On 10/24/2016, 03:03 PM, Eric Dumazet wrote:
> On Mon, 2016-10-24 at 14:54 +0200, Jiri Slaby wrote:
>> Hello,
>>
>> as per man 7 udp:
>> In order to receive packets, the socket can be bound to
>> a local address first by using bind(2). Otherwise,
>> the socket layer will automatically assign a free local
>> port out of the range defined by /proc/sys/net/ipv4
>> /ip_local_port_range and bind the socket to INADDR_ANY.
>>
>> I did not know that bind is unneeded, so I tried that. But it does not
>> work with this piece of code:
>> int main()
>> {
>> char buf[128];
>> int fd = socket(AF_INET, SOCK_DGRAM, 0);
>> recv(fd, buf, sizeof(buf), 0);
>> }
>
> autobind makes little sense at recv() time really.
>
> How an application could expect to receive a frame to 'some socket'
> without even knowing its port ?
For example
struct sockaddr_storage sa;
socklen_t slen = sizeof(sa);
recv(fd, buf, sizeof(buf), MSG_DONTWAIT);
getsockname(fd, (struct sockaddr *)&sa, &slen);
recv(fd, buf, sizeof(buf), 0);
works.
> How useful would that be exactly ?
No need for finding a free port and checking, for example.
> How TCP behaves ?
TCP is a completely different story. bind is documented to be required
there. (And listen and accept.)
> I would say, fix the documentation if it is not correct.
I don't have a problem with either. I have only found, that the
implementation differs from the documentation :). Is there some
supervisor documentation (like POSIX) which should we be in conformance to?
thanks,
--
js
suse labs
