priority based symlink handling

Symlinks can have priorities now, the priority is assigned to the device
and specified with OPTIONS="link_priority=100". Devices with higher
priorities overwrite the symlinks of devices with lower priorities.
If the device, that currently owns the link goes away, the symlink
will be removed, and recreated, pointing to the next device with the
highest actual priority.

This should solve the issue, that inserting an USB-stick may overwrite the
/dev/disk/by-id/-link of another disk, and removes the entire link after the
USB-stick is disconnected. If no priorities are specified, the new link will
overwrite the current one, and if the device goes away, it will restore
the old link. It should be possible to assign lower priorities to removable
devices, if needed.

In multipath setups, we see several devices, which all connect to the same
volume, and therefore all try to create the same metadata-links. The
different path-devices are combined into one device-mapper device, which also
contains the same metadata. It should be possible, to assign multipath-table
device-mapper devices a higher priority, so path-devices that appear and
disappear, will not overwrite or delete the device-mapper device links.

1 files changed, 133 insertions, 102 deletions

diff --git a/udev_node.c b/udev_node.c
index 1558df849c..526d713516 100644
--- a/udev_node.c
+++ b/udev_node.c
@@ -25,6 +25,7 @@
 #include <unistd.h>
 #include <errno.h>
 #include <grp.h>
+#include <dirent.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 
@@ -114,7 +115,7 @@ static int node_symlink(const char *node, const char *slink)
 	if (len > 0) {
 		buf[len] = '\0';
 		if (strcmp(target, buf) == 0) {
-			info("preserving symlink '%s' to '%s'", slink, target);
+			info("preserve already existing symlink '%s' to '%s'", slink, target);
 			selinux_setfilecon(slink, NULL, S_IFLNK);
 			goto exit;
 		}
@@ -133,7 +134,131 @@ exit:
 	return 0;
 }
 
-int udev_node_add(struct udevice *udev, struct udevice *udev_old)
+static int update_link(struct udevice *udev, const char *name)
+{
+	LIST_HEAD(name_list);
+	char slink[PATH_SIZE];
+	char node[PATH_SIZE];
+	struct udevice *udev_db;
+	struct name_entry *device;
+	char target[PATH_MAX] = "";
+	int count;
+	int priority = 0;
+	int rc = 0;
+
+	strlcpy(slink, udev_root, sizeof(slink));
+	strlcat(slink, "/", sizeof(slink));
+	strlcat(slink, name, sizeof(slink));
+
+	count = udev_db_get_devices_by_name(name, &name_list);
+	info("found %i devices with name '%s'", count, name);
+
+	/* if we don't have any reference, we can delete the link */
+	if (count <= 0) {
+		info("no reference left, remove '%s'", name);
+		if (!udev->test_run) {
+			unlink(slink);
+			delete_path(slink);
+		}
+		goto out;
+	}
+
+	/* find the device with the highest priority */
+	list_for_each_entry(device, &name_list, node) {
+		info("found '%s' for '%s'", device->name, name);
+
+		/* did we find ourself? we win, if we have the same priority */
+		if (strcmp(udev->dev->devpath, device->name) == 0) {
+			info("compare (our own) priority of '%s' %i >= %i",
+			     udev->dev->devpath, udev->link_priority, priority);
+			if (target[0] == '\0' || udev->link_priority >= priority) {
+				priority = udev->link_priority;
+				strlcpy(target, udev->name, sizeof(target));
+			}
+			continue;
+		}
+
+		/* or something else, then read priority from database */
+		udev_db = udev_device_init(NULL);
+		if (udev_db == NULL)
+			continue;
+		if (udev_db_get_device(udev_db, device->name) == 0) {
+			info("compare priority of '%s' %i > %i",
+			     udev_db->dev->devpath, udev_db->link_priority, priority);
+			if (target[0] == '\0' || udev_db->link_priority > priority) {
+				priority = udev_db->link_priority;
+				strlcpy(target, udev_db->name, sizeof(target));
+			}
+		}
+		udev_device_cleanup(udev_db);
+	}
+	name_list_cleanup(&name_list);
+
+	if (target[0] == '\0') {
+		err("missing target for '%s'", name);
+		rc = -1;
+		goto out;
+	}
+
+	/* create symlink to the target with the highest priority */
+	strlcpy(node, udev_root, sizeof(node));
+	strlcat(node, "/", sizeof(node));
+	strlcat(node, target, sizeof(node));
+	info("'%s' with target '%s' has the highest priority %i, create it", name, target, priority);
+	if (!udev->test_run) {
+		create_path(slink);
+		node_symlink(node, slink);
+	}
+out:
+	return rc;
+}
+
+void udev_node_update_symlinks(struct udevice *udev, struct udevice *udev_old)
+{
+	struct name_entry *name_loop;
+	char symlinks[PATH_SIZE] = "";
+
+	list_for_each_entry(name_loop, &udev->symlink_list, node) {
+		info("update symlink '%s' of '%s'", name_loop->name, udev->dev->devpath);
+		update_link(udev, name_loop->name);
+		strlcat(symlinks, udev_root, sizeof(symlinks));
+		strlcat(symlinks, "/", sizeof(symlinks));
+		strlcat(symlinks, name_loop->name, sizeof(symlinks));
+		strlcat(symlinks, " ", sizeof(symlinks));
+	}
+
+	/* export symlinks to environment */
+	remove_trailing_chars(symlinks, ' ');
+	if (symlinks[0] != '\0')
+		setenv("DEVLINKS", symlinks, 1);
+
+	/* update possible left-over symlinks (device metadata changed) */
+	if (udev_old != NULL) {
+		struct name_entry *link_loop;
+		struct name_entry *link_old_loop;
+		struct name_entry *link_old_tmp_loop;
+		int found;
+
+		/* remove current symlinks from old list */
+		list_for_each_entry_safe(link_old_loop, link_old_tmp_loop, &udev_old->symlink_list, node) {
+			found = 0;
+			list_for_each_entry(link_loop, &udev->symlink_list, node) {
+				if (strcmp(link_old_loop->name, link_loop->name) == 0) {
+					found = 1;
+					break;
+				}
+			}
+			if (!found) {
+				/* link does no longer belong to this device */
+				info("update old symlink '%s' no longer belonging to '%s'",
+				     link_old_loop->name, udev->dev->devpath);
+				update_link(udev, link_old_loop->name);
+			}
+		}
+	}
+}
+
+int udev_node_add(struct udevice *udev)
 {
 	char filename[PATH_SIZE];
 	uid_t uid;
@@ -141,10 +266,9 @@ int udev_node_add(struct udevice *udev, struct udevice *udev_old)
 	int i;
 	int retval = 0;
 
-	snprintf(filename, sizeof(filename), "%s/%s", udev_root, udev->name);
-	filename[sizeof(filename)-1] = '\0';
-
-	/* create parent directories if needed */
+	strlcpy(filename, udev_root, sizeof(filename));
+	strlcat(filename, "/", sizeof(filename));
+	strlcat(filename, udev->name, sizeof(filename));
 	create_path(filename);
 
 	if (strcmp(udev->owner, "root") == 0)
@@ -209,102 +333,10 @@ int udev_node_add(struct udevice *udev, struct udevice *udev_old)
 			}
 		}
 	}
-
-	/* create symlink(s) if requested */
-	if (!list_empty(&udev->symlink_list)) {
-		struct name_entry *name_loop;
-		char symlinks[PATH_SIZE] = "";
-
-		list_for_each_entry(name_loop, &udev->symlink_list, node) {
-			char slink[PATH_SIZE];
-
-			strlcpy(slink, udev_root, sizeof(slink));
-			strlcat(slink, "/", sizeof(slink));
-			strlcat(slink, name_loop->name, sizeof(slink));
-
-			info("creating symlink '%s' to node '%s'", slink, filename);
-			if (!udev->test_run) {
-				create_path(slink);
-				node_symlink(filename, slink);
-			}
-
-			strlcat(symlinks, slink, sizeof(symlinks));
-			strlcat(symlinks, " ", sizeof(symlinks));
-		}
-
-		remove_trailing_chars(symlinks, ' ');
-		setenv("DEVLINKS", symlinks, 1);
-	}
-
 exit:
 	return retval;
 }
 
-void udev_node_remove_symlinks(struct udevice *udev)
-{
-	char filename[PATH_SIZE];
-	struct name_entry *name_loop;
-	struct stat stats;
-
-	if (!list_empty(&udev->symlink_list)) {
-		char symlinks[PATH_SIZE] = "";
-
-		list_for_each_entry(name_loop, &udev->symlink_list, node) {
-			char devpath[PATH_SIZE];
-
-			snprintf(filename, sizeof(filename), "%s/%s", udev_root, name_loop->name);
-			filename[sizeof(filename)-1] = '\0';
-
-			if (stat(filename, &stats) != 0) {
-				dbg("symlink '%s' not found", filename);
-				continue;
-			}
-			if (udev->devt && stats.st_rdev != udev->devt) {
-				info("symlink '%s' points to a different device, skip removal", filename);
-				continue;
-			}
-
-			info("removing symlink '%s'", filename);
-			if (!udev->test_run) {
-				unlink(filename);
-				delete_path(filename);
-			}
-
-			/* see if another device wants this symlink */
-			if (udev_db_lookup_name(name_loop->name, devpath, sizeof(devpath)) == 0) {
-				struct udevice *old;
-
-				info("found overwritten symlink '%s' of '%s'", name_loop->name, devpath);
-				old = udev_device_init(NULL);
-				if (old != NULL) {
-					if (udev_db_get_device(old, devpath) == 0) {
-						char slink[PATH_SIZE];
-						char node[PATH_SIZE];
-
-						strlcpy(slink, udev_root, sizeof(slink));
-						strlcat(slink, "/", sizeof(slink));
-						strlcat(slink, name_loop->name, sizeof(slink));
-						strlcpy(node, udev_root, sizeof(node));
-						strlcat(node, "/", sizeof(node));
-						strlcat(node, old->name, sizeof(node));
-						info("restore symlink '%s' to '%s'", slink, node);
-						if (!udev->test_run)
-							node_symlink(node, slink);
-					}
-					udev_device_cleanup(old);
-				}
-			}
-
-			strlcat(symlinks, filename, sizeof(symlinks));
-			strlcat(symlinks, " ", sizeof(symlinks));
-		}
-
-		remove_trailing_chars(symlinks, ' ');
-		if (symlinks[0] != '\0')
-			setenv("DEVLINKS", symlinks, 1);
-	}
-}
-
 int udev_node_remove(struct udevice *udev)
 {
 	char filename[PATH_SIZE];
@@ -313,10 +345,9 @@ int udev_node_remove(struct udevice *udev)
 	int retval;
 	int num;
 
-	udev_node_remove_symlinks(udev);
-
-	snprintf(filename, sizeof(filename), "%s/%s", udev_root, udev->name);
-	filename[sizeof(filename)-1] = '\0';
+	strlcpy(filename, udev_root, sizeof(filename));
+	strlcat(filename, "/", sizeof(filename));
+	strlcat(filename, udev->name, sizeof(filename));
 	if (stat(filename, &stats) != 0) {
 		dbg("device node '%s' not found", filename);
 		return -1;