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isolate-cg-keeper.c
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isolate-cg-keeper.c
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/*
* A Trivial Helper Daemon for Keeping Control Groups in SystemD
*
* (c) 2022--2023 Martin Mares <mj@ucw.cz>
*/
#include "isolate.h"
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/stat.h>
#include <systemd/sd-daemon.h>
void NONRET __attribute__((format(printf,1,2)))
die(char *msg, ...)
{
va_list args;
va_start(args, msg);
vfprintf(stderr, msg, args);
fputc('\n', stderr);
exit(1);
}
static void __attribute__((format(printf,3,4)))
write_cg_attr(const char *cg_root, const char *name, const char *fmt, ...)
{
va_list args;
va_start(args, fmt);
char namebuf[1024];
snprintf(namebuf, sizeof(namebuf), "%s/%s", cg_root, name);
char valbuf[1024];
vsnprintf(valbuf, sizeof(valbuf), fmt, args);
int len = strlen(valbuf);
int fd = open(namebuf, O_WRONLY);
if (fd < 0)
die("Cannot open %s: %m", namebuf);
if (write(fd, valbuf, len) != len)
die("Cannot write to %s: %m", namebuf);
close(fd);
va_end(args);
}
static char *
get_my_cgroup(void)
{
if (!(strlen(cf_cg_root) > 5 && !memcmp(cf_cg_root, "auto:", 5)))
return cf_cg_root;
FILE *f = fopen("/proc/self/cgroup", "r");
if (!f)
die("Cannot open /proc/self/cgroup: %m");
char *line = NULL;
size_t buflen = 0;
ssize_t len;
char *cg = NULL;
while ((len = getline(&line, &buflen, f)) >= 0)
{
if (len > 0 && line[len-1] == '\n')
line[--len] = 0;
if (line[0] == '0' && line[1] == ':' && line[2] == ':')
{
cg = xsprintf("/sys/fs/cgroup%s", line + 3);
break;
}
}
if (!cg)
die("Cannot find my own cgroup");
free(line);
fclose(f);
return cg;
}
static void
write_auto_cgroup(char *file, char *cg)
{
make_dir_for(file);
FILE *f = fopen(file, "w");
if (!f)
die("Cannot create %s: %m", file);
fprintf(f, "%s\n", cg);
fclose(f);
}
static void
setup_cg(void)
{
char *cg = cf_cg_root;
if (strlen(cf_cg_root) > 5 && !memcmp(cf_cg_root, "auto:", 5))
{
cg = get_my_cgroup();
write_auto_cgroup(cf_cg_root + 5, cg);
}
struct stat st;
if (stat(cg, &st), 0)
die("Control group root %s does not exist: %m", cg);
char subgroup[1024];
snprintf(subgroup, sizeof(subgroup), "%s/daemon", cg);
if (mkdir(subgroup, 0777) < 0)
die("Cannot create subgroup %s: %m", subgroup);
write_cg_attr(cg, "daemon/cgroup.procs", "%d\n", (int) getpid());
write_cg_attr(cg, "cgroup.subtree_control", "+cpuset +memory\n");
}
int
main(int argc UNUSED, char **argv UNUSED)
{
cf_parse();
setup_cg();
sd_notify(0, "READY=1");
for (;;)
pause();
}