>> Okay. If callers must already handle 0 as a valid return code, then
>> it is fine to add another case that does this.
>>
>> The extra branch in the hot path is still rather unfortunately. Could
>> this be integrated in the existing if (nonblock) branch below?
>
> that's where I first started. it got even hairier because the
> callers expect a retval of 0 (-EAGAIN threw rds-stress into an
> infinite loop of continulally trying to recv) and the end result
> was just confusing code with the same number of branches..
I do mean returning 0 instead of -EAGAIN if control data is ready.
Something like
@@ -611,7 +611,8 @@ int rds_recvmsg(struct socket *sock, struct msghdr
*msg, size_t size,
if (!rds_next_incoming(rs, &inc)) {
if (nonblock) {
- ret = -EAGAIN;
+ ncookies = rds_recvmsg_zcookie(rs, msg);
+ ret = ncookies ? 0 : -EAGAIN;
break;
}
By the way, the put_cmsg is unconditional even if the caller did
not supply msg_control. So it is basically no longer safe to ever
call read, recv or recvfrom on a socket if zerocopy notifications
are outstanding.
It is possible to check msg_controllen before even deciding whether
to try to dequeue notifications (and take the lock). I see that this is
not common. But RDS of all cases seems to do this, in
rds_notify_queue_get:
max_messages = msghdr->msg_controllen /
CMSG_SPACE(sizeof(cmsg));
