Date: Thu, 7 Jul 2005 11:14:25 +0530 From: Dipjyoti Saikia <dipjyoti.saikia@gmail.com> To: Dan Nelson <dnelson@allantgroup.com> Cc: freebsd-hackers@freebsd.org Subject: Re: thread-safe popen Message-ID: <dcbc809d050706224410fff9c4@mail.gmail.com> In-Reply-To: <20050705143814.GA38925@dan.emsphone.com> References: <dcbc809d05070503454a259f88@mail.gmail.com> <20050705143814.GA38925@dan.emsphone.com>
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Hi ,
Please find the code snippet of popen() from the source code that I
have (We are working on an OS that is derived from FreeBSD 4.1) . I
don't think I have the thread safe version .
-------------------------
FILE *
popen(command, type)
const char *command, *type;
{
struct pid *cur;
FILE *iop;
int pdes[2], pid, twoway;
char *argv[4];
struct pid *p;
/*
* Lite2 introduced two-way popen() pipes using socketpair().
* FreeBSD's pipe() is bidirectional, so we use that.
*/
if (strchr(type, '+')) {
twoway =3D 1;
type =3D "r+";
} else {
twoway =3D 0;
if ((*type !=3D 'r' && *type !=3D 'w') || type[1])
return (NULL);
}
if (pipe(pdes) < 0)
return (NULL);
if ((cur =3D malloc(sizeof(struct pid))) =3D=3D NULL) {
(void)_close(pdes[0]);
(void)_close(pdes[1]);
return (NULL);
}
argv[0] =3D "sh";
argv[1] =3D "-c";
argv[2] =3D (char *)command;
argv[3] =3D NULL;
switch (pid =3D vfork()) {
case -1: /* Error. */
(void)_close(pdes[0]);
(void)_close(pdes[1]);
free(cur);
return (NULL);
/* NOTREACHED */
case 0: /* Child. */
if (*type =3D=3D 'r') {
/*
* The dup2() to STDIN_FILENO is repeated to avoid
* writing to pdes[1], which might corrupt the
* parent's copy. This isn't good enough in
* general, since the _exit() is no return, so
* the compiler is free to corrupt all the local
* variables.
*/
(void)_close(pdes[0]);
if (pdes[1] !=3D STDOUT_FILENO) {
(void)dup2(pdes[1], STDOUT_FILENO);
(void)_close(pdes[1]);
if (twoway)
(void)dup2(STDOUT_FILENO, STDIN_FIL=
ENO);
} else if (twoway && (pdes[1] !=3D STDIN_FILENO))
(void)dup2(pdes[1], STDIN_FILENO);
} else {
if (pdes[0] !=3D STDIN_FILENO) {
(void)dup2(pdes[0], STDIN_FILENO);
(void)_close(pdes[0]);
}
(void)_close(pdes[1]);
}
for (p =3D pidlist; p; p =3D p->next) {
(void)_close(fileno(p->fp));
}
execve(_PATH_BSHELL, argv, environ);
_exit(127);
/* NOTREACHED */
}
---
----
}
--------------------------------------------------
We had cases where our RAID applications (multi-threaded ) failed=20
with invocations of popen() . Initially we handpicked the popen()
calls and replaced it with actual code of the functions but it was
simply too much work and little gain .
So we decided to backport a thread-safe version . (If the above code
is not thread-safe then we will have a bigger problem at hand .)
--Dip
On 7/5/05, Dan Nelson <dnelson@allantgroup.com> wrote:
> In the last episode (Jul 05), Dipjyoti Saikia said:
> > I am working on an OS derived for BSD 4.1 . I am trying to backport
> > a thread-safe version of popen() from BSD 4.10 .
>=20
> popen should be threadsafe as of rev 1.17 (2003-01-03) of
> /usr/src/lib/libc/gen/popen.c . It was merged into the 4.* branch in
> rev 1.14.2.1 (2004/12/15). The PR is bin/50770 . Do you have a
> testcase that causes it to fail?
>=20
> --
> Dan Nelson
> dnelson@allantgroup.com
>
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