Add ENOBUFS handling for unsolicited messages

src/framed.rs

@@ -5,6 +5,7 @@ use std::{
     fmt::Debug,
     io,
     marker::PhantomData,
+    mem::size_of,
     pin::Pin,
     task::{Context, Poll},
 };
@@ -17,9 +18,13 @@ use crate::{
     sys::{AsyncSocket, SocketAddr},
 };
 use netlink_packet_core::{
-    NetlinkDeserializable, NetlinkMessage, NetlinkSerializable,
+    NetlinkDeserializable, NetlinkHeader, NetlinkMessage, NetlinkPayload,
+    NetlinkSerializable, NLMSG_OVERRUN,
 };
 
+/// Buffer overrun condition
+const ENOBUFS: i32 = 105;
+
 pub struct NetlinkFramed<T, S, C> {
     socket: S,
     // see https://doc.rust-lang.org/nomicon/phantom-data.html
@@ -68,6 +73,30 @@ where
 
             *in_addr = match ready!(socket.poll_recv_from(cx, reader)) {
                 Ok(addr) => addr,
+                // When receiving messages in multicast mode (i.e. we subscribed
+                // to notifications), the kernel will not wait
+                // for us to read datagrams before sending more.
+                // The receive buffer has a finite size, so once it is full (no
+                // more message can fit in), new messages will be dropped and
+                // recv calls will return `ENOBUFS`.
+                // This needs to be handled for applications to resynchronize
+                // with the contents of the kernel if necessary.
+                // We don't need to do anything special:
+                // - contents of the reader is still valid because we won't have
+                //   partial messages in there anyways (large enough buffer)
+                // - contents of the socket's internal buffer is still valid
+                //   because the kernel won't put partial data in it
+                Err(e) if e.raw_os_error() == Some(ENOBUFS) => {
+                    warn!("netlink socket buffer full");
+                    let mut hdr = NetlinkHeader::default();
+                    hdr.length = size_of::<NetlinkHeader>() as u32;
+                    hdr.message_type = NLMSG_OVERRUN;
+                    let msg = NetlinkMessage::new(
+                        hdr,
+                        NetlinkPayload::Overrun(Vec::new()),
+                    );
+                    return Poll::Ready(Some((msg, SocketAddr::new(0, 0))));
+                }
                 Err(e) => {
                     error!("failed to read from netlink socket: {:?}", e);
                     return Poll::Ready(None);