Attached are two files -
cwp.c - implements clone_with_pids() library interface
cwp-test.c - a simple program to test the interface
There maybe more optimal ways of implementing it though :-)
If it makes sense, will submit as a patch to user-cr tree.
Sukadev
/*
* Copied from
*
* http://lkml.indiana.edu/hypermail/linux/kernel/0104.3/0322.html
*
* and hacked to suit clone_with_pids() (Sukadev Bhattiprolu)
*/
/*
* Implementation of Dijkstra's parbegin/parend using clone()
* Modified from original Linus' clone.c example
* A proof of concept for academic purposes
* (c) Francesc Oller 2001, Linus Torvalds
* Under GPL license
*/
#include <unistd.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sched.h>
#include <errno.h>
#define STACKSIZE 8192
#define __NR_clone_with_pids 335
pid_t clone_with_pids(int clone_flags, long *ptid, long *ctid, void *setp)
{
long retval;
long *childsp;
register long * motherbp __asm__ ("%ebp");
/*
* allocate new stack for child
*/
childsp = malloc(STACKSIZE);
if (!childsp)
return -1;
childsp = (long *)(((char *)childsp) + STACKSIZE);
*--childsp = *(motherbp + 1); /* push return address */
*--childsp = *motherbp; /* push mother's bp */
/*
* Do clone() system call. We need to do the low-level stuff
* entirely in assembly as we're returning with a different
* stack in the child process and we couldn't otherwise guarantee
* that the program doesn't use the old stack incorrectly.
*
* Parameters to clone() system call:
* %eax - __NR_clone, clone system call number
* %ebx - clone_flags, bitmap of cloned data
* %ecx - new stack pointer for cloned child
*
* In this example %ebx is CLONE_VM | CLONE_FS | CLONE_FILES |
* CLONE_SIGHAND which shares as much as possible between parent
* and child. (We or in the signal to be sent on child termination
* into clone_flags: SIGCHLD makes the cloned process work like
* a "normal" unix child process)
*
* The clone() system call returns (in %eax) the pid of the newly
* cloned process to the mother, and 0 to the cloned process. If
* an error occurs, the return value will be the negative errno.
*
* Prior to the creation of the child process, we have stored
* return adress and caller's bp in child's stack. Child will
* restore caller's bp and jmp to the post-clone adress. The
* "_exit()" system call at the child's body end will terminate
* the child.
*/
/*
* The last (sixth) parameter goes into ebp but ebp is needed to
* reference local variables. So push values from local variables
* into registers before pushing the pid_set into ebp
*/
__asm__ (
"mov %0, %%ebx"
:
: "r" (clone_flags)
);
__asm__ (
"mov %0, %%ecx"
:
: "r" (childsp)
);
__asm__ (
"mov %0, %%edx"
:
: "r" (&ptid)
);
__asm__ (
"mov %0, %%edi"
:
: "r" (&ctid)
);
__asm__ (
"mov %0, %%ebp"
:
: "r" (setp)
);
__asm__ __volatile__(
"int $0x80\n\t" /* Linux/i386 system call */
"testl %0,%0\n\t" /* check return value */
"jne 1f\n\t" /* jump if mother */
"popl %%ebp\n\t" /* restore caller's bp */
"ret\n" /* jmp to return address */
"1:\t"
:"=a" (retval)
:"0" (__NR_clone_with_pids)
: "%ebx", "%ecx", "%edx", "%edi", "%ebp"
);
if (retval < 0) {
errno = -retval;
retval = -1;
}
return retval;
}
#include <stdio.h>
#include <sched.h>
#include <signal.h>
#include <unistd.h>
#include <errno.h>
#define CLONE_NEWPID 0x20000000
#define __NR_gettid 224
/*
* TODO: getpid() in child returns pid of parent for some reason gettid()
* returns correct pid (i.e 1 if CLONE_NEWPID or 19799 otherwise)
*/
int gettid()
{
int rc;
rc = syscall(__NR_gettid, 0, 0, 0);
if (rc < 0) {
printf("rc %d, errno %d\n", rc, errno);
fflush(stdout);
}
return rc;
}
struct target_pid_set {
int num_pids;
pid_t *target_pids;
};
extern clone_with_pids(int clone_flags, int *ptid, int *ctid, void *pid_set);
main()
{
int rc;
int clone_flags;
struct target_pid_set pid_set;
int pids[1] = { 19799 };
pid_set.num_pids = 1;
pid_set.target_pids = &pids[0];
clone_flags = (CLONE_NEWPID| CLONE_FS | CLONE_FILES | SIGCHLD);
printf("Parent: Call clone_with_pids() for &pid_set %p\n", &pid_set);
rc = clone_with_pids(clone_flags, NULL, NULL, &pid_set);
if (rc == 0) {
printf("Child: tid %d\n", gettid());
_exit(0);
} else if (rc > 0) {
printf("Parent: child pid %d\n", rc);
_exit(0);
} else {
printf("myclone() failed, rc %d, errno %d\n", rc, errno);
}
}
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