platform: sort slaves after their master devices

Slaves should get sorted after their masters so that when generating
connections, the NMManager knows about the masters already.

The convoluted logic here is to ensure that:

1) the kernel doesn't pass bad information that causes NM to crash
or infinite loop

2) that with complicated parent/child relationships (like a VLAN interface
with a parent that is also a slave), children always get sorted after
*all* of their ancestors.  The previous code was only sorting children
after their immediate parent/master's ifindex, but not actually after
the parent in the returned list.

src/platform/nm-platform.c

@@ -267,37 +267,6 @@ nm_platform_query_devices (void)
 	g_array_unref (links_array);
 }
 
-static int
-compare_links (gconstpointer a, gconstpointer b)
-{
-	NMPlatformLink *link_a = (NMPlatformLink *) a;
-	NMPlatformLink *link_b = (NMPlatformLink *) b;
-	int sortindex_a, sortindex_b;
-
-	/* We mostly want to sort by ifindex. However, slaves should sort
-	 * before their masters, and children (eg, VLANs) should sort after
-	 * their parents.
-	 */
-	if (link_a->master)
-		sortindex_a = link_a->master * 3 - 1;
-	else if (link_a->parent)
-		sortindex_a = link_a->parent * 3 + 1;
-	else
-		sortindex_a = link_a->ifindex * 3;
-
-	if (link_b->master)
-		sortindex_b = link_b->master * 3 - 1;
-	else if (link_b->parent)
-		sortindex_b = link_b->parent * 3 + 1;
-	else
-		sortindex_b = link_b->ifindex * 3;
-
-	if (sortindex_a == sortindex_b)
-		return link_a->ifindex - link_b->ifindex;
-	else
-		return sortindex_a - sortindex_b;
-}
-
 /**
  * nm_platform_link_get_all:
  *
@@ -307,15 +276,100 @@ compare_links (gconstpointer a, gconstpointer b)
 GArray *
 nm_platform_link_get_all (void)
 {
-	GArray *links;
+	GArray *links, *result;
+	guint i, j, nresult;
+	GHashTable *unseen;
+	NMPlatformLink *item;
 
 	reset_error ();
 
 	g_return_val_if_fail (klass->link_get_all, NULL);
 
 	links = klass->link_get_all (platform);
-	g_array_sort (links, compare_links);
-	return links;
+
+	if (!links || links->len == 0)
+		return links;
+
+	unseen = g_hash_table_new (g_direct_hash, g_direct_equal);
+	for (i = 0; i < links->len; i++) {
+		item = &g_array_index (links, NMPlatformLink, i);
+
+		if (item->ifindex <= 0 || g_hash_table_contains (unseen, GINT_TO_POINTER (item->ifindex))) {
+			g_warn_if_reached ();
+			item->ifindex = 0;
+			continue;
+		}
+
+		g_hash_table_insert (unseen, GINT_TO_POINTER (item->ifindex), NULL);
+	}
+
+#ifndef G_DISABLE_ASSERT
+	/* Ensure that link_get_all returns a consistent and valid result. */
+	for (i = 0; i < links->len; i++) {
+		item = &g_array_index (links, NMPlatformLink, i);
+
+		if (!item->ifindex)
+			continue;
+		if (item->master != 0) {
+			g_warn_if_fail (item->master > 0);
+			g_warn_if_fail (item->master != item->ifindex);
+			g_warn_if_fail (g_hash_table_contains (unseen, GINT_TO_POINTER (item->master)));
+		}
+		if (item->parent != 0) {
+			g_warn_if_fail (item->parent > 0);
+			g_warn_if_fail (item->parent != item->ifindex);
+			g_warn_if_fail (g_hash_table_contains (unseen, GINT_TO_POINTER (item->parent)));
+		}
+	}
+#endif
+
+	/* Re-order the links list such that children/slaves come after all ancestors */
+	nresult = g_hash_table_size (unseen);
+	result = g_array_sized_new (TRUE, TRUE, sizeof (NMPlatformLink), nresult);
+	g_array_set_size (result, nresult);
+
+	j = 0;
+	do {
+		gboolean found_something = FALSE;
+		guint first_idx = G_MAXUINT;
+
+		for (i = 0; i < links->len; i++) {
+			item = &g_array_index (links, NMPlatformLink, i);
+
+			if (!item->ifindex)
+				continue;
+
+			if (first_idx == G_MAXUINT)
+				first_idx = i;
+
+			g_assert (g_hash_table_contains (unseen, GINT_TO_POINTER (item->ifindex)));
+
+			if (item->master > 0 && g_hash_table_contains (unseen, GINT_TO_POINTER (item->master)))
+				continue;
+			if (item->parent > 0 && g_hash_table_contains (unseen, GINT_TO_POINTER (item->parent)))
+				continue;
+
+			g_hash_table_remove (unseen, GINT_TO_POINTER (item->ifindex));
+			g_array_index (result, NMPlatformLink, j++) = *item;
+			item->ifindex = 0;
+			found_something = TRUE;
+		}
+
+		if (!found_something) {
+			/* there is a circle, pop the first (remaining) element from the list */
+			g_warn_if_reached ();
+			item = &g_array_index (links, NMPlatformLink, first_idx);
+
+			g_hash_table_remove (unseen, GINT_TO_POINTER (item->ifindex));
+			g_array_index (result, NMPlatformLink, j++) = *item;
+			item->ifindex = 0;
+		}
+	} while (j < nresult);
+
+	g_hash_table_destroy (unseen);
+	g_array_free (links, TRUE);
+
+	return result;
 }
 
 /**