pseudo tty stderr capture problem.
From: Min Shei (minshei_at_hotmail.com)
Date: 07/16/03
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Date: 15 Jul 2003 16:07:29 -0700
Hi, All,
I was trying to make a simple pseudo tty program to capture the stdout
and stderr from the child process to avoid the stdout buffering
problem. The following is a little program I found on one new group
here (written by Richard Tobin, 1990). However, this program captures
the child's stdout very well. But I just couldn't make it work for the
stderr of the child process. My platform is Solaris 2.7.
Has anyone here had the same problem? The program could be compiled
by:
cc -o nobuf nobuf.c pseudopipe.c
And if you run "./nobuf ls no-such-file", you should get message like
"no-such-file: No such file or directory". But there is not.
I just couldn't figure out what is wrong with this program. :(
Please help.
Thanks in advance.
Min
----------------------------------- nobuf.c
----------------------------------
/* A program to defeat buffering by stdio when the output is a pipe.
* nobuf program args ...
* runs the program with its standard input, output, and error
connected
* to a pseudo-terminal. It transfers data between the
pseudo-terminal
* and the real standard input etc. Since the program sees its output
is
* a terminal, it won't buffer it.
*
* Richard Tobin, 1990. You may redistribute this program freely if
this
* whole comment remains intact.
*/
#include <stdlib.h>
#include <errno.h>
#include <signal.h>
#include <sys/file.h>
#include <sys/ioctl.h>
#include <signal.h>
#include <unistd.h>
int dead_baby(); /* called when child exits */
int pty, ifds0;
main(argc, argv)
int argc;
char *argv[];
{
int ptyfds[2];
pseudopipe(ptyfds); /* create pty to talk to child */
ttymodes(ptyfds[0]);
signal(SIGCHLD, dead_baby); /* so we can exit when child does */
subprocess(&argv[1], ptyfds); /* start up the subshell */
close(ptyfds[0]); /* parent doesn't need it */
pty = ptyfds[1];
transfer();
}
/* fork and exec the process in argv */
subprocess(argv, ptyfds)
char **argv;
int ptyfds[2];
{
int tty;
if(fork() != 0) return;
/* close files child doesn't want */
close(ptyfds[1]);
close(0);
close(1);
close(2);
/* get rid of controlling terminal */
tty = open("/dev/tty", O_RDWR, 0);
ioctl(tty, TIOCNOTTY, 0);
close(tty);
/* set up pty as std input, output, error */
dup2(ptyfds[0], 0);
dup2(ptyfds[0], 1);
dup2(ptyfds[0], 2);
close(ptyfds[0]);
/* run the process */
execvp(argv[0], argv);
write(2, "exec failed\n", 12);
_exit(1);
}
/* set the pseudo terminal to fairly sane modes */
ttymodes(pty)
int pty;
{
static struct sgttyb sgtty = {B9600, B9600, 255, 255, EVENP|ODDP};
static struct tchars tchars = {255, 255, 255, 255, 4, 255};
ioctl(pty, TIOCSETP, &sgtty);
ioctl(pty, TIOCSETC, &tchars);
}
/* transfer characters between standard input/output and pty */
transfer()
{
int ifds, nread;
char buf[256], ctld=4;
extern int errno;
ifds0 = (1 << 0) | (1 << pty); /* listen to real and pseudo ttys */
while(ifds0 != 0)
{
ifds = ifds0;
if(select(pty+1, &ifds, (int *)0, (int *)0, (struct timeval *)0)
< 0)
{
if(errno == EINTR)
continue;
else
{
perror("select");
exit(1);
}
}
if(ifds & (1<<0))
{
nread = read(0, buf, 256); /* from tty to process */
if(nread > 0)
write(pty, buf, nread);
else if(nread == 0)
write(pty, &ctld, 1); /* writing zero bytes doesn't work
*/
else
ifds0 &= ~(1 << 0);
}
if(ifds & (1 << pty))
{
nread = read(pty, buf, 256); /* from process to tty */
if(nread >= 0)
write(1, buf, nread);
else
ifds0 &= ~(1 << pty);
}
}
while(1)
sigpause(0); /* wait for child to exit */
}
/* child process exited - do any remaining i/o and exit */
dead_baby()
{
char buf[256];
int nread;
while(ioctl(pty, FIONREAD, &nread) == 0 && nread > 0)
{
nread = read(pty, buf, 256);
write(1, buf, nread);
}
exit(0);
}
-------------------------------- pseudopipe.c
-----------------------------
/* like pipe(2) but uses pseudo-terminals. consequently, the
connection
* is bi-directional, and will appear as a terminal to any forked
process.
* copyright (C) 1986 Richard M Tobin
* you may freely distribute/modify this provided this whole comment
remains
* intact.
*/
#include <sys/types.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <strings.h>
#include <stdio.h>
/* pseudopipe puts two file descriptors in its argument array. fd[0]
is the
* slave side of a pseudo-terminal, fd[1] is the master side. to talk
to a
* child process, dup fd[0] onto file descriptors 0, 1 and 2.
* if anything goes wrong (probably no free pty) -1 is returned.
*/
int pseudopipe(fd)
int fd[2];
{
char pty_master[128], pty_slave[128];
#define masterfd fd[1]
#define slavefd fd[0]
FILE *cons;
int start=0;
masterfd = findpty(pty_master, pty_slave, &start);
if(masterfd < 0) return -1;
slavefd = open(pty_slave, O_RDWR, 0);
if(slavefd >= 0) return 0;
return -1;
#undef masterfd
#undef slavefd
}
/* findpty find a free pseudo-terminal, and opens the master side of
it.
* the arguments are filled in to be the paths of the master and
slave.
*/
#define MASTER "/dev/ptyXY"
#define SLAVE "/dev/ttyXY"
findpty(master_path, slave_path, ptyno)
char *master_path, *slave_path;
int *ptyno;
{
struct stat statbuf;
char c1;
int i, master;
strcpy(master_path, MASTER);
strcpy(slave_path, SLAVE );
/* the pseudo-ttys are /dev/ptyXY, where X is p,q,or r and Y is a
* hex digit. There are usually 16, 32 or 48 so we check for the
* of /dev/ptyX0 before trying to open them all.
*/
for(; *ptyno <= ('s'-'p') * 16; ++*ptyno)
{
master_path[strlen(MASTER)-2] = *ptyno / 16 + 'p';
master_path[strlen(MASTER)-1] = "0123456789abcdef"[*ptyno & 15];
master = open(master_path,O_RDWR);
if(master < 0) continue;
slave_path[strlen(SLAVE)-2] = master_path[strlen(MASTER)-2];
slave_path[strlen(SLAVE)-1] = master_path[strlen(MASTER)-1];
return master;
}
return -1;
}
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