Re: [dpdk-dev] [RFC 2/2] vhost: support vhost-user request only handled by external backend

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

On 2/27/19 2:15 PM, Ilya Maximets wrote:
> On 27.02.2019 13:02, Maxime Coquelin wrote:
>> External backends may have specific requests to handle, and so
>> we don't want the vhost-user lib to handle these requests as
>> errors.
>>
>> This patch also catch the case where a request is neither handled
>> by the external backend nor by the vhost library.
>>
>> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
>> ---
>>   lib/librte_vhost/vhost_user.c | 28 +++++++++++++++-------------
>>   1 file changed, 15 insertions(+), 13 deletions(-)
>>
>> diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
>> index 36c0c676d..bae5ef1cc 100644
>> --- a/lib/librte_vhost/vhost_user.c
>> +++ b/lib/librte_vhost/vhost_user.c
>> @@ -1924,27 +1924,29 @@ vhost_user_msg_handler(int vid, int fd)
>>   	}
>>   
>>   	ret = read_vhost_message(fd, &msg);
>> -	if (ret <= 0 || msg.request.master >= VHOST_USER_MAX) {
>> +	if (ret <= 0) {
>>   		if (ret < 0)
>>   			RTE_LOG(ERR, VHOST_CONFIG,
>>   				"vhost read message failed\n");
>> -		else if (ret == 0)
>> +		else
>>   			RTE_LOG(INFO, VHOST_CONFIG,
>>   				"vhost peer closed\n");
>> -		else
>> -			RTE_LOG(ERR, VHOST_CONFIG,
>> -				"vhost read incorrect message\n");
>>   
>>   		return -1;
>>   	}
>>   
>>   	ret = 0;
>> -	if (msg.request.master != VHOST_USER_IOTLB_MSG)
>> -		RTE_LOG(INFO, VHOST_CONFIG, "read message %s\n",
>> -			vhost_message_str[msg.request.master]);
>> -	else
>> -		RTE_LOG(DEBUG, VHOST_CONFIG, "read message %s\n",
>> -			vhost_message_str[msg.request.master]);
>> +	request = msg.request.master;
>> +	if (request < VHOST_USER_MAX && vhost_message_str[req]) {
>> +		if (request != VHOST_USER_IOTLB_MSG)
>> +			RTE_LOG(INFO, VHOST_CONFIG, "read message %s\n",
>> +				vhost_message_str[request]);
>> +		else if (
>> +			RTE_LOG(DEBUG, VHOST_CONFIG, "read message %s\n",
>> +				vhost_message_str[request]);
> 
> There is no need for the 'if' without the body.

Oops, indeed. I was pretty sure I did compile test it, but looking at
the history I didn't.

>> +	} else {
>> +		RTE_LOG(INFO, VHOST_CONFIG, "External request %d\n", request);
> 
> External requests could be annoying. Maybe we'll need to move them under DBG ?
> I'm not sure.

Fair point. I'll change to DBG.

>> +	}
>>   
>>   	ret = vhost_user_check_and_alloc_queue_pair(dev, &msg);
>>   	if (ret < 0) {
>> @@ -1960,7 +1962,7 @@ vhost_user_msg_handler(int vid, int fd)
>>   	 * inactive, so it is safe. Otherwise taking the access_lock
>>   	 * would cause a dead lock.
>>   	 */
>> -	switch (msg.request.master) {
>> +	switch (request) {
>>   	case VHOST_USER_SET_FEATURES:
>>   	case VHOST_USER_SET_PROTOCOL_FEATURES:
>>   	case VHOST_USER_SET_OWNER:
>> @@ -1985,6 +1987,7 @@ vhost_user_msg_handler(int vid, int fd)
>>   
>>   	}
>>   
>> +	ret = RTE_VHOST_MSG_RESULT_ERR;
> 
> This will break the 'vhost_crypto', because it has no 'pre_msg_handler'
> and master will skip to 'post_msg_handler', but it will not be called
> because current status is ERR.

Thanks for catching it.

> Maybe it's easier to introduce RTE_VHOST_MSG_RESULT_NOT_HANDLED and convert
> it to ERR before the reply ?
> This will require changing the pre_msg_handlers to return
> RTE_VHOST_MSG_RESULT_NOT_HANDLED if message wasn't recognized.
> And we'll possibly be able to drop the 'skip_master' in this case.

Ok, that means breaking the API, but it is still experimental so not a
blocker.

I like the idea because it would also make it possible to add some debug 
prints.

I'll post new iteration this morning.

Thanks,
Maxime

>>   	if (dev->extern_ops.pre_msg_handle) {
>>   		ret = (*dev->extern_ops.pre_msg_handle)(dev->vid,
>>   				(void *)&msg, &skip_master);
>> @@ -1997,7 +2000,6 @@ vhost_user_msg_handler(int vid, int fd)
>>   			goto skip_to_post_handle;
>>   	}
>>   
>> -	request = msg.request.master;
>>   	if (request > VHOST_USER_NONE && request < VHOST_USER_MAX) {
>>   		if (!vhost_message_handlers[request])
>>   			goto skip_to_post_handle;
>>