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List:       xfree86-devel
Subject:    XDMCP broadcast trouble (was: XDMCP problems)
From:       Mario Klebsch <mario () klebsch ! de>
Date:       2003-12-31 18:33:48
Message-ID: DFDA55E1-3BBF-11D8-9375-000A9586F10A () klebsch ! de
[Download RAW message or body]

Hi!

> -broadcast does not send XDMCP requests to a broadcast address

I have traced this one a little bit further. I wrote a small test 
program:

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <sys/ioctl.h>
#include <net/if.h>

int fd;
struct ifreq req;

int main(int argc, char *argv[])
{
   fd=socket(SOCK_STREAM, PF_INET, 0);
   if (fd<0)
     {
       perror("socket");
       exit(-1);
     }

   strcpy(req.ifr_name,"en1");
   ((struct sockaddr_in *) 
&req.ifr_addr)->sin_addr.s_addr=htonl(0x12345678);
printf("prior to ioctl(): %s, %s\n", req.ifr_name,
        inet_ntoa(((struct sockaddr_in *) &req.ifr_addr)->sin_addr));
   if (ioctl(fd, SIOCGIFBRDADDR, &req)<0)
     {
       perror("ioctl");
       exit(-1);
     }
printf("after ioctl(): %s, %s\n", req.ifr_name,
        inet_ntoa(((struct sockaddr_in *) &req.ifr_addr)->sin_addr));
}

it does create a socket and then tries to determine the broadcast 
address. I initialize ifr_addr with some predefined nonsense and then I 
found, that this nonsense is not overwritten by the ioctl() nor is any 
error code returned. :-( On my linux box, an invalid argument error is 
returned.

To use SIOCGIFBRDADDR, fd must be the fd of a datagram socket, on 
MacOSX as well as on Linux. So the code in 
xc/programs/Xserver/os/access.c near line 868, that does not work on 
MacOSX, will not work on linux, too. At least it will not register the 
wrong address, since linux correctly returns an error code.

73, Mario
-- 
Mario Klebsch                                      mario@klebsch.de
PGP-Key available at http://www.klebsch.de/public.key
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