Date: Mon, 30 Jul 2012 12:24:08 +0200 From: Jilles Tjoelker <jilles@stack.nl> To: freebsd-hackers@freebsd.org Subject: system() using vfork() or posix_spawn() Message-ID: <20120730102408.GA19983@stack.nl>
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People sometimes use system() from large address spaces where it would
improve performance greatly to use vfork() instead of fork().
A simple approach is to change fork() to vfork(), although I have not
tried this. It seems safe enough to use sigaction and sigprocmask system
calls in the vforked process.
Alternatively, we can have posix_spawn() do the vfork() with signal
changes. This avoids possible whining from compilers and static
analyzers about using vfork() in system.c. However, I do not like the
tricky code for signals and that it adds lines of code.
This is lightly tested.
Index: lib/libc/stdlib/system.c
===================================================================
--- lib/libc/stdlib/system.c (revision 238371)
+++ lib/libc/stdlib/system.c (working copy)
@@ -42,16 +42,21 @@
#include <unistd.h>
#include <paths.h>
#include <errno.h>
+#include <spawn.h>
#include "un-namespace.h"
#include "libc_private.h"
+extern char **environ;
+
int
__system(const char *command)
{
pid_t pid, savedpid;
- int pstat;
+ int error, pstat;
struct sigaction ign, intact, quitact;
- sigset_t newsigblock, oldsigblock;
+ sigset_t newsigblock, oldsigblock, defmask;
+ const char *argv[4];
+ posix_spawnattr_t attr;
if (!command) /* just checking... */
return(1);
@@ -65,28 +70,36 @@
ign.sa_flags = 0;
(void)_sigaction(SIGINT, &ign, &intact);
(void)_sigaction(SIGQUIT, &ign, &quitact);
+ (void)sigemptyset(&defmask);
+ if ((intact.sa_flags & SA_SIGINFO) != 0 ||
+ intact.sa_handler != SIG_IGN)
+ (void)sigaddset(&defmask, SIGINT);
+ if ((quitact.sa_flags & SA_SIGINFO) != 0 ||
+ quitact.sa_handler != SIG_IGN)
+ (void)sigaddset(&defmask, SIGQUIT);
(void)sigemptyset(&newsigblock);
(void)sigaddset(&newsigblock, SIGCHLD);
(void)_sigprocmask(SIG_BLOCK, &newsigblock, &oldsigblock);
- switch(pid = fork()) {
- case -1: /* error */
- break;
- case 0: /* child */
- /*
- * Restore original signal dispositions and exec the command.
- */
- (void)_sigaction(SIGINT, &intact, NULL);
- (void)_sigaction(SIGQUIT, &quitact, NULL);
- (void)_sigprocmask(SIG_SETMASK, &oldsigblock, NULL);
- execl(_PATH_BSHELL, "sh", "-c", command, (char *)NULL);
- _exit(127);
- default: /* parent */
+ argv[0] = "sh";
+ argv[1] = "-c";
+ argv[2] = command;
+ argv[3] = NULL;
+ if ((error = posix_spawnattr_init(&attr)) != 0 ||
+ (error = posix_spawnattr_setsigmask(&attr, &oldsigblock)) != 0 ||
+ (error = posix_spawnattr_setsigdefault(&attr, &defmask)) != 0 ||
+ (error = posix_spawnattr_setflags(&attr,
+ POSIX_SPAWN_SETSIGDEF | POSIX_SPAWN_SETSIGMASK)) != 0 ||
+ (error = posix_spawn(&pid, _PATH_BSHELL, NULL, &attr,
+ __DECONST(char **, argv), environ)) != 0) {
+ pid = -1;
+ errno = error;
+ } else {
savedpid = pid;
do {
pid = _wait4(savedpid, &pstat, 0, (struct rusage *)0);
} while (pid == -1 && errno == EINTR);
- break;
}
+ posix_spawnattr_destroy(&attr);
(void)_sigaction(SIGINT, &intact, NULL);
(void)_sigaction(SIGQUIT, &quitact, NULL);
(void)_sigprocmask(SIG_SETMASK, &oldsigblock, NULL);
--
Jilles Tjoelker
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