Initial support for cgroups

Similar to how systemd creates cgroups for all services, for purposes of
tracking, Finit now does the same.  We also mount all available cgroups
in the /sys/fs/cgroup namespace.

This patch adds support for grouping processes in logical cgroups, like
systemd, and an `initctl ps` command to list the hieararchy.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

src/cgroup.c

@@ -0,0 +1,143 @@
+/* Finit control group support functions
+ *
+ * Copyright (c) 2019  Joachim Nilsson <troglobit@gmail.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <errno.h>
+#include <stdio.h>
+#include <string.h>
+#include <lite/lite.h>
+#include <sys/mount.h>
+
+#include "log.h"
+#include "util.h"
+
+static int cg_init = 0;
+
+/*
+ * Called by Finit at early boot to mount initial cgroups
+ */
+void cgroup_init(void)
+{
+	FILE *fp;
+	char buf[80];
+	int opts = MS_NODEV | MS_NOEXEC | MS_NOSUID;
+
+	fp = fopen("/proc/cgroups", "r");
+	if (!fp) {
+		_d("No cgroup support");
+		return;
+	}
+
+	if (mount("none", "/sys/fs/cgroup", "tmpfs", opts, NULL)) {
+		_d("Failed mounting cgroups");
+		goto fail;
+	}
+
+	/* Skip first line, header */
+	fgets(buf, sizeof(buf), fp);
+	while (fgets(buf, sizeof(buf), fp)) {
+		char *cgroup;
+		char rc[80];
+
+		cgroup = strtok(buf, "\t ");
+		if (!cgroup)
+			continue;
+
+		snprintf(rc, sizeof(rc), "/sys/fs/cgroup/%s", cgroup);
+		mkdir(rc, 0755);
+		if (mount("cgroup", rc, "cgroup", opts, cgroup))
+			_d("Failed mounting %s cgroup on %s", cgroup, rc);
+	}
+
+	/* Default cgroups for process monitoring */
+	mkdir("/sys/fs/cgroup/finit", 0755);
+	if (mount("none", "/sys/fs/cgroup/finit", "cgroup", opts, "none,name=finit")) {
+		_pe("Failed mounting Finit cgroup hierarchy");
+		goto fail;
+	}
+
+	/* Set up reaper and enable callbacks */
+	echo("/sys/fs/cgroup/finit/release_agent", 0, "/libexec/finit/cgreaper.sh");
+	echo("/sys/fs/cgroup/finit/notify_on_release", 0, "1");
+
+	/* Default groups, PID 1, services, and user/login processes */
+	mkdir("/sys/fs/cgroup/finit/init", 0755);
+	mkdir("/sys/fs/cgroup/finit/system", 0755);
+	mkdir("/sys/fs/cgroup/finit/user", 0755);
+
+	/* Move ourselves to init */
+	echo("/sys/fs/cgroup/finit/init/cgroup.procs", 0, "1");
+
+	/* We have signal, main screen turn on! */
+	cg_init = 1;
+fail:
+	fclose(fp);
+}
+
+static int move_pid(char *group, char *name, int pid)
+{
+	char path[256];
+
+	snprintf(path, sizeof(path), "/sys/fs/cgroup/%s/%s", group, name);
+	if (mkdir(path, 0755) && errno != EEXIST)
+		return 1;
+
+	strlcat(path, "/cgroup.procs", sizeof(path));
+
+	return echo(path, 0, "%d", pid);
+}
+
+int cgroup_user(char *name)
+{
+	if (!cg_init)
+		return 0;
+
+	return move_pid("finit/user", name, getpid());
+}
+
+int cgroup_service(char *cmd, int pid)
+{
+	char *nm;
+
+	if (!cg_init)
+		return 0;
+
+	if (pid <= 0) {
+		errno = EINVAL;
+		return 1;
+	}
+
+	nm = strrchr(cmd, '/');
+	if (nm)
+		nm++;
+	else
+		nm = cmd;
+
+	return move_pid("finit/system", nm, pid);
+}
+
+/**
+ * Local Variables:
+ *  indent-tabs-mode: t
+ *  c-file-style: "linux"
+ * End:
+ */