Re: [PATCH v2 01/17] vhost: fix messages error checks

[Ilya Maximets <i.maximets@samsung.com>]

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@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?

> 
>>> -        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;
>>>
> 
>