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platform: resync route cache upon NLM_F_REPLACE flag

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There really is no way around this. As we don't cache all the routes
(e.g. ignored based on rtm_protocol or rtm_type), we cannot know which
route was replaced, when we get a NLM_F_REPLACE message.

We need to request a new dump in that case, which can be expensive, if
there are a lot of routes or if replace happens frequently.

The only possible solutions would be:

1) NetworkManager caches all routes, but it also needs to make sure to
  get *everything* right. In particular, to understand every relevant
  route attribute (including those added in the future, which is
  impossible).

2) kernel provides a reasonable API (rhbz#1337855, rhbz#1337860) that
  allows to sufficiently understand what is going on based on the
  netlink notifications.
This commit is contained in:
Thomas Haller 2022-10-28 20:17:57 +02:00
parent 4ec2123aa2
commit 6fc0dc3fcb
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GPG key ID: 29C2366E4DFC5728
1 changed files with 37 additions and 14 deletions
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51
src/libnm-platform/nmp-object.c
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@ -2978,14 +2978,45 @@ nmp_cache_update_netlink_route(NMPCache *cache,
nm_assert(cache);
nm_assert(NMP_OBJECT_IS_VALID(obj_hand_over));
nm_assert(!NMP_OBJECT_IS_STACKINIT(obj_hand_over));
/* A link object from netlink must have the udev related fields unset.
* We could implement to handle that, but there is no need to support such
* a use-case */
nm_assert(NM_IN_SET(NMP_OBJECT_GET_TYPE(obj_hand_over),
NMP_OBJECT_TYPE_IP4_ROUTE,
NMP_OBJECT_TYPE_IP6_ROUTE));
nm_assert(nm_dedup_multi_index_obj_find(cache->multi_idx, obj_hand_over) != obj_hand_over);
if (NM_FLAGS_HAS(nlmsgflags, NLM_F_REPLACE)) {
/* This means, that the message indicates that another route was replaced.
* Since we don't cache all routes (see "route_is_alive"), we cannot know
* with certainty which route was replaced.
*
* Even if we would cache *all* routes (which we cannot, if kernel adds new
* routing features that modify the known nmp_object_id_equal()), it would
* be hard to find the right route that was replaced. Well, probably we
* would have to keep NMP_CACHE_ID_TYPE_ROUTES_BY_WEAK_ID sorted by order
* of notifications, which is hard. The code below actually makes an effort
* to do that, but it's not actually used, because we just resync.
*
* The only proper solution for this would be to improve kernel with [1]
* and [2].
*
* [1] https://bugzilla.redhat.com/show_bug.cgi?id=1337855
* [2] https://bugzilla.redhat.com/show_bug.cgi?id=1337860
*
* We need to resync.
*/
if (NMP_OBJECT_GET_TYPE(obj_hand_over) == NMP_OBJECT_TYPE_IP4_ROUTE
&& !nmp_cache_lookup_all(cache, NMP_CACHE_ID_TYPE_ROUTES_BY_WEAK_ID, obj_hand_over)) {
/* For IPv4, we can do a small optimization. We skip the resync, if we have
* no conflicting routes (by weak-id).
*
* This optimization does not work for IPv6 (maybe should be fixed).
*/
} else {
entry_replace = NULL;
resync_required = TRUE;
goto out;
}
}
entry_old = _lookup_entry(cache, obj_hand_over);
entry_new = NULL;
@ -3033,19 +3064,11 @@ update_done:
if (is_dump)
goto out;
if (!entry_new) {
if (NM_FLAGS_HAS(nlmsgflags, NLM_F_REPLACE)
&& nmp_cache_lookup_all(cache, NMP_CACHE_ID_TYPE_ROUTES_BY_WEAK_ID, obj_hand_over)) {
/* hm. @obj_hand_over was not added, meaning it was not alive.
* However, we track some other objects with the same weak-id.
* It's unclear what that means. To be sure, resync. */
resync_required = TRUE;
}
if (!entry_new)
goto out;
}
/* FIXME: for routes, we only maintain the order correctly for the BY_WEAK_ID
* index. For all other indexes their order becomes messed up. */
/* For routes, we only maintain the order correctly for the BY_WEAK_ID
* index. For all other indexes, their order is not preserved. */
entry_cur =
_lookup_entry_with_idx_type(cache, NMP_CACHE_ID_TYPE_ROUTES_BY_WEAK_ID, entry_new->obj);
if (!entry_cur) {