error: Kill @error_warn

We added @error_warn some two years ago in commit 3ffef1a55ca (error:
add global &error_warn destination).  It has multiple issues:

* error.h's big comment was not updated for it.

* Function contracts were not updated for it.

* ERRP_GUARD() is unaware of @error_warn, and fails to mask it from
  error_prepend() and such.  These crash on @error_warn, as pointed
  out by Akihiko Odaki.

All fixable.  However, after more than two years, we had just of 15
uses, of which the last few patches removed seven as unclean or
otherwise undesirable, adding back five elsewhere.  I didn't look
closely enough at the remaining seven to decide whether they are
desirable or not.

I don't think this feature earns its keep.  Drop it.

Thanks-to: Akihiko  Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Message-ID: <20250923091000.3180122-14-armbru@redhat.com>
Reviewed-by: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>

1 files changed, 7 insertions, 1 deletions

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 6b5b5dace3..7848e26278 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -1289,6 +1289,8 @@ exit:
 
 static bool virtio_net_load_ebpf(VirtIONet *n, Error **errp)
 {
+    Error *err = NULL;
+
     if (!virtio_net_attach_ebpf_to_backend(n->nic, -1)) {
         return true;
     }
@@ -1306,7 +1308,11 @@ static bool virtio_net_load_ebpf(VirtIONet *n, Error **errp)
         return virtio_net_load_ebpf_fds(n, errp);
     }
 
-    ebpf_rss_load(&n->ebpf_rss, &error_warn);
+    ebpf_rss_load(&n->ebpf_rss, &err);
+    /* Beware, ebpf_rss_load() can return false with @err unset */
+    if (err) {
+        warn_report_err(err);
+    }
     return true;
 }