udevd: optionally watch device nodes with inotify

This allows you to re-process the rules if the content of the device
has been changed, most useful for block subsystem to cause vol_id to
be run again.

1 files changed, 236 insertions, 0 deletions

diff --git a/udev/udev-watch.c b/udev/udev-watch.c
new file mode 100644
index 0000000000..24df481cf8
--- /dev/null
+++ b/udev/udev-watch.c
@@ -0,0 +1,236 @@
+/*
+ * Copyright (C) 2004-2008 Kay Sievers <kay.sievers@vrfy.org>
+ * Copyright (C) 2009 Canonical Ltd.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <sys/types.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <dirent.h>
+#include <stddef.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#ifdef HAVE_INOTIFY
+#include <sys/inotify.h>
+#endif
+
+#include "udev.h"
+
+int inotify_fd = -1;
+
+/* inotify descriptor, will be shared with rules directory;
+ * set to cloexec since we need our children to be able to add
+ * watches for us
+ */
+void udev_watch_init(struct udev *udev)
+{
+	inotify_fd = inotify_init();
+	if (inotify_fd >= 0) {
+		int flags;
+
+		flags = fcntl(inotify_fd, F_GETFD);
+		if (flags < 0)
+			flags = FD_CLOEXEC;
+		else
+			flags |= FD_CLOEXEC;
+		fcntl(inotify_fd, F_SETFD, flags);
+	} else if (errno == ENOSYS)
+		info(udev, "unable to use inotify, udevd will not monitor rule files changes\n");
+	else
+		err(udev, "inotify_init failed: %m\n");
+}
+
+/* move any old watches directory out of the way, and then restore
+ * the watches
+ */
+void udev_watch_restore(struct udev *udev)
+{
+	char filename[UTIL_PATH_SIZE], oldname[UTIL_PATH_SIZE];
+
+	if (inotify_fd < 0)
+		return;
+
+	util_strlcpy(oldname, udev_get_dev_path(udev), sizeof(oldname));
+	util_strlcat(oldname, "/.udev/watch.old", sizeof(oldname));
+
+	util_strlcpy(filename, udev_get_dev_path(udev), sizeof(filename));
+	util_strlcat(filename, "/.udev/watch", sizeof(filename));
+
+	if (rename(filename, oldname) == 0) {
+		DIR *dir;
+		struct dirent *ent;
+
+		dir = opendir(oldname);
+		if (dir == NULL) {
+			err(udev, "unable to open old watches dir '%s', old watches will not be restored: %m", oldname);
+			return;
+		}
+
+		while ((ent = readdir(dir)) != NULL) {
+			char path[UTIL_PATH_SIZE];
+			char buf[UTIL_PATH_SIZE];
+			ssize_t len;
+			struct udev_device *dev;
+
+			if (ent->d_name[0] < '0' || ent->d_name[0] > '9')
+				continue;
+
+			util_strlcpy(path, oldname, sizeof(path));
+			util_strlcat(path, "/", sizeof(path));
+			util_strlcat(path, ent->d_name, sizeof(path));
+
+			len = readlink(path, buf, sizeof(buf));
+			if (len <= 0) {
+				unlink(path);
+				continue;
+			}
+
+			buf[len] = '\0';
+			dbg(udev, "old watch to '%s' found\n", buf);
+
+			dev = udev_device_new_from_syspath(udev, buf);
+			if (dev == NULL) {
+				unlink(path);
+				continue;
+			}
+
+			udev_device_read_db(dev);
+			udev_device_set_info_loaded(dev);
+
+			info(udev, "restoring old watch on '%s'\n", udev_device_get_devnode(dev));
+			udev_watch_begin(udev, dev);
+
+			udev_device_unref(dev);
+
+			unlink(path);
+		}
+
+		closedir(dir);
+		rmdir(oldname);
+
+	} else if (errno != ENOENT) {
+		err(udev, "unable to move watches dir '%s', old watches will not be restored: %m", filename);
+	}
+}
+
+static const char *udev_watch_filename(struct udev *udev, int wd)
+{
+	static char filename[UTIL_PATH_SIZE];
+	char str[32];
+
+	sprintf(str, "%d", wd);
+	util_strlcpy(filename, udev_get_dev_path(udev), sizeof(filename));
+	util_strlcat(filename, "/.udev/watch/", sizeof(filename));
+	util_strlcat(filename, str, sizeof(filename));
+
+	return filename;
+}
+
+void udev_watch_begin(struct udev *udev, struct udev_device *dev)
+{
+	const char *filename;
+	int wd;
+
+	if (inotify_fd < 0)
+		return;
+
+	wd = inotify_add_watch (inotify_fd, udev_device_get_devnode(dev), IN_CLOSE_WRITE);
+	if (wd < 0) {
+		err(udev, "inotify_add_watch(%d, %s, %o) failed: %m\n",
+		    inotify_fd, udev_device_get_devnode(dev), IN_CLOSE_WRITE);
+	}
+
+	filename = udev_watch_filename(udev, wd);
+	util_create_path(udev, filename);
+	unlink(filename);
+	symlink(udev_device_get_syspath(dev), filename);
+}
+
+void udev_watch_clear(struct udev *udev, struct udev_device *dev)
+{
+	static char filename[UTIL_PATH_SIZE];
+	DIR *dir;
+	struct dirent *ent;
+
+	util_strlcpy(filename, udev_get_dev_path(udev), sizeof(filename));
+	util_strlcat(filename, "/.udev/watch", sizeof(filename));
+
+	dir = opendir(filename);
+	if (dir == NULL)
+		return;
+
+	while ((ent = readdir(dir)) != NULL) {
+		char path[UTIL_PATH_SIZE];
+		char buf[UTIL_PATH_SIZE];
+		ssize_t len;
+
+		if (ent->d_name[0] < '0' || ent->d_name[0] > '9')
+			continue;
+
+		util_strlcpy(path, filename, sizeof(path));
+		util_strlcat(path, "/", sizeof(path));
+		util_strlcat(path, ent->d_name, sizeof(path));
+
+		len = readlink(path, buf, sizeof(buf));
+		if (len <= 0)
+			continue;
+
+		buf[len] = '\0';
+		if (strcmp(buf, udev_device_get_syspath(dev)))
+			continue;
+
+		/* this is the watch we're looking for */
+		info(udev, "clearing existing watch on '%s'\n", udev_device_get_devnode(dev));
+		udev_watch_end(udev, atoi(ent->d_name));
+	}
+
+	closedir(dir);
+}
+
+void udev_watch_end(struct udev *udev, int wd)
+{
+	const char *filename;
+
+	if (inotify_fd < 0 || wd < 0)
+		return;
+
+	inotify_rm_watch(inotify_fd, wd);
+
+	filename = udev_watch_filename(udev, wd);
+	unlink(filename);
+}
+
+const char *udev_watch_lookup(struct udev *udev, int wd)
+{
+	const char *filename;
+	static char buf[UTIL_PATH_SIZE];
+	ssize_t len;
+
+	if (inotify_fd < 0 || wd < 0)
+		return NULL;
+
+	filename = udev_watch_filename(udev, wd);
+	len = readlink(filename, buf, sizeof(buf));
+	if (len > 0) {
+		buf[len] = '\0';
+
+		return buf;
+	}
+
+	return NULL;
+}