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/* mnexec: execution utility for mininet
*
* Starts up programs and does things that are slow or
* difficult in Python, including:
*
* - closing all file descriptors except stdin/out/error
* - detaching from a controlling tty using setsid
* - running in network and mount namespaces
* - printing out the pid of a process so we can identify it later
* - attaching to a namespace and cgroup
* - setting RT scheduling
*
* Partially based on public domain setsid(1)
*/
#define _GNU_SOURCE
#include <stdio.h>
#include <linux/sched.h>
#include <unistd.h>
#include <limits.h>
#include <syscall.h>
#include <fcntl.h>
#include <stdlib.h>
#include <sched.h>
#include <ctype.h>
#include <sys/mount.h>
#if !defined(VERSION)
#define VERSION "(devel)"
#endif
void usage(char *name)
{
printf("Execution utility for Mininet\n\n"
"Usage: %s [-cdnp] [-a pid] [-g group] [-r rtprio] cmd args...\n\n"
"Options:\n"
" -c: close all file descriptors except stdin/out/error\n"
" -d: detach from tty by calling setsid()\n"
" -n: run in new network and mount namespaces\n"
" -p: print ^A + pid\n"
" -a pid: attach to pid's network and mount namespaces\n"
" -g group: add to cgroup\n"
" -r rtprio: run with SCHED_RR (usually requires -g)\n"
" -v: print version\n",
name);
}
int setns(int fd, int nstype)
{
return syscall(__NR_setns, fd, nstype);
}
/* Validate alphanumeric path foo1/bar2/baz */
void validate(char *path)
{
char *s;
for (s=path; *s; s++) {
if (!isalnum(*s) && *s != '/') {
fprintf(stderr, "invalid path: %s\n", path);
exit(1);
}
}
}
/* Add our pid to cgroup */
void cgroup(char *gname)
{
static char path[PATH_MAX];
static char *groups[] = {
"cpu", "cpuacct", "cpuset", NULL
};
char **gptr;
pid_t pid = getpid();
int count = 0;
validate(gname);
for (gptr = groups; *gptr; gptr++) {
FILE *f;
snprintf(path, PATH_MAX, "/sys/fs/cgroup/%s/%s/tasks",
*gptr, gname);
f = fopen(path, "w");
if (f) {
count++;
fprintf(f, "%d\n", pid);
fclose(f);
}
}
if (!count) {
fprintf(stderr, "cgroup: could not add to cgroup %s\n",
gname);
exit(1);
}
}
int main(int argc, char *argv[])
{
int c;
int fd;
char path[PATH_MAX];
int nsid;
int pid;
char *cwd = get_current_dir_name();
static struct sched_param sp;
while ((c = getopt(argc, argv, "+cdnpa:g:r:vh")) != -1)
switch(c) {
case 'c':
/* close file descriptors except stdin/out/error */
for (fd = getdtablesize(); fd > 2; fd--)
close(fd);
break;
case 'd':
/* detach from tty */
if (getpgrp() == getpid()) {
switch(fork()) {
case -1:
perror("fork");
return 1;
case 0: /* child */
break;
default: /* parent */
return 0;
}
}
setsid();
break;
case 'n':
/* run in network and mount namespaces */
if (unshare(CLONE_NEWNET|CLONE_NEWNS) == -1) {
perror("unshare");
return 1;
}
/* Mark our whole hierarchy recursively as private, so that our
* mounts do not propagate to other processes.
*/
if (mount("none", "/", NULL, MS_REC|MS_PRIVATE, NULL) == -1) {
perror("remount");
return 1;
}
/* mount sysfs to pick up the new network namespace */
if (mount("sysfs", "/sys", "sysfs", MS_MGC_VAL, NULL) == -1) {
perror("mount");
return 1;
}
break;
case 'p':
/* print pid */
printf("\001%d\n", getpid());
fflush(stdout);
break;
case 'a':
/* Attach to pid's network namespace and mount namespace */
pid = atoi(optarg);
sprintf(path, "/proc/%d/ns/net", pid);
nsid = open(path, O_RDONLY);
if (nsid < 0) {
perror(path);
return 1;
}
if (setns(nsid, 0) != 0) {
perror("setns");
return 1;
}
/* Plan A: call setns() to attach to mount namespace */
sprintf(path, "/proc/%d/ns/mnt", pid);
nsid = open(path, O_RDONLY);
if (nsid < 0 || setns(nsid, 0) != 0) {
/* Plan B: chroot/chdir into pid's root file system */
sprintf(path, "/proc/%d/root", pid);
if (chroot(path) < 0) {
perror(path);
return 1;
}
}
/* chdir to correct working directory */
if (chdir(cwd) != 0) {
perror(cwd);
return 1;
}
break;
case 'g':
/* Attach to cgroup */
cgroup(optarg);
break;
case 'r':
/* Set RT scheduling priority */
sp.sched_priority = atoi(optarg);
if (sched_setscheduler(getpid(), SCHED_RR, &sp) < 0) {
perror("sched_setscheduler");
return 1;
}
break;
case 'v':
printf("%s\n", VERSION);
exit(0);
case 'h':
usage(argv[0]);
exit(0);
default:
usage(argv[0]);
exit(1);
}
if (optind < argc) {
execvp(argv[optind], &argv[optind]);
perror(argv[optind]);
return 1;
}
usage(argv[0]);
return 0;
}