[libvirt PATCH] virnetdevbridge: Ignore EEXIST when adding an entry to fdb

[Jiri Denemark]

When updating entries in a bridge forwarding database (i.e., when
macTableManager='libvirt' is configured for the bridge), we may end up
in a situation when the entry we want to add is already present. Let's
just ignore the error in such a case.

This fixes an error to resume a domain when fdb entries were not
properly removed when the domain was paused:

    virsh # resume test
    error: Failed to resume domain test
    error: error adding fdb entry for vnet2: File exists

For some reason, fdb entries are only removed when libvirt explicitly
stops CPUs, but nothing happens when we just get STOP event from QEMU.
An alternative approach would be to make sure we always remove the
entries regardless on why a domain was paused (e.g., during migration),
but that would be a significantly more disruptive change with possible
side effects.

Signed-off-by: Jiri Denemark <jdenemar at redhat.com>
---
 src/util/virnetdevbridge.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/src/util/virnetdevbridge.c b/src/util/virnetdevbridge.c
index 7b5ea4fe1d..4fe84cc162 100644
--- a/src/util/virnetdevbridge.c
+++ b/src/util/virnetdevbridge.c
@@ -1063,9 +1063,13 @@ virNetDevBridgeFDBAddDel(const virMacAddr *mac, const char *ifname,
         if (resp->nlmsg_len < NLMSG_LENGTH(sizeof(*err)))
             goto malformed_resp;
         if (err->error) {
-            virReportSystemError(-err->error,
-                                 _("error adding fdb entry for %s"), ifname);
-            return -1;
+            if (isAdd && -err->error == EEXIST) {
+                VIR_DEBUG("fdb entry for %s already exists", ifname);
+            } else {
+                virReportSystemError(-err->error,
+                                     _("error adding fdb entry for %s"), ifname);
+                return -1;
+            }
         }
         break;
     case NLMSG_DONE:
-- 
2.31.1