Re: [PATCH] vhost: fix MQ fails to startup

[Yuanhan Liu <yuanhan.liu@linux.intel.com>]

On Thu, Apr 27, 2017 at 02:34:53PM +0800, Zhiyong Yang wrote:
> vhost since dpdk17.02 + qemu2.7 and above will cause failures of
> new connection when negotiating to set MQ. (one queue pair works
> well).Because there exist some bugs in qemu code when introducing
> VHOST_USER_PROTOCOL_F_REPLY_ACK to qemu. when dealing with the vhost
> message VHOST_USER_SET_MEM_TABLE for the second time, qemu indeed
> doesn't send the messge (The message needs to be sent only once)but
> still will be waiting for dpdk's reply ack, then, qemu is always
> freezing. DPDK code works in the right way. But the feature 
> VHOST_USER_PROTOCOL_F_REPLY_ACK has to be disabled by default at the
> dpdk side in order to avoid the feature support of DPDK + qemu at
> the same time. if doing like that, MQ can works well.
...
> Once Qemu bugs
> have been fixed and upstreamed, we can enable it.

As I have said, we should not enable it again, because there are already
few buggy QEMU releases out. We should make sure DPDK also works well with
them.

> Fixes: 73c8f9f69c6c("vhost: introduce reply ack feature")

That commit does nothing wrong. It's QEMU being buggy. That said, I will
not add such fixline. I will also use "workaround" instead of "fix" in
the title.

Also, this patch should be backported to stable release. So, you should
add:
	Cc: stable@dpdk.org

Besides, please reformat you commit log a bit. For example, add space
after punctuation, use paragraph as possible, etc.

> 
> Reported-by: Loftus, Ciara <ciara.loftus@intel.com>

No "," is allowed.

> Signed-off-by: Zhiyong Yang <zhiyong.yang@intel.com>
> ---
>  lib/librte_vhost/vhost_user.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/lib/librte_vhost/vhost_user.h b/lib/librte_vhost/vhost_user.h
> index 2ba22db..a3d2900 100644
> --- a/lib/librte_vhost/vhost_user.h
> +++ b/lib/librte_vhost/vhost_user.h
> @@ -52,7 +52,7 @@
>  #define VHOST_USER_PROTOCOL_FEATURES	((1ULL << VHOST_USER_PROTOCOL_F_MQ) | \
>  					 (1ULL << VHOST_USER_PROTOCOL_F_LOG_SHMFD) |\
>  					 (1ULL << VHOST_USER_PROTOCOL_F_RARP) | \
> -					 (1ULL << VHOST_USER_PROTOCOL_F_REPLY_ACK) | \
> +					 (0ULL << VHOST_USER_PROTOCOL_F_REPLY_ACK) | \
>  					 (1ULL << VHOST_USER_PROTOCOL_F_NET_MTU))

I think you might want to add a simple comment here, something like

    /*
     * disable REPLY_ACK feature to workaround the buggy QEMU implementation.
     * Proved buggy QEMU includes v2.7 - v2.9.
     */

So, please send v2?

	--yliu