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Groups > comp.os.linux.development.apps > #682

Re: Linux O_NONBLOCK bug/ quirk

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unixb4coffee <unixb4coffee@gmail.com> writes:
> On 04/03/2014 08:36 AM, Rainer Weikusat wrote:
>> unixb4coffee <unixb4coffee@gmail.com> writes:
>>> On 03/28/2014 01:12 PM, Rainer Weikusat wrote:
>>>> Rainer Weikusat <rweikusat@mobileactivedefense.com> writes:

[...]

>>>> ------------
>>>> #include <fcntl.h>
>>>> #include <string.h>
>>>> #include <sys/socket.h>
>>>> #include <sys/un.h>
>>>>
>>>> int main(void)
>>>> {
>>>>       struct sockaddr_un sun;
>>>>       int fd;
>>>>
>>>>       fd = socket(AF_UNIX, SOCK_DGRAM, 0);
>>>>       sun.sun_family = AF_UNIX;
>>>>       strncpy(sun.sun_path, "/tmp/bla", sizeof(sun.sun_path));
>>>>       bind(fd, (struct sockaddr *)&sun, sizeof(sun));
>>>>
>>>>       if (fork() == 0) recv(fd, &fd, sizeof(fd), 0);
>>>>
>>>>       sleep(1);
>>>>
>>>>       recv(fd, &fd, sizeof(fd), MSG_DONTWAIT);
>>>>
>>>>       return 0;
>>>> }
>>>> -------------

[...]

>>> But hangs aren't that unusual if a program doesn't take care to monitor
>>> the forked processes' status.  It also doesn't really say anything about the
>>> connection's state, or whether it's still possible to monitor it.
>>
>> There is no connection here, just a datagram socket shared by multiple
>> threads of execution.
>
> The bind () call gives the connection endpoints.

Not really. It binds a protocol address to a socket. In this case,
that's a filename. But the socket is a datagram socket (SOCK_DGRAM) and
thus, connection-less.

> A more basic approach might be to use sendto () and recvfrom (),
> though I'm not sure that would have any effect on socket sharing -

None, obviously. That's also somewhat besides the point because the code
included above was supposed to demonstrate 'an unfortunate property' of
the Linux AF_UNIX SOCK_DGRAM implementation aka 'a bug'.

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Thread

Linux O_NONBLOCK bug/ quirk Rainer Weikusat <rweikusat@mobileactivedefense.com> - 2014-03-27 15:26 +0000
  Re: Linux O_NONBLOCK bug/ quirk crankypuss <crankypuss@nomail.invalid> - 2014-03-28 02:08 -0600
    Re: Linux O_NONBLOCK bug/ quirk Rainer Weikusat <rweikusat@mobileactivedefense.com> - 2014-03-28 12:45 +0000
      Re: Linux O_NONBLOCK bug/ quirk crankypuss <crankypuss@nomail.invalid> - 2014-03-29 05:19 -0600
  Re: Linux O_NONBLOCK bug/ quirk Rainer Weikusat <rweikusat@mobileactivedefense.com> - 2014-03-28 20:12 +0000
    Re: Linux O_NONBLOCK bug/ quirk unixb4coffee <unixb4coffee@gmail.com> - 2014-04-02 11:13 -0700
      Re: Linux O_NONBLOCK bug/ quirk Rainer Weikusat <rweikusat@mobileactivedefense.com> - 2014-04-03 16:36 +0100
        Re: Linux O_NONBLOCK bug/ quirk unixb4coffee <unixb4coffee@gmail.com> - 2014-04-03 11:43 -0700
          Re: Linux O_NONBLOCK bug/ quirk Rainer Weikusat <rweikusat@mobileactivedefense.com> - 2014-04-03 21:31 +0100
  Re: Linux O_NONBLOCK bug/ quirk Lusotec <nomail@nomail.not> - 2014-03-28 23:13 +0000
    Re: Linux O_NONBLOCK bug/ quirk Richard Kettlewell <rjk@greenend.org.uk> - 2014-03-29 11:15 +0000
    Re: Linux O_NONBLOCK bug/ quirk Rainer Weikusat <rweikusat@mobileactivedefense.com> - 2014-03-30 19:42 +0100
    Re: Linux O_NONBLOCK bug/ quirk Rainer Weikusat <rweikusat@mobileactivedefense.com> - 2014-04-16 12:42 +0100
      Re: Linux O_NONBLOCK bug/ quirk Rainer Weikusat <rweikusat@mobileactivedefense.com> - 2014-04-16 13:36 +0100

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