popen2 popen call

popen2 popen call

[F. Heitkamp]

Hi,

I am using vanilla kernel 2.6.31-rc7, glibc 2.10.x on a Core 2 Duo system.

When the popen call is made in sshd/session.c I get a error from strerror 
of "Function not Implemented".  I googled a bit and found that there is 
sometimes an problem between the way the kernel and glibc are compiled 
that causes glibc not to find the popen2 call in the kernel.  The fix 
seemed to imply I need a certain processor choice when compiling the 
kernel.

Strangely, simple popen test programs seem to work OK.

Can anyone shed some light on this for me?  I would like to get this to 
work, so my X11 forwarding works in ssh.

BTW, kernels before 2.6.27 don't seem to cause the problem to manifest 
itself.

Thanks!

Fred

Re: popen2 popen call

[Andreas Schwab]

"F. Heitkamp" <heitkamp@ameritech.net> writes:

> When the popen call is made in sshd/session.c I get a error from
> strerror of "Function not Implemented".

Which function exactly returns this error?

> I googled a bit and found that there is sometimes an problem between
> the way the kernel and glibc are compiled that causes glibc not to
> find the popen2 call in the kernel.

There is no such thing as a popen2 syscall.

Andreas.

-- 
Andreas Schwab, schwab@redhat.com
GPG Key fingerprint = D4E8 DBE3 3813 BB5D FA84  5EC7 45C6 250E 6F00 984E
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Re: popen2 popen call

[heitkamp]

-------------- Original message from Andreas Schwab <schwab@redhat.com>: -------------- 


> "F. Heitkamp" writes: 
> 
> > When the popen call is made in sshd/session.c I get a error from 
> > strerror of "Function not Implemented". 
> 
> Which function exactly returns this error? 

In the openssh source distribution there is a file, session.c that uses popen, with the
ultimate purpose of fixing the .Xauthority file for X11 forwarding.  It uses popen to set the DISPLAY, MIT-MAGIC-COOKIE etc. via the shell I think, executing xauth.  In session.c popen is used three times under different conditions.  I put strerror calls where the popen call returns a NULL pointer to try to find out why the popen call fails.  I could post the section of code if you want to see.  I am not a professional programmer.

The gist of it is:

fp = popen( cmdstr, "w" );
if ( !fp )
  /* call strerror, errno */
> 
> There is no such thing as a popen2 syscall. 

OK.  I read in one of the messages, that glibc, passes the popen call to a ABI in the kernel. I have not looked at the code in glibc yet.

Fred

Re: popen2 popen call

[Ulrich Drepper]

On Thu, Aug 27, 2009 at 11:39, <heitkamp@ameritech.net> wrote:
> OK.  I read in one of the messages, that glibc, passes the popen call to a ABI in the kernel. I have not
> looked at the code in glibc yet.

popen uses pipe2.  There is fallback code to use pipe if necessary.
It's compiled out only of the libc assumes the kernel support is
available.

Re: popen2 popen call

[F. Heitkamp]

Ulrich Drepper wrote:
> On Thu, Aug 27, 2009 at 11:39,<heitkamp@ameritech.net>  wrote:
>    
>> OK.  I read in one of the messages, that glibc, passes the popen call to a ABI in the kernel. I have not
>> looked at the code in glibc yet.
>>      
>
> popen uses pipe2.  There is fallback code to use pipe if necessary.
> It's compiled out only of the libc assumes the kernel support is
> available.
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>    
OK.  I think I found the problem but how do I fix it?
Did I miss a kernel config option?
I got the code from the man page:
http://linux.die.net/man/2/pipe
http://manpages.courier-mta.org/htmlman2/pipe.2.html

bash-4.0$ gcc -o linux-pipe linux-pipe.c
/tmp/ccHHOYkD.o: In function `main':
linux-pipe.c:(.text+0x3b): warning: warning: pipe2 is not implemented 
and will always fail
bash-4.0$ ./linux-pipe ls
pipe: Function not implemented
bash-4.0$


#include <sys/wait.h>
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
int
main(int argc, char *argv[])
{
     int pfd[2];
     pid_t cpid;
     char buf;
     assert(argc == 2);
     if (pipe2(pfd) == -1) { perror("pipe"); exit(EXIT_FAILURE); }
     cpid = fork();
     if (cpid == -1) { perror("fork"); exit(EXIT_FAILURE); }
     if (cpid == 0) {    /* Child reads from pipe */
         close(pfd[1]);          /* Close unused write end */
         while (read(pfd[0], &buf, 1) > 0)
             write(STDOUT_FILENO, &buf, 1);
         write(STDOUT_FILENO, "\n", 1);
         close(pfd[0]);
         _exit(EXIT_SUCCESS);
     } else {            /* Parent writes argv[1] to pipe */
         close(pfd[0]);          /* Close unused read end */
         write(pfd[1], argv[1], strlen(argv[1]));
         close(pfd[1]);          /* Reader will see EOF */
         wait(NULL);             /* Wait for child */
         exit(EXIT_SUCCESS);
     }
}

Re: popen2 popen call

[Ulrich Drepper]

On Sat, Sep 5, 2009 at 10:39, F. Heitkamp<heitkamp@ameritech.net> wrote:
> linux-pipe.c:(.text+0x3b): warning: warning: pipe2 is not implemented and
> will always fail

you will get this warning if the glibc you're using was compiled
without appropriate kernel headers.  I.e., the definition of
__NR_pipe2 wasn't available.

Re: popen2 popen call

[F. Heitkamp]

Ulrich Drepper wrote:
> On Sat, Sep 5, 2009 at 10:39, F. Heitkamp<heitkamp@ameritech.net>  wrote:
>    
>> linux-pipe.c:(.text+0x3b): warning: warning: pipe2 is not implemented and
>> will always fail
>>      
>
> you will get this warning if the glibc you're using was compiled
> without appropriate kernel headers.  I.e., the definition of
> __NR_pipe2 wasn't available.
> --
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>
>    
Compiling glibc with newer headers worked!  Thank you all.

Fred