don't remove symlinks if they are already there

Consecutive "add" events will not remove and recreate the same symlinks
anymore. No longer valid links, like after changing a filesystem label,
will still be removed.

3 files changed, 61 insertions, 14 deletions

diff --git a/test/udev-test.pl b/test/udev-test.pl
index 33da68a3..fafaa96a 100755
--- a/test/udev-test.pl
+++ b/test/udev-test.pl
@@ -862,6 +862,7 @@ EOF
 		devpath		=> "/class/tty/tty0",
 		exp_name	=> "link",
 		exp_target	=> "link",
+		exp_add_error	=> "yes",
 		exp_rem_error	=> "yes",
 		option		=> "clean",
 		rules		=> <<EOF
diff --git a/udev_device.c b/udev_device.c
index 6dc843ed..a7a8b13c 100644
--- a/udev_device.c
+++ b/udev_device.c
@@ -132,17 +132,38 @@ int udev_device_event(struct udev_rules *rules, struct udevice *udev)
 		/* read current database entry, we may want to cleanup symlinks */
 		udev_old = udev_device_init();
 		if (udev_old != NULL) {
-			if (udev_db_get_device(udev_old, udev->dev->devpath) == 0) {
-				info("device '%s' already known, remove possible symlinks", udev->dev->devpath);
-				udev_node_remove_symlinks(udev_old);
-			}
-			udev_device_cleanup(udev_old);
+			if (udev_db_get_device(udev_old, udev->dev->devpath) != 0) {
+				udev_device_cleanup(udev_old);
+				udev_old = NULL;
+			} else
+				info("device '%s' already in database, validate currently present symlinks",
+				     udev->dev->devpath);
 		}
 
-		/* create node and symlinks, store record in database */
+		/* create node and symlinks */
 		retval = udev_node_add(udev, udev_old);
-		if (retval == 0)
+		if (retval == 0) {
+			/* store record in database */
 			udev_db_add_device(udev);
+
+			/* remove possibly left-over symlinks */
+			if (udev_old != NULL) {
+				struct name_entry *link_loop;
+				struct name_entry *link_old_loop;
+				struct name_entry *link_old_tmp_loop;
+
+				/* remove still valid symlinks from old list */
+				list_for_each_entry_safe(link_old_loop, link_old_tmp_loop, &udev_old->symlink_list, node)
+					list_for_each_entry(link_loop, &udev->symlink_list, node)
+						if (strcmp(link_old_loop->name, link_loop->name) == 0) {
+							dbg("symlink '%s' still valid, keep it", link_old_loop->name);
+							list_del(&link_old_loop->node);
+							free(link_old_loop);
+						}
+				udev_node_remove_symlinks(udev_old);
+				udev_device_cleanup(udev_old);
+			}
+		}
 		goto exit;
 	}
 
diff --git a/udev_node.c b/udev_node.c
index 2a30fe32..ee59d4ae 100644
--- a/udev_node.c
+++ b/udev_node.c
@@ -90,6 +90,36 @@ exit:
 	return retval;
 }
 
+static int udev_node_symlink(struct udevice *udev, const char *linktarget, const char *filename)
+{
+	char target[PATH_SIZE];
+	int len;
+
+	/* look if symlink already exists */
+	len = readlink(filename, target, sizeof(target));
+	if (len > 0) {
+		target[len] = '\0';
+		if (strcmp(linktarget, target) == 0) {
+			info("preserving symlink '%s' to '%s'", filename, linktarget);
+			selinux_setfilecon(filename, NULL, S_IFLNK);
+			goto exit;
+		} else {
+			info("link '%s' points to different target '%s', delete it", filename, target);
+			unlink(filename);
+		}
+	}
+
+	/* create link */
+	info("creating symlink '%s' to '%s'", filename, linktarget);
+	selinux_setfscreatecon(filename, NULL, S_IFLNK);
+	if (symlink(linktarget, filename) != 0)
+		err("symlink(%s, %s) failed: %s", linktarget, filename, strerror(errno));
+	selinux_resetfscreatecon();
+
+exit:
+	return 0;
+}
+
 int udev_node_add(struct udevice *udev, struct udevice *udev_old)
 {
 	char filename[PATH_SIZE];
@@ -205,13 +235,8 @@ int udev_node_add(struct udevice *udev, struct udevice *udev_old)
 			strlcat(linktarget, &udev->name[tail], sizeof(linktarget));
 
 			info("creating symlink '%s' to '%s'", filename, linktarget);
-			if (!udev->test_run) {
-				unlink(filename);
-				selinux_setfscreatecon(filename, NULL, S_IFLNK);
-				if (symlink(linktarget, filename) != 0)
-					err("symlink(%s, %s) failed: %s", linktarget, filename, strerror(errno));
-				selinux_resetfscreatecon();
-			}
+			if (!udev->test_run)
+				udev_node_symlink(udev, linktarget, filename);
 
 			strlcat(symlinks, filename, sizeof(symlinks));
 			strlcat(symlinks, " ", sizeof(symlinks));