Jan Kiszka wrote:
> Gilles Chanteperdrix wrote:
>> - rtnet-check-receiving.diff
>
>> @@ -375,13 +379,23 @@ ssize_t rt_udp_recvmsg(struct rtdm_dev_c
>> struct udphdr *uh;
>> struct sockaddr_in *sin;
>> nanosecs_rel_t timeout = sock->timeout;
>> - int ret;
>> + int ret, index;
>> + rtdm_lockctx_t context;
>>
>>
>> /* non-blocking receive? */
>> if (testbits(msg_flags, MSG_DONTWAIT))
>> timeout = -1;
>>
>> + rtdm_lock_get_irqsave(&udp_socket_base_lock, context);
>> + if ((index = sock->prot.inet.reg_index) < 0) {
>> + rtdm_lock_put_irqrestore(&udp_socket_base_lock, context);
>> + /* socket is being closed */
>> + return -EBADF;
>> + }
>> + port_registry[index].receiving = 1;
>> + rtdm_lock_put_irqrestore(&udp_socket_base_lock, context);
>> +
>
> This is the only part of the patch I don't like. I don't want to add
> another lock site to the RX path. I see the problem, but I think we need
> some other solution. Maybe something that disables reception, and thus
> unwanted buffer consumption.Well, I was too quick. There is another thing I don't like about this patch: It breaks valid use cases. Consider some application creating a socket first, then sending some message, next doing something else (or being preempted for a while), and finally calling into the recvmsg functions. With your change a potential reply to that sent-out message could have been dropped in the meantime because the socket was not yet marked as 'receiving'. Not good. We need an alternative approach, something that either set ups two buffer pools (but that might be costly memory-wise) or something that allows an application to actively disable reception on a socket. Given that your case is not a common issue, I would vote for the latter direction. Jan
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