[ovs-dev] [PATCH] netdev-linux: Do not log a warning if the device is down.

[Ben Pfaff]

On Fri, Jun 10, 2016 at 03:52:16PM -0700, Daniele Di Proietto wrote:
> In the userspace datapath we use tap devices as internal netdev.  The
> datapath doesn't consider whether a device is up or down before sending
> to it, and so far this hasn't been a problem.
> 
> Since Linux upstream commit 1bd4978a88ac("tun: honor IFF_UP in
> tun_get_user()"), included in 4.4, writing to a tap device that is not
> up sets errno to EIO.  This commit avoids printing a warning in this
> case.
> 
> This fixes a failures in the system-userspace-testsuites.
> 
> Reported-by: Joe Stringer <joe at ovn.org>
> Signed-off-by: Daniele Di Proietto <diproiettod at vmware.com>

Acked-by: Ben Pfaff <blp at ovn.org>

However, the logic is getting a little nonobvious here in my opinion.
Here's a version that I think is equivalent (I have not tested it) and
seems to me easier to understand:

diff --git a/lib/netdev-linux.c b/lib/netdev-linux.c
index ef11d12..1cc0a5f 100644
--- a/lib/netdev-linux.c
+++ b/lib/netdev-linux.c
@@ -1223,15 +1223,20 @@ netdev_linux_send(struct netdev *netdev_, int qid OVS_UNUSED,
         }
 
         if (retval < 0) {
-            /* The Linux AF_PACKET implementation never blocks waiting for room
-             * for packets, instead returning ENOBUFS.  Translate this into
-             * EAGAIN for the caller. */
-            error = errno == ENOBUFS ? EAGAIN : errno;
-            if (error == EINTR) {
-                /* continue without incrementing 'i', i.e. retry this packet */
+            if (errno == EINTR) {
+                /* The send was interrupted by a signal.  Retry the packet by
+                 * continuing without incrementing 'i'. */
                 continue;
+            } else if (errno == EIO && is_tap_netdev(netdev_)) {
+                /* The Linux tap driver returns EIO if the device is not up.
+                 * From the OVS side this is not an error, so ignore it. */
+            } else {
+                /* The Linux AF_PACKET implementation never blocks waiting for
+                 * room for packets, instead returning ENOBUFS.  Translate this
+                 * into EAGAIN for the caller. */
+                error = errno == ENOBUFS ? EAGAIN : errno;
+                break;
             }
-            break;
         } else if (retval != size) {
             VLOG_WARN_RL(&rl, "sent partial Ethernet packet (%"PRIuSIZE" bytes"
                               " of %"PRIuSIZE") on %s", retval, size,