perf daemon: Add config file change check

Add support to detect changes to the daemon's config file triggering a
re-read of the configuration when that happens.

Use a inotify file descriptor plugged into the main fdarray object for
polling.

Example:

  # cat ~/.perfconfig
  [daemon]
  base=/opt/perfdata

  [session-cycles]
  run = -m 10M -e cycles --overwrite --switch-output -a

Starting the daemon:

  # perf daemon start

Check sessions:

  # perf daemon
  [772262:daemon] base: /opt/perfdata
  [772263:cycles] perf record -m 10M -e cycles --overwrite --switch-output -a

Change '-m 10M' to '-m 20M', and check daemon log:

  # tail -f /opt/perfdata/output
  [2021-01-02 20:31:41.234045] daemon started (pid 772262)
  [2021-01-02 20:31:41.235072] reconfig: ruining session [cycles:772263]: -m 10M -e cycles --overwrite --switch-output -a
  [2021-01-02 20:32:08.310137] reconfig: session 'cycles' killed
  [2021-01-02 20:32:08.310847] reconfig: ruining session [cycles:772338]: -m 20M -e cycles --overwrite --switch-output -a

And the session list:

  # perf daemon
  [772262:daemon] base: /opt/perfdata
  [772338:cycles] perf record -m 20M -e cycles --overwrite --switch-output -a

Note the changed '-m 20M' option is in place.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexei Budankov <abudankov@huawei.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: https://lore.kernel.org/r/20210208200908.1019149-8-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-daemon.c

@@ -12,6 +12,8 @@
 #include <stdio.h>
 #include <unistd.h>
 #include <errno.h>
+#include <sys/inotify.h>
+#include <libgen.h>
 #include <sys/types.h>
 #include <sys/socket.h>
 #include <sys/un.h>
@@ -75,6 +77,7 @@ struct daemon_session {
 struct daemon {
 	const char		*config;
 	char			*config_real;
+	char			*config_base;
 	const char		*base_user;
 	char			*base;
 	struct list_head	 sessions;
@@ -530,6 +533,7 @@ static void daemon__exit(struct daemon *daemon)
 		daemon_session__remove(session);
 
 	free(daemon->config_real);
+	free(daemon->config_base);
 	free(daemon->base);
 }
 
@@ -566,6 +570,84 @@ static int daemon__reconfig(struct daemon *daemon)
 	return 0;
 }
 
+static int setup_config_changes(struct daemon *daemon)
+{
+	char *basen = strdup(daemon->config_real);
+	char *dirn  = strdup(daemon->config_real);
+	char *base, *dir;
+	int fd, wd = -1;
+
+	if (!dirn || !basen)
+		goto out;
+
+	fd = inotify_init1(IN_NONBLOCK|O_CLOEXEC);
+	if (fd < 0) {
+		perror("failed: inotify_init");
+		goto out;
+	}
+
+	dir = dirname(dirn);
+	base = basename(basen);
+	pr_debug("config file: %s, dir: %s\n", base, dir);
+
+	wd = inotify_add_watch(fd, dir, IN_CLOSE_WRITE);
+	if (wd >= 0) {
+		daemon->config_base = strdup(base);
+		if (!daemon->config_base) {
+			close(fd);
+			wd = -1;
+		}
+	} else {
+		perror("failed: inotify_add_watch");
+	}
+
+out:
+	free(basen);
+	free(dirn);
+	return wd < 0 ? -1 : fd;
+}
+
+static bool process_inotify_event(struct daemon *daemon, char *buf, ssize_t len)
+{
+	char *p = buf;
+
+	while (p < (buf + len)) {
+		struct inotify_event *event = (struct inotify_event *) p;
+
+		/*
+		 * We monitor config directory, check if our
+		 * config file was changes.
+		 */
+		if ((event->mask & IN_CLOSE_WRITE) &&
+		    !(event->mask & IN_ISDIR)) {
+			if (!strcmp(event->name, daemon->config_base))
+				return true;
+		}
+		p += sizeof(*event) + event->len;
+	}
+	return false;
+}
+
+static int handle_config_changes(struct daemon *daemon, int conf_fd,
+				 bool *config_changed)
+{
+	char buf[4096];
+	ssize_t len;
+
+	while (!(*config_changed)) {
+		len = read(conf_fd, buf, sizeof(buf));
+		if (len == -1) {
+			if (errno != EAGAIN) {
+				perror("failed: read");
+				return -1;
+			}
+			return 0;
+		}
+		*config_changed = process_inotify_event(daemon, buf, len);
+	}
+	return 0;
+}
+
 static int setup_config(struct daemon *daemon)
 {
 	if (daemon->base_user) {
@@ -600,8 +682,8 @@ static int __cmd_start(struct daemon *daemon, struct option parent_options[],
 		OPT_PARENT(parent_options),
 		OPT_END()
 	};
-	int sock_fd = -1;
-	int sock_pos;
+	int sock_fd = -1, conf_fd = -1;
+	int sock_pos, file_pos;
 	struct fdarray fda;
 	int err = 0;
 
@@ -622,16 +704,24 @@ static int __cmd_start(struct daemon *daemon, struct option parent_options[],
 
 	pr_info("daemon started (pid %d)\n", getpid());
 
-	fdarray__init(&fda, 1);
+	fdarray__init(&fda, 2);
 
 	sock_fd = setup_server_socket(daemon);
 	if (sock_fd < 0)
 		goto out;
 
+	conf_fd = setup_config_changes(daemon);
+	if (conf_fd < 0)
+		goto out;
+
 	sock_pos = fdarray__add(&fda, sock_fd, POLLIN|POLLERR|POLLHUP, 0);
 	if (sock_pos < 0)
 		goto out;
 
+	file_pos = fdarray__add(&fda, conf_fd, POLLIN|POLLERR|POLLHUP, 0);
+	if (file_pos < 0)
+		goto out;
+
 	signal(SIGINT, sig_handler);
 	signal(SIGTERM, sig_handler);
 
@@ -643,6 +733,8 @@ static int __cmd_start(struct daemon *daemon, struct option parent_options[],
 
 			if (fda.entries[sock_pos].revents & POLLIN)
 				err = handle_server_socket(daemon, sock_fd);
+			if (fda.entries[file_pos].revents & POLLIN)
+				err = handle_config_changes(daemon, conf_fd, &reconfig);
 
 			if (reconfig)
 				err = setup_server_config(daemon);
@@ -657,6 +749,8 @@ out:
 
 	if (sock_fd != -1)
 		close(sock_fd);
+	if (conf_fd != -1)
+		close(conf_fd);
 
 	pr_info("daemon exited\n");
 	fclose(daemon->out);