From 3bf768245b98479a14190e1e1d32ef5fae3ddf8a Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Mon, 27 Jul 2009 23:24:27 +0200
Subject: [PATCH] enumeration: move ALSA control devices to the end of the
 enumerated devices of each card

Generally ALSA control devices should be the last ones to be processed
for ACL changes and similar operations because they can then be used as
indicators that ACL management finished for all device nodes of a
specific card.

This patch simple moves each controlC device behind all the pcmC devices
(and similar).
---
 libudev/libudev-enumerate.c | 59 +++++++++++++++++++++++++++++++++++--
 1 file changed, 56 insertions(+), 3 deletions(-)

diff --git a/libudev/libudev-enumerate.c b/libudev/libudev-enumerate.c
index 96cf06090..986c1fc3d 100644
--- a/libudev/libudev-enumerate.c
+++ b/libudev/libudev-enumerate.c
@@ -190,7 +190,8 @@ static int syspath_cmp(const void *p1, const void *p2)
 	return ret;
 }
 
-static int devices_delay(struct udev *udev, const char *syspath)
+/* For devices that should be moved to the absolute end of the list */
+static int devices_delay_end(struct udev *udev, const char *syspath)
 {
 	static const char *delay_device_list[] = {
 		"/block/md",
@@ -210,6 +211,32 @@ static int devices_delay(struct udev *udev, const char *syspath)
 	return 0;
 }
 
+/* For devices that should just be moved a little bit later, just
+ * before the point where some common path prefix changes. Returns the
+ * number of characters that make up that common prefix */
+static size_t devices_delay_later(struct udev *udev, const char *syspath)
+{
+	const char *c;
+
+	/* For sound cards the control device must be enumerated last
+	 * to make sure it's the final device node that gets ACLs
+	 * applied. Applications rely on this fact and use ACL changes
+	 * on the control node as an indicator that the ACL change of
+	 * the entire sound card completed. The kernel makes this
+	 * guarantee when creating those devices, and hence we should
+	 * too when enumerating them. */
+
+	if ((c = strstr(syspath, "/sound/card"))) {
+		c += 11;
+		c += strcspn(c, "/");
+
+		if (strncmp(c, "/controlC", 9) == 0)
+			return c - syspath + 1;
+	}
+
+	return 0;
+}
+
 /**
  * udev_enumerate_get_list_entry:
  * @udev_enumerate: context
@@ -223,7 +250,8 @@ struct udev_list_entry *udev_enumerate_get_list_entry(struct udev_enumerate *ude
 	if (!udev_enumerate->devices_uptodate) {
 		unsigned int i;
 		unsigned int max;
-		struct syspath *prev = NULL;
+		struct syspath *prev = NULL, *move_later = NULL;
+		size_t move_later_prefix;
 
 		udev_list_cleanup_entries(udev_enumerate->udev, &udev_enumerate->devices_list);
 		qsort(udev_enumerate->devices, udev_enumerate->devices_cur, sizeof(struct syspath), syspath_cmp);
@@ -240,14 +268,39 @@ struct udev_list_entry *udev_enumerate_get_list_entry(struct udev_enumerate *ude
 			prev = entry;
 
 			/* skip to be delayed devices, and add them to the end of the list */
-			if (devices_delay(udev_enumerate->udev, entry->syspath)) {
+			if (devices_delay_end(udev_enumerate->udev, entry->syspath)) {
 				syspath_add(udev_enumerate, entry->syspath);
 				continue;
 			}
 
+			/* skip to be delayed devices, and move the to
+			 * the point where the prefix changes. We can
+			 * only move one item at a time. */
+			if (!move_later) {
+				move_later_prefix = devices_delay_later(udev_enumerate->udev, entry->syspath);
+
+				if (move_later_prefix > 0) {
+					move_later = entry;
+					continue;
+				}
+			}
+
+			if (move_later &&
+			    strncmp(entry->syspath, move_later->syspath, move_later_prefix) != 0) {
+
+				udev_list_entry_add(udev_enumerate->udev, &udev_enumerate->devices_list,
+					    move_later->syspath, NULL, 0, 0);
+				move_later = NULL;
+			}
+
 			udev_list_entry_add(udev_enumerate->udev, &udev_enumerate->devices_list,
 					    entry->syspath, NULL, 0, 0);
 		}
+
+		if (move_later)
+			udev_list_entry_add(udev_enumerate->udev, &udev_enumerate->devices_list,
+					    move_later->syspath, NULL, 0, 0);
+
 		/* add and cleanup delayed devices from end of list */
 		for (i = max; i < udev_enumerate->devices_cur; i++) {
 			struct syspath *entry = &udev_enumerate->devices[i];
-- 
2.30.2