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, 17 insertions, 21 deletions

diff --git a/udev_device.c b/udev_device.c
index 4cd5526dea..24f65ca045 100644
--- a/udev_device.c
+++ b/udev_device.c
@@ -173,28 +173,19 @@ int udev_device_event(struct udev_rules *rules, struct udevice *udev)
 			}
 		}
 
-		/* create node and symlinks */
-		retval = udev_node_add(udev, udev_old);
-		if (retval == 0)
-			udev_db_add_device(udev);
+		/* create node */
+		retval = udev_node_add(udev);
+		if (retval != 0)
+			goto exit;
 
-		/* 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);
+		/* store in database */
+		udev_db_add_device(udev);
+
+		/* create, replace, delete symlinks according to priority */
+		udev_node_update_symlinks(udev, udev_old);
+
+		if (udev_old != NULL)
 			udev_device_cleanup(udev_old);
-		}
 		goto exit;
 	}
 
@@ -251,7 +242,8 @@ int udev_device_event(struct udev_rules *rules, struct udevice *udev)
 			list_for_each_entry(name_loop, &udev->env_list, node)
 				putenv(name_loop->name);
 		} else {
-			dbg("'%s' not found in database, using kernel name '%s'", udev->dev->devpath, udev->dev->kernel);
+			dbg("'%s' not found in database, using kernel name '%s'",
+			    udev->dev->devpath, udev->dev->kernel);
 			strlcpy(udev->name, udev->dev->kernel, sizeof(udev->name));
 		}
 
@@ -261,7 +253,11 @@ int udev_device_event(struct udev_rules *rules, struct udevice *udev)
 			goto exit;
 		}
 
+		/* remove the node */
 		retval = udev_node_remove(udev);
+
+		/* delete or restore symlinks according to priority */
+		udev_node_update_symlinks(udev, NULL);
 		goto exit;
 	}