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.

NEWS

@@ -1,5 +1,7 @@
 udev 138
 ========
+Device nodes can be watched for changes with inotify with OPTIONS="watch".  If
+closed after being opened for writing, a "change" uevent will occur.
 
 udev 137
 ========

udev/Makefile.am

@@ -16,6 +16,7 @@ common_files = \
 	udev.h \
 	udev-sysdeps.h \
 	udev-event.c \
+	udev-watch.c \
 	udev-node.c \
 	udev-rules.c \
 	udev-util.c \

udev/udev-event.c

@@ -600,6 +600,14 @@ int udev_event_execute_rules(struct udev_event *event, struct udev_rules *rules)
 
 		/* create new node and symlinks */
 		err = udev_node_add(dev, event->mode, event->uid, event->gid);
+
+		/* watch for changes */
+		if (event->inotify_watch && inotify_fd != -1) {
+			info(event->udev, "device will be watched for changes\n");
+			udev_watch_begin(event->udev, event->dev);
+		} else {
+			udev_watch_clear(event->udev, event->dev);
+		}
 		goto exit;
 	}
 

udev/udev-rules.c

@@ -140,6 +140,7 @@ enum token_type {
 	TK_A_IGNORE_DEVICE,
 	TK_A_STRING_ESCAPE_NONE,
 	TK_A_STRING_ESCAPE_REPLACE,
+	TK_A_INOTIFY_WATCH,
 	TK_A_NUM_FAKE_PART,		/* int */
 	TK_A_DEVLINK_PRIO,		/* int */
 	TK_A_OWNER,			/* val */
@@ -270,6 +271,7 @@ static const char *token_str(enum token_type type)
 		[TK_A_IGNORE_DEVICE] =		"A IGNORE_DEVICE",
 		[TK_A_STRING_ESCAPE_NONE] =	"A STRING_ESCAPE_NONE",
 		[TK_A_STRING_ESCAPE_REPLACE] =	"A STRING_ESCAPE_REPLACE",
+		[TK_A_INOTIFY_WATCH] = 		"A INOTIFY_WATCH",
 		[TK_A_NUM_FAKE_PART] =		"A NUM_FAKE_PART",
 		[TK_A_DEVLINK_PRIO] =		"A DEVLINK_PRIO",
 		[TK_A_OWNER] =			"A OWNER",
@@ -352,6 +354,7 @@ static void dump_token(struct udev_rules *rules, struct token *token)
 	case TK_A_IGNORE_DEVICE:
 	case TK_A_STRING_ESCAPE_NONE:
 	case TK_A_STRING_ESCAPE_REPLACE:
+	case TK_A_INOTIFY_WATCH:
 	case TK_A_LAST_RULE:
 	case TK_A_IGNORE_REMOVE:
 		dbg(rules->udev, "%s\n", token_str(type));
@@ -1020,6 +1023,7 @@ static int rule_add_key(struct rule_tmp *rule_tmp, enum token_type type,
 	case TK_A_IGNORE_DEVICE:
 	case TK_A_STRING_ESCAPE_NONE:
 	case TK_A_STRING_ESCAPE_REPLACE:
+	case TK_A_INOTIFY_WATCH:
 	case TK_A_IGNORE_REMOVE:
 	case TK_A_LAST_RULE:
 		break;
@@ -1512,6 +1516,11 @@ static int add_rule(struct udev_rules *rules, char *line,
 				rule_add_key(&rule_tmp, TK_A_NUM_FAKE_PART, 0, NULL, &num);
 				dbg(rules->udev, "creation of partition nodes requested\n");
 			}
+			pos = strstr(value, "watch");
+			if (pos != NULL) {
+				rule_add_key(&rule_tmp, TK_A_INOTIFY_WATCH, 0, NULL, NULL);
+				dbg(rules->udev, "inotify watch of device requested\n");
+			}
 			continue;
 		}
 		err(rules->udev, "unknown key '%s' in %s:%u\n", key, filename, lineno);
@@ -2244,6 +2253,9 @@ int udev_rules_apply_to_event(struct udev_rules *rules, struct udev_event *event
 				break;
 			udev_device_set_num_fake_partitions(event->dev, cur->key.num_fake_part);
 			break;
+		case TK_A_INOTIFY_WATCH:
+			event->inotify_watch = 1;
+			break;
 		case TK_A_DEVLINK_PRIO:
 			udev_device_set_devlink_priority(event->dev, cur->key.devlink_prio);
 			break;

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;
+}

udev/udev.h

@@ -75,9 +75,16 @@ struct udev_event {
 	unsigned int devlink_final:1;
 	unsigned int run_final:1;
 	unsigned int ignore_device:1;
+	unsigned int inotify_watch:1;
 	unsigned int trace:1;
 };
 
+struct udev_watch {
+	struct udev_list_node node;
+	int handle;
+	char *name;
+};
+
 /* udev-rules.c */
 struct udev_rules;
 extern struct udev_rules *udev_rules_new(struct udev *udev, int resolve_names);
@@ -93,6 +100,15 @@ extern void udev_event_apply_format(struct udev_event *event, char *string, size
 extern int udev_event_apply_subsys_kernel(struct udev_event *event, const char *string,
 					  char *result, size_t maxsize, int read_value);
 
+/* udev-watch.c */
+extern int inotify_fd;
+extern void udev_watch_init(struct udev *udev);
+extern void udev_watch_restore(struct udev *udev);
+extern void udev_watch_begin(struct udev *udev, struct udev_device *dev);
+extern void udev_watch_clear(struct udev *udev, struct udev_device *dev);
+extern void udev_watch_end(struct udev *udev, int wd);
+extern const char *udev_watch_lookup(struct udev *udev, int wd);
+
 /* udev-node.c */
 extern int udev_node_mknod(struct udev_device *dev, const char *file, dev_t devnum, mode_t mode, uid_t uid, gid_t gid);
 extern int udev_node_add(struct udev_device *dev, mode_t mode, uid_t uid, gid_t gid);

udev/udev.xml

@@ -457,6 +457,13 @@
                       with this option.</para>
                     </listitem>
                   </varlistentry>
+                  <varlistentry>
+                    <term><option>watch</option></term>
+                    <listitem>
+                      <para>Watch the device node with inotify, when closed after being opened for
+		      writing, a change uevent will be synthesised.</para>
+                    </listitem>
+                  </varlistentry>
                 </variablelist>
               </listitem>
             </varlistentry>

udev/udevd.c

@@ -65,7 +65,6 @@ static int debug_trace;
 static struct udev_rules *rules;
 static struct udev_ctrl *udev_ctrl;
 static struct udev_monitor *kernel_monitor;
-static int inotify_fd = -1;
 static volatile int sigchilds_waiting;
 static volatile int udev_exit;
 static volatile int reload_config;
@@ -195,8 +194,6 @@ static void event_fork(struct udev_event *event)
 		/* child */
 		udev_monitor_unref(kernel_monitor);
 		udev_ctrl_unref(udev_ctrl);
-		if (inotify_fd >= 0)
-			close(inotify_fd);
 		logging_close();
 		logging_init("udevd-event");
 		setpriority(PRIO_PROCESS, 0, UDEV_PRIORITY);
@@ -513,6 +510,58 @@ static void handle_ctrl_msg(struct udev_ctrl *uctrl)
 	udev_ctrl_msg_unref(ctrl_msg);
 }
 
+/* read inotify messages */
+static int handle_inotify(struct udev *udev)
+{
+	int nbytes, pos;
+	char *buf;
+	struct inotify_event *ev;
+	int reload_config = 0;
+
+	if ((ioctl(inotify_fd, FIONREAD, &nbytes) < 0) || (nbytes <= 0))
+		return 0;
+
+	buf = malloc(nbytes);
+	if (buf == NULL) {
+		err(udev, "error getting buffer for inotify, disable watching\n");
+		close(inotify_fd);
+		inotify_fd = -1;
+		return 0;
+	}
+
+	read(inotify_fd, buf, nbytes);
+
+	for (pos = 0, ev = (struct inotify_event *)(buf + pos); pos < nbytes; pos += sizeof(struct inotify_event) + ev->len) {
+		const char *syspath;
+
+		dbg(udev, "inotify event: %x for %d (%s)\n", ev->mask, ev->wd, ev->len ? ev->name : "*");
+
+		syspath = udev_watch_lookup(udev, ev->wd);
+		if (syspath != NULL) {
+			dbg(udev, "inotify event: %x for %s\n", ev->mask, syspath);
+			if (ev->mask & IN_CLOSE_WRITE) {
+				char filename[UTIL_PATH_SIZE];
+				int fd;
+
+				info(udev, "device %s closed, synthesising write\n", syspath);
+				util_strlcpy(filename, syspath, sizeof(filename));
+				util_strlcat(filename, "/uevent", sizeof(filename));
+				fd = open(filename, O_WRONLY);
+				if (fd < 0 || write(fd, "change", 6) < 0)
+					info(udev, "error writing uevent: %m\n");
+				close(fd);
+			}
+			if (ev->mask & IN_IGNORED)
+				udev_watch_end(udev, ev->wd);
+		} else {
+			reload_config = 1;
+		}
+	}
+
+	free (buf);
+	return reload_config;
+}
+
 static void asmlinkage sig_handler(int signum)
 {
 	switch (signum) {
@@ -838,7 +887,7 @@ int main(int argc, char *argv[])
 	sigaction(SIGHUP, &act, NULL);
 
 	/* watch rules directory */
-	inotify_fd = inotify_init();
+	udev_watch_init(udev);
 	if (inotify_fd >= 0) {
 		if (udev_get_rules_path(udev) != NULL) {
 			inotify_add_watch(inotify_fd, udev_get_rules_path(udev),
@@ -857,10 +906,9 @@ int main(int argc, char *argv[])
 			inotify_add_watch(inotify_fd, filename,
 					  IN_CREATE | IN_DELETE | IN_MOVE | IN_CLOSE_WRITE);
 		}
-	} 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");
+
+		udev_watch_restore(udev);
+	}
 
 	/* in trace mode run one event after the other */
 	if (debug_trace) {
@@ -936,24 +984,8 @@ int main(int argc, char *argv[])
 		}
 
 		/* rules directory inotify watch */
-		if (inotify_poll && (inotify_poll->revents & POLLIN)) {
-			int nbytes;
-
-			/* discard all possible events, we can just reload the config */
-			if ((ioctl(inotify_fd, FIONREAD, &nbytes) == 0) && nbytes > 0) {
-				char *buf;
-
-				reload_config = 1;
-				buf = malloc(nbytes);
-				if (buf == NULL) {
-					err(udev, "error getting buffer for inotify, disable watching\n");
-					close(inotify_fd);
-					inotify_fd = -1;
-				}
-				read(inotify_fd, buf, nbytes);
-				free(buf);
-			}
-		}
+		if (inotify_poll && (inotify_poll->revents & POLLIN))
+			reload_config = handle_inotify(udev);
 
 handle_signals:
 		signal_received = 0;