From: Yohei Kojima This patch fixes the edge case behavior on ifup/ifdown and linking/unlinking two netdevsim interfaces: 1. unlink two interfaces netdevsim1 and netdevsim2 2. ifdown netdevsim1 3. ifup netdevsim1 4. link two interfaces netdevsim1 and netdevsim2 5. (Now two interfaces are linked in terms of netdevsim peer, but carrier state of the two interfaces remains DOWN.) This inconsistent behavior is caused by the current implementation, which only cares about the "link, then ifup" order, not "ifup, then link" order. This patch fixes the inconsistency by calling netif_carrier_on() when two netdevsim interfaces are linked. This patch fixes buggy behavior on NetworkManager-based systems which causes the netdevsim test to fail with the following error: # timeout set to 600 # selftests: drivers/net/netdevsim: peer.sh # 2025/12/25 00:54:03 socat[9115] W address is opened in read-write mode but only supports read-only # 2025/12/25 00:56:17 socat[9115] W connect(7, AF=2 192.168.1.1:1234, 16): Connection timed out # 2025/12/25 00:56:17 socat[9115] E TCP:192.168.1.1:1234: Connection timed out # expected 3 bytes, got 0 # 2025/12/25 00:56:17 socat[9109] W exiting on signal 15 not ok 13 selftests: drivers/net/netdevsim: peer.sh # exit=1 This patch also solves timeout on TCP Fast Open (TFO) test in NetworkManager-based systems because it also depends on netdevsim's carrier consistency. Fixes: 1a8fed52f7be ("netdevsim: set the carrier when the device goes up") Signed-off-by: Yohei Kojima --- drivers/net/netdevsim/bus.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/net/netdevsim/bus.c b/drivers/net/netdevsim/bus.c index 70e8c38ddad6..fa94c680c92a 100644 --- a/drivers/net/netdevsim/bus.c +++ b/drivers/net/netdevsim/bus.c @@ -332,6 +332,9 @@ static ssize_t link_device_store(const struct bus_type *bus, const char *buf, si rcu_assign_pointer(nsim_a->peer, nsim_b); rcu_assign_pointer(nsim_b->peer, nsim_a); + netif_carrier_on(dev_a); + netif_carrier_on(dev_b); + out_err: put_net(ns_b); put_net(ns_a); @@ -381,6 +384,9 @@ static ssize_t unlink_device_store(const struct bus_type *bus, const char *buf, if (!peer) goto out_put_netns; + netif_carrier_off(dev); + netif_carrier_off(peer->netdev); + err = 0; RCU_INIT_POINTER(nsim->peer, NULL); RCU_INIT_POINTER(peer->peer, NULL); -- 2.51.2 From: Yohei Kojima This commit adds a test case for netdevsim carrier state consistency. Specifically, the added test verifies the carrier state during the following operations: 1. Unlink two netdevsims 2. ifdown one netdevsim, then ifup again 3. Link the netdevsims again 4. ifdown one netdevsim, then ifup again These steps verifies that the carrier is UP iff two netdevsims are linked and ifuped. Signed-off-by: Yohei Kojima --- .../selftests/drivers/net/netdevsim/peer.sh | 63 +++++++++++++++++++ 1 file changed, 63 insertions(+) diff --git a/tools/testing/selftests/drivers/net/netdevsim/peer.sh b/tools/testing/selftests/drivers/net/netdevsim/peer.sh index 7f32b5600925..4ca994d2aa31 100755 --- a/tools/testing/selftests/drivers/net/netdevsim/peer.sh +++ b/tools/testing/selftests/drivers/net/netdevsim/peer.sh @@ -52,6 +52,43 @@ cleanup_ns() ip netns del nssv } +is_carrier_up() +{ + local netns="$1" + local nsim_dev="$2" + + # 0: DOWN + # 1: UP + local is_up=$(ip netns exec "$netns" \ + cat /sys/class/net/"$nsim_dev"/carrier 2>/dev/null) + + test "$is_up" -eq 1 +} + +assert_carrier_up() +{ + local netns="$1" + local nsim_dev="$2" + + if ! is_carrier_up "$netns" "$nsim_dev"; then + echo "$nsim_dev's carrier should be UP, but it isn't" + cleanup_ns + exit 1 + fi +} + +assert_carrier_down() +{ + local netns="$1" + local nsim_dev="$2" + + if is_carrier_up "$netns" "$nsim_dev"; then + echo "$nsim_dev's carrier should be DOWN, but it isn't" + cleanup_ns + exit 1 + fi +} + ### ### Code start ### @@ -113,6 +150,32 @@ if [ $? -eq 0 ]; then exit 1 fi +# netdevsim carrier state consistency checking +assert_carrier_up nssv "$NSIM_DEV_1_NAME" +assert_carrier_up nscl "$NSIM_DEV_2_NAME" + +echo "$NSIM_DEV_1_FD:$NSIM_DEV_1_IFIDX" > $NSIM_DEV_SYS_UNLINK + +assert_carrier_down nssv "$NSIM_DEV_1_NAME" +assert_carrier_down nscl "$NSIM_DEV_2_NAME" + +ip netns exec nssv ip link set dev "$NSIM_DEV_1_NAME" down +ip netns exec nssv ip link set dev "$NSIM_DEV_1_NAME" up + +assert_carrier_down nssv "$NSIM_DEV_1_NAME" +assert_carrier_down nscl "$NSIM_DEV_2_NAME" + +echo "$NSIM_DEV_1_FD:$NSIM_DEV_1_IFIDX $NSIM_DEV_2_FD:$NSIM_DEV_2_IFIDX" > $NSIM_DEV_SYS_LINK + +assert_carrier_up nssv "$NSIM_DEV_1_NAME" +assert_carrier_up nscl "$NSIM_DEV_2_NAME" + +ip netns exec nssv ip link set dev "$NSIM_DEV_1_NAME" down +ip netns exec nssv ip link set dev "$NSIM_DEV_1_NAME" up + +assert_carrier_up nssv "$NSIM_DEV_1_NAME" +assert_carrier_up nscl "$NSIM_DEV_2_NAME" + # send/recv packets tmp_file=$(mktemp) -- 2.51.2