cgroup_util.c

/* SPDX-License-Identifier: GPL-2.0 */

#define _GNU_SOURCE

#include <errno.h>
#include <fcntl.h>
#include <linux/limits.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>

#include "cgroup_util.h"

static ssize_t read_text(const char *path, char *buf, size_t max_len)
{
	ssize_t len;
	int fd;

	fd = open(path, O_RDONLY);
	if (fd < 0)
		return fd;

	len = read(fd, buf, max_len - 1);
	if (len < 0)
		goto out;

	buf[len] = 0;
out:
	close(fd);
	return len;
}

static ssize_t write_text(const char *path, char *buf, size_t len)
{
	int fd;

	fd = open(path, O_WRONLY | O_APPEND);
	if (fd < 0)
		return fd;

	len = write(fd, buf, len);
	if (len < 0) {
		close(fd);
		return len;
	}

	close(fd);

	return len;
}

char *cg_name(const char *root, const char *name)
{
	size_t len = strlen(root) + strlen(name) + 2;
	char *ret = malloc(len);

	if (name)
		snprintf(ret, len, "%s/%s", root, name);

	return ret;
}

char *cg_name_indexed(const char *root, const char *name, int index)
{
	size_t len = strlen(root) + strlen(name) + 10;
	char *ret = malloc(len);

	if (name)
		snprintf(ret, len, "%s/%s_%d", root, name, index);

	return ret;
}

int cg_read(const char *cgroup, const char *control, char *buf, size_t len)
{
	char path[PATH_MAX];

	snprintf(path, sizeof(path), "%s/%s", cgroup, control);

	if (read_text(path, buf, len) >= 0)
		return 0;

	return -1;
}

int cg_read_strcmp(const char *cgroup, const char *control,
		   const char *expected)
{
	size_t size = strlen(expected) + 1;
	char *buf;

	buf = malloc(size);
	if (!buf)
		return -1;

	if (cg_read(cgroup, control, buf, size))
		return -1;

	return strcmp(expected, buf);
}

int cg_read_strstr(const char *cgroup, const char *control, const char *needle)
{
	char buf[PAGE_SIZE];

	if (cg_read(cgroup, control, buf, sizeof(buf)))
		return -1;

	return strstr(buf, needle) ? 0 : -1;
}

long cg_read_long(const char *cgroup, const char *control)
{
	char buf[128];

	if (cg_read(cgroup, control, buf, sizeof(buf)))
		return -1;

	return atol(buf);
}

long cg_read_key_long(const char *cgroup, const char *control, const char *key)
{
	char buf[PAGE_SIZE];
	char *ptr;

	if (cg_read(cgroup, control, buf, sizeof(buf)))
		return -1;

	ptr = strstr(buf, key);
	if (!ptr)
		return -1;

	return atol(ptr + strlen(key));
}

int cg_write(const char *cgroup, const char *control, char *buf)
{
	char path[PATH_MAX];
	size_t len = strlen(buf);

	snprintf(path, sizeof(path), "%s/%s", cgroup, control);

	if (write_text(path, buf, len) == len)
		return 0;

	return -1;
}

int cg_find_unified_root(char *root, size_t len)
{
	char buf[10 * PAGE_SIZE];
	char *fs, *mount, *type;
	const char delim[] = "\n\t ";

	if (read_text("/proc/self/mounts", buf, sizeof(buf)) <= 0)
		return -1;

	/*
	 * Example:
	 * cgroup /sys/fs/cgroup cgroup2 rw,seclabel,noexec,relatime 0 0
	 */
	for (fs = strtok(buf, delim); fs; fs = strtok(NULL, delim)) {
		mount = strtok(NULL, delim);
		type = strtok(NULL, delim);
		strtok(NULL, delim);
		strtok(NULL, delim);
		strtok(NULL, delim);

		if (strcmp(fs, "cgroup") == 0 &&
		    strcmp(type, "cgroup2") == 0) {
			strncpy(root, mount, len);
			return 0;
		}
	}

	return -1;
}

int cg_create(const char *cgroup)
{
	return mkdir(cgroup, 0644);
}

static int cg_killall(const char *cgroup)
{
	char buf[PAGE_SIZE];
	char *ptr = buf;

	if (cg_read(cgroup, "cgroup.procs", buf, sizeof(buf)))
		return -1;

	while (ptr < buf + sizeof(buf)) {
		int pid = strtol(ptr, &ptr, 10);

		if (pid == 0)
			break;
		if (*ptr)
			ptr++;
		else
			break;
		if (kill(pid, SIGKILL))
			return -1;
	}

	return 0;
}

int cg_destroy(const char *cgroup)
{
	int ret;

retry:
	ret = rmdir(cgroup);
	if (ret && errno == EBUSY) {
		ret = cg_killall(cgroup);
		if (ret)
			return ret;
		usleep(100);
		goto retry;
	}

	if (ret && errno == ENOENT)
		ret = 0;

	return ret;
}

int cg_run(const char *cgroup,
	   int (*fn)(const char *cgroup, void *arg),
	   void *arg)
{
	int pid, retcode;

	pid = fork();
	if (pid < 0) {
		return pid;
	} else if (pid == 0) {
		char buf[64];

		snprintf(buf, sizeof(buf), "%d", getpid());
		if (cg_write(cgroup, "cgroup.procs", buf))
			exit(EXIT_FAILURE);
		exit(fn(cgroup, arg));
	} else {
		waitpid(pid, &retcode, 0);
		if (WIFEXITED(retcode))
			return WEXITSTATUS(retcode);
		else
			return -1;
	}
}

int cg_run_nowait(const char *cgroup,
		  int (*fn)(const char *cgroup, void *arg),
		  void *arg)
{
	int pid;

	pid = fork();
	if (pid == 0) {
		char buf[64];

		snprintf(buf, sizeof(buf), "%d", getpid());
		if (cg_write(cgroup, "cgroup.procs", buf))
			exit(EXIT_FAILURE);
		exit(fn(cgroup, arg));
	}

	return pid;
}

int get_temp_fd(void)
{
	return open(".", O_TMPFILE | O_RDWR | O_EXCL);
}

int alloc_pagecache(int fd, size_t size)
{
	char buf[PAGE_SIZE];
	struct stat st;
	int i;

	if (fstat(fd, &st))
		goto cleanup;

	size += st.st_size;

	if (ftruncate(fd, size))
		goto cleanup;

	for (i = 0; i < size; i += sizeof(buf))
		read(fd, buf, sizeof(buf));

	return 0;

cleanup:
	return -1;
}

int alloc_anon(const char *cgroup, void *arg)
{
	size_t size = (unsigned long)arg;
	char *buf, *ptr;

	buf = malloc(size);
	for (ptr = buf; ptr < buf + size; ptr += PAGE_SIZE)
		*ptr = 0;

	free(buf);
	return 0;
}