Re: Wierd listen/connect: accept queue never fills up

[Ivan Pulleyn]

What was the sysctl value for net.ipv4.tcp_syn_max_backlog set to
while running this test? That's the value you are testing, not the
listen() queue size.

Ivan...

On 27 Nov 2002, Philippe Troin wrote:

> [Andi, I've CC'ed you since you're listed as the author of the `new
> listen' code in net/ipv4/tcp_ipv4.c]
> 
> Seen on linux 2.4.20rc2.
> 
> This program is always able to establish new connections to itself:
> the accept queue never fills up and connections always succeed
> (although they take quite some time after the first four):
> 
>   #include <stdio.h>
>   #include <sys/types.h>
>   #include <sys/socket.h>
>   #include <netinet/in.h>
> 
>   int main(void)
>   {
>     int fd;
>     struct sockaddr_in sin;
>     socklen_t sinlen;
> 
>     if ((fd = socket(PF_INET, SOCK_STREAM, 0)) == -1)
>       perror("socket"), exit(1);
> 
>     sin.sin_family      = AF_INET;
>     sin.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
>     sin.sin_port	      = htons(0);
>     if (bind(fd, (struct sockaddr*)&sin, sizeof(sin)) == -1)
>       perror("bind"), exit(1);
>     if (listen(fd, 1) == -1)
>       perror("listen"), exit(1);
> 
>     sinlen = sizeof(sin);
>     getsockname(fd, (struct sockaddr*)&sin, &sinlen);
> 
>     while (1)
>       {
>         int fdc;
> 
>         if ((fdc = socket(PF_INET, SOCK_STREAM, 0)) == -1)
>   	perror("socket"), exit(1);
>         printf("%c", connect(fdc, (struct sockaddr*)&sin, sinlen) == -1
>   	     ? 'F' : '.');
>         fflush(stdout);
>       }
> 
>     exit(0);
>   }
> 
> I've tried enabling and disabling tcp_syncookies, without any effect.
> 
> The same program starts returning errors after two successful connects
> on Solaris and one on HP-UX. Linux keeps returning new connections...
> 
> Phil.
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