Re: [dpdk-dev] [PATCH v4 04/19] vhost: fix payload size of reply

[Maxime Coquelin <maxime.coquelin@redhat.com>]

On 10/09/2018 12:21 PM, Tiwei Bie wrote:
> On Mon, Oct 08, 2018 at 05:25:42PM +0200, Maxime Coquelin wrote:
>> QEMU doesn't expect any payload for the reply of
>> VHOST_USER_SET_LOG_BASE request, so don't send any.
>> Note that the Vhost-user specification isn't clear about
>> it and would need to be fixed.
>>
>> Fixes: 54f9e32305d4 ("vhost: handle dirty pages logging request")
>> Cc: stable@dpdk.org
>>
>> Reported-by: Ilya Maximets <i.maximets@samsung.com>
>> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
>> Acked-by: Ilya Maximets <i.maximets@samsung.com>
>> ---
>>   lib/librte_vhost/vhost_user.c | 6 +++++-
>>   1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
>> index 7f3e86778..71a0e7dd7 100644
>> --- a/lib/librte_vhost/vhost_user.c
>> +++ b/lib/librte_vhost/vhost_user.c
>> @@ -1296,7 +1296,11 @@ vhost_user_set_log_base(struct virtio_net **pdev, struct VhostUserMsg *msg)
>>   	dev->log_base = dev->log_addr + off;
>>   	dev->log_size = size;
>>   
>> -	msg->size = sizeof(msg->payload.u64);
>> +	/*
>> +	 * The spec is not clear about it (yet), but QEMU doesn't expect
>> +	 * any payload in the reply.
>> +	 */
>> +	msg->size = 0;
> 
> I think the spec is clear about it that no payload is
> expected in the reply:
> 
> https://github.com/qemu/qemu/blob/7c69b7c84964/docs/interop/vhost-user.txt#L496
It isn't really clear because there are two cases[0]:
1. VHOST_USER_PROTOCOL_F_LOG_SHMFD not negotiated: In this case no reply
    has to be sent.
2. VHOST_USER_PROTOCOL_F_LOG_SHMFD negotiated: In this case reply with
    empty payload hsa to be sent.

[0]: 
https://github.com/qemu/qemu/blob/7c69b7c849641a39ba3defa40d384a2ba24cd7a2/docs/interop/vhost-user.txt#L177

> But below line in the spec needs to be fixed:
> 
> https://github.com/qemu/qemu/blob/7c69b7c84964/docs/interop/vhost-user.txt#L495

Indeed.

> 
>>   
>>   	return VH_RESULT_REPLY;
>>   }
>> -- 
>> 2.17.1
>>