Re: SO_REUSEADDR redux

["Paul D. Smith" <pausmith@nortelnetworks.com>]

%% Alan Cox <alan@lxorguk.ukuu.org.uk> writes:

  >> This application uses SO_REUSEADDR in conjunction with INADDR_ANY.  What
  >> it does is bind() to INADDR_ANY, then listen().  Then, it proceeds to
  >> bind (but _not_ listen) various other specific addresses.

  ac> That should be ok if its setting SO_REUSEADDR

I agree, and so does Solaris/FreeBSD, but Linux doesn't.  See below for
a test program.  Maybe I'm doing something screwed up.

-------------------------8>< snip ><8-------------------------
#include <stdio.h>
#include <errno.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>

#define MY_PORT     10000


int
main(int argc, char *argv[])
{
  int any_fd, this_fd;
  int val = 1;
  struct sockaddr_in addr;

  if ((any_fd = socket(PF_INET, SOCK_STREAM, 0)) < 0
      || fcntl(any_fd, F_SETFL, O_NONBLOCK) < 0
      || setsockopt(any_fd, SOL_SOCKET, SO_REUSEADDR, &val, sizeof val) < 0) {
    perror("setup(any)");
    return 1;
  }

  if ((this_fd = socket(PF_INET, SOCK_STREAM, 0)) < 0
      || fcntl(this_fd, F_SETFL, O_NONBLOCK) < 0
      || setsockopt(this_fd, SOL_SOCKET, SO_REUSEADDR, &val, sizeof val) < 0) {
    perror("setup(this)");
    return 1;
  }

  addr.sin_family = AF_INET;
  addr.sin_port = MY_PORT;
  memset(addr.sin_zero, 0, sizeof (addr.sin_zero));

  addr.sin_addr.s_addr = INADDR_ANY;

  if (bind(any_fd, (struct sockaddr *)&addr, sizeof (addr)) < 0) {
    perror("bind(any)");
    return 1;
  }

  if (listen(any_fd, 10) < 0) {
    perror("listen(any)");
    return 1;
  }

  addr.sin_addr.s_addr = INADDR_LOOPBACK;

  if (bind(this_fd, (struct sockaddr *)&addr, sizeof (addr)) < 0) {
    perror("bind(this)");
    return 1;
  }

  return 0;
}
-------------------------8>< snip ><8-------------------------

  solaris$ gcc -o reuseaddr{,.c} -lsocket -lnsl
  solaris$ ./reuseaddr

Works.  Now:

  linux$ gcc -o reuseaddr{,.c}
  linux$ ./reuseaddr
  bind(this): Cannot assign requested address

:(  The real code doesn't use LOOPBACK, of course.

This is Linux 2.2.17, but I tried with 2.2.18 too.  I haven't tried
2.4.x.


Thanks...

-- 
-------------------------------------------------------------------------------
 Paul D. Smith <psmith@baynetworks.com>    HASMAT--HA Software Methods & Tools
 "Please remain calm...I may be mad, but I am a professional." --Mad Scientist
-------------------------------------------------------------------------------
   These are my opinions---Nortel Networks takes no responsibility for them.
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