[dpdk-stable] [PATCH v2 01/17] vhost: fix messages error checks

[Maxime Coquelin]

On 10/03/2018 09:57 AM, Ilya Maximets wrote:
> On 03.10.2018 10:50, Maxime Coquelin wrote:
>>
>>
>> On 10/02/2018 04:15 PM, Ilya Maximets wrote:
>>> On 02.10.2018 12:36, Maxime Coquelin wrote:
>>>> Return of message handling has now changed to an enum that can
>>>> take non-negative value that is not zero in case a reply is
>>>> needed. But the code checking the variable afterwards has not
>>>> been updated, leading to success messages handling being
>>>> treated as errors.
>>>>
>>>> Fixes: 4e601952cae6 ("vhost: message handling implemented as a callback array")
>>>>
>>>> Signed-off-by: Maxime Coquelin <maxime.coquelin at redhat.com>
>>>> ---
>>>>    lib/librte_vhost/vhost_user.c | 6 +++---
>>>>    1 file changed, 3 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
>>>> index 7ef3fb4a4..060b41893 100644
>>>> --- a/lib/librte_vhost/vhost_user.c
>>>> +++ b/lib/librte_vhost/vhost_user.c
>>>> @@ -1783,7 +1783,7 @@ vhost_user_msg_handler(int vid, int fd)
>>>>        }
>>>>      skip_to_post_handle:
>>>> -    if (!ret && dev->extern_ops.post_msg_handle) {
>>>> +    if (ret != VH_RESULT_ERR && dev->extern_ops.post_msg_handle) {
>>>>            uint32_t need_reply;
>>>>              ret = (*dev->extern_ops.post_msg_handle)(
>>>> @@ -1800,10 +1800,10 @@ vhost_user_msg_handler(int vid, int fd)
>>>>            vhost_user_unlock_all_queue_pairs(dev);
>>>>          if (msg.flags & VHOST_USER_NEED_REPLY) {
>>>
>>> Maybe we need to reply here only if we didn't reply
>>> already (not VH_RESULT_REPLY) ? Otherwise, we could
>>> reply twice (with payload and with return code).
>>
>> Well, if the master sets this bit, it means it is waiting for
>> a "reply-ack", so not sending it would cause the master to wait
>> forever.
>>
>> It is the master responsibility to not set this bit for requests
>> already expecting a non "reply-ack" reply (as you fixed it for
>> postcopy's set mem table case).
> 
> vhost-user docs in QEMU says:
> "
> For the message types that already solicit a reply from the client, the
> presence of VHOST_USER_PROTOCOL_F_REPLY_ACK or need_reply bit being set brings
> no behavioural change.
> "
> i.e. even if QEMU sets the need_reply flag, vhost should not reply twice.
> Am I missing something?

Oh, right. Thanks for pointing it out.

So coming back to the DPDK implementation, I just had a look again, and 
it seems that we don't send a reply twice, as send_vhost_reply takes
care of clearing the VHOST_USER_NEED_REPLY flag.
Do you confirm my understanding is correct?

>>
>>>> -        msg.payload.u64 = !!ret;
>>>> +        msg.payload.u64 = ret == VH_RESULT_ERR;
>>>>            msg.size = sizeof(msg.payload.u64);
>>>>            send_vhost_reply(fd, &msg);
>>>> -    } else if (ret) {
>>>> +    } else if (ret == VH_RESULT_ERR) {
>>>>            RTE_LOG(ERR, VHOST_CONFIG,
>>>>                "vhost message handling failed.\n");
>>>>            return -1;
>>>>
>>
>>