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

Maxime Coquelin maxime.coquelin at redhat.com
Wed Oct 3 16:39:23 CEST 2018



On 10/03/2018 11:07 AM, Ilya Maximets wrote:
> On 03.10.2018 11:32, Ilya Maximets wrote:
>> On 03.10.2018 11:02, Maxime Coquelin wrote:
>>>
>>>
>>> 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?
>>
>> Hmm. Yes, you're right. send_vhost_reply clears the VHOST_USER_NEED_REPLY
>> flag and vhost doesn't send replies twice.
>> Maybe some comment with clarifications needed here, or some more
>> refactoring to make this aspect more clear.
>>

Agree.
I'm adding a comment, I don't think a refactoring is required, and I
would be reluctant to add one more refactoring so close to the
integration deadline.

Does it work for you?

Thanks,
Maxime


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