platform: add index for links by ifname

Downsides:

  - Add some additional overhead to manage the index

  - The NMPCacheId struct grows to 16 bytes, affecting
    hashing performance for all object types.

Still do it, based on the assumption that it doesn't matter
for a low number of interfaces. But the O(1) access time matters
when having lots of interfaces.

src/platform/nmp-object.c

@@ -1072,6 +1072,24 @@ nmp_cache_id_init_routes_visible (NMPCacheId *id,
 	return id;
 }
 
+NMPCacheId *
+nmp_cache_id_init_link_by_ifname (NMPCacheId *id,
+                                  const char *ifname)
+{
+	gsize l;
+
+	_nmp_cache_id_init (id, NMP_CACHE_ID_TYPE_LINK_BY_IFNAME);
+
+	if (   !ifname
+	    || (l = strlen (ifname)) > sizeof (id->link_by_ifname.ifname_short))
+		g_return_val_if_reached (id);
+
+	/* the trailing NUL is dropped!! */
+	memcpy (id->link_by_ifname.ifname_short, ifname, l);
+
+	return id;
+}
+
 /******************************************************************/
 
 static gboolean
@@ -1095,6 +1113,23 @@ _nmp_object_init_cache_id (const NMPObject *obj, NMPCacheIdType id_type, NMPCach
 	}
 }
 
+static gboolean
+_vt_cmd_obj_init_cache_id_link (const NMPObject *obj, NMPCacheIdType id_type, NMPCacheId *id, const NMPCacheId **out_id)
+{
+	switch (id_type) {
+	case NMP_CACHE_ID_TYPE_LINK_BY_IFNAME:
+		if (obj->link.name[0]) {
+			*out_id = nmp_cache_id_init_link_by_ifname (id, obj->link.name);
+			return TRUE;
+		}
+		break;
+	default:
+		return FALSE;
+	}
+	*out_id = NULL;
+	return TRUE;
+}
+
 static gboolean
 _vt_cmd_obj_init_cache_id_ipx_address (const NMPObject *obj, NMPCacheIdType id_type, NMPCacheId *id, const NMPCacheId **out_id)
 {
@@ -1356,7 +1391,7 @@ nmp_cache_lookup_link_full (const NMPCache *cache,
 	const NMPObject *obj;
 	const NMPlatformObject *const *list;
 	guint i, len;
-	NMPCacheId cache_id;
+	NMPCacheId cache_id, *p_cache_id;
 
 	if (ifindex > 0) {
 		obj = nmp_cache_lookup_obj (cache, nmp_object_stackinit_id_link (&obj_needle, ifindex));
@@ -1371,7 +1406,14 @@ nmp_cache_lookup_link_full (const NMPCache *cache,
 	} else if (!ifname && !match_fn)
 		return NULL;
 	else {
-		list = nmp_cache_lookup_multi (cache, nmp_cache_id_init_object_type (&cache_id, NMP_OBJECT_TYPE_LINK, visible_only), &len);
+		if (   ifname
+		    && strlen (ifname) <= sizeof (cache_id.link_by_ifname.ifname_short)) {
+			p_cache_id = nmp_cache_id_init_link_by_ifname (&cache_id, ifname);
+			ifname = NULL;
+		} else
+			p_cache_id = nmp_cache_id_init_object_type (&cache_id, NMP_OBJECT_TYPE_LINK, visible_only);
+
+		list = nmp_cache_lookup_multi (cache, p_cache_id, &len);
 		for (i = 0; i < len; i++) {
 			obj = NMP_OBJECT_UP_CAST (list[i]);
 
@@ -1933,6 +1975,7 @@ const NMPClass _nmp_classes[NMP_OBJECT_TYPE_MAX] = {
 		.rtm_gettype                        = RTM_GETLINK,
 		.signal_type_id                     = NM_PLATFORM_SIGNAL_ID_LINK,
 		.signal_type                        = NM_PLATFORM_SIGNAL_LINK_CHANGED,
+		.cmd_obj_init_cache_id              = _vt_cmd_obj_init_cache_id_link,
 		.cmd_obj_cmp                        = _vt_cmd_obj_cmp_link,
 		.cmd_obj_copy                       = _vt_cmd_obj_copy_link,
 		.cmd_obj_stackinit_id               = _vt_cmd_obj_stackinit_id_link,

src/platform/nmp-object.h

@@ -64,6 +64,9 @@ typedef enum { /*< skip >*/
 	/* all the objects of a certain type */
 	NMP_CACHE_ID_TYPE_OBJECT_TYPE,
 
+	/* index for the link objects by ifname. */
+	NMP_CACHE_ID_TYPE_LINK_BY_IFNAME,
+
 	/* all the visible objects of a certain type */
 	NMP_CACHE_ID_TYPE_OBJECT_TYPE_VISIBLE_ONLY,
 
@@ -104,6 +107,11 @@ typedef struct {
 			guint8 obj_type; /* NMPObjectType as guint8 */
 			int ifindex;
 		} object_type_by_ifindex;
+		struct {
+			/* NMP_CACHE_ID_TYPE_LINK_BY_IFNAME */
+			guint8 _id_type;
+			char ifname_short[IFNAMSIZ - 1]; /* don't include the trailing NUL so the struct fits in 4 bytes. */
+		} link_by_ifname;
 	};
 } NMPCacheId;
 
@@ -374,6 +382,7 @@ void nmp_cache_id_destroy (NMPCacheId *id);
 NMPCacheId *nmp_cache_id_init_object_type (NMPCacheId *id, NMPObjectType obj_type, gboolean visible_only);
 NMPCacheId *nmp_cache_id_init_addrroute_visible_by_ifindex (NMPCacheId *id, NMPObjectType obj_type, int ifindex);
 NMPCacheId *nmp_cache_id_init_routes_visible (NMPCacheId *id, NMPObjectType obj_type, gboolean with_default, gboolean with_non_default, int ifindex);
+NMPCacheId *nmp_cache_id_init_link_by_ifname (NMPCacheId *id, const char *ifname);
 
 const NMPlatformObject *const *nmp_cache_lookup_multi (const NMPCache *cache, const NMPCacheId *cache_id, guint *out_len);
 GArray *nmp_cache_lookup_multi_to_array (const NMPCache *cache, NMPObjectType obj_type, const NMPCacheId *cache_id);