> >>  typedef int (*vu_process_msg_cb) (VuDev *dev, VhostUserMsg *vmsg,
>> >>                                    int *do_reply);
>> >>  typedef void (*vu_queue_set_started_cb) (VuDev *dev, int qidx, bool 
>> >> started);
>> >> +typedef bool (*vu_queue_resume_to_used_cb) (VuDev *dev, int qidx);
>> >>
>> >>  typedef struct VuDevIface {
>> >>      /* called by VHOST_USER_GET_FEATURES to get the features bitmask */
>> >> @@ -148,6 +149,10 @@ typedef struct VuDevIface {
>> >>      vu_process_msg_cb process_msg;
>> >>      /* tells when queues can be processed */
>> >>      vu_queue_set_started_cb queue_set_started;
>> >> +    /* If the queue must be resumed to vring.used->idx. */
>> >> +    /* This can help to support resuming on unmanaged exit/crash when
>> >> +     * the slave/driver processes elements in order. */
>> >> +    vu_queue_resume_to_used_cb queue_resume_to_used;
>> >>  } VuDevIface;
>> >>
>> >>  typedef void (*vu_queue_handler_cb) (VuDev *dev, int qidx);
>> >
>> > Let's consider: this is only safe if queue is processed in order.
>> > So I think that would be a better name for the field.
>> >
>> That's what the comment say already :)
>>
>> Which name do you suggest? vu_queue_is_processed_in_order?
>
> Something like this.
>
>> Does that
>> imply it should always resume?
>
> Not sure I understand the question.

If a "queue_is_processed_in_order", does that imply libvhost-user
should always resume it based on used_idx? I think it does, but the
correlation is less obvious than explicitly saying "resume_to_used".


-- 
Marc-André Lureau