Skip loading openvswitch Kernel module if built-in

If a module is built-in, trying to load the module with modprobe inside
a container may fail (insted of just being a no-op). This will cause
Antrea initialization to fail unless agent.dontLoadKernelModules is
explicitly set to true.

Now that the Docker Desktop LinuxKit VM comes with openvswitch built-in
(starting with 4.27.0), trying to install "default" Antrea (i.e.,
without setting agent.dontLoadKernelModules) in a Kind cluster running
with Docker Desktop on macOS will fail. To make sure that users will not
run into this issue, we add logic to the install_cni script to skip the
modprobe call if the module is built-in.

After this agent, there should be very limited use cases for the
agent.dontLoadKernelModules parameter, but there is no harm in keeping
in case it is needed in the future or for some corner cases.

I also realized that the "--skip-kmod" flag for the start_ovs script did
not provide any value. Either the openvswitch module needs to be
explicitly loaded, in which case the install_cni script will take care
of it anyway, or it should not be loaded at all (e.g., because it is
built-in). Additionally, because we do not mount the host's /lib/modules
to the antrea-ovs container, it is not possible to load any kernel
module from the container.

Fixes antrea-io#5939

Signed-off-by: Antonin Bas <antonin.bas@broadcom.com>

build/charts/antrea/README.md

@@ -39,7 +39,7 @@ Kubernetes: `>= 1.16.0-0`
 | agent.antreaOVS.securityContext.privileged | bool | `false` | Run the antrea-ovs container as privileged. |
 | agent.apiPort | int | `10350` | Port for the antrea-agent APIServer to serve on. |
 | agent.dnsPolicy | string | `""` | DNS Policy for the antrea-agent Pods. If empty, the Kubernetes default will be used. |
-| agent.dontLoadKernelModules | bool | `false` | Do not try to load any of the required Kernel modules (e.g., openvswitch) during initialization of the antrea-agent. Most users should never need to set this to true, but it may be required with some specific distributions. |
+| agent.dontLoadKernelModules | bool | `false` | Do not try to load any of the required Kernel modules (e.g., openvswitch) during initialization of the antrea-agent. Most users should never need to set this to true, but it may be required with some specific distributions. Note that we will never try to load a module if we can detect that it is "built-in", regardless of this value. |
 | agent.enablePrometheusMetrics | bool | `true` | Enable metrics exposure via Prometheus. |
 | agent.extraVolumes | list | `[]` | Additional volumes for antrea-agent Pods. |
 | agent.installCNI.extraEnv | object | `{}` | Extra environment variables to be injected into install-cni. |

build/charts/antrea/templates/agent/daemonset.yaml

@@ -267,9 +267,6 @@ spec:
             {{- if .Values.ovs.hwOffload }}
             - "--hw-offload"
             {{- end }}
-            {{- if .Values.agent.dontLoadKernelModules }}
-            - "--skip-kmod"
-            {{- end }}
             {{- with .Values.agent.antreaOVS.extraArgs }}
             {{- toYaml . | trim | nindent 12 }}
             {{- end }}

build/charts/antrea/values.yaml

@@ -245,6 +245,8 @@ agent:
   # -- Do not try to load any of the required Kernel modules (e.g., openvswitch)
   # during initialization of the antrea-agent. Most users should never need to
   # set this to true, but it may be required with some specific distributions.
+  # Note that we will never try to load a module if we can detect that it is
+  # "built-in", regardless of this value.
   dontLoadKernelModules: false
   installCNI:
     # -- Extra environment variables to be injected into install-cni.

build/images/scripts/install_cni

@@ -16,6 +16,8 @@
 
 set -euo pipefail
 
+source module_utils
+
 # Fetching the list of the binaries that user wants to skip installing.
 IFS=',' read -r -a binaries <<< "${SKIP_CNI_BINARIES:-}"
 # Todo: check version and continue installation only for a newer version
@@ -55,12 +57,21 @@ install -m 644 /etc/antrea/antrea-cni.conflist /host/etc/cni/net.d/10-antrea.con
 rm -f /host/etc/cni/net.d/10-antrea.conf
 
 if [[ -z "${SKIP_LOADING_KERNEL_MODULES:-}" ]]; then
-    # Load the OVS kernel module
-    modprobe openvswitch || (echo "Failed to load the OVS kernel module from the container, try running 'modprobe openvswitch' on your Nodes"; exit 1)
+    # Load the OVS kernel module if not built-in
+    if ! is_module_builtin "openvswitch"; then
+        modprobe openvswitch || (echo "Failed to load the OVS kernel module from the container, try running 'modprobe openvswitch' on your Nodes"; exit 1)
+    else
+        echo "Module openvswitch is built-in"
+    fi
 
-    # Load the WireGuard kernel module. This is only required when WireGuard encryption is enabled.
-    # We could parse the antrea config file in the init-container to dynamically load this kernel module in the future.
-    modprobe wireguard || (echo "Failed to load the WireGuard kernel module, WireGuard encryption will not be available")
+    # Load the WireGuard kernel module if not built-in. This is only required when WireGuard
+    # encryption is enabled. We could parse the antrea config file in the init-container to
+    # dynamically load this kernel module in the future.
+    if ! is_module_builtin "wireguard"; then
+        modprobe wireguard || (echo "Failed to load the WireGuard kernel module, WireGuard encryption will not be available")
+    else
+        echo "Module wireguard is built-in"
+    fi
 fi
 
 # Change the default permissions of the run directory.

build/images/scripts/install_cni_chaining

@@ -15,6 +15,7 @@
 # limitations under the License.
 
 source logging
+source module_utils
 
 HOST_CNI_NET_DIR="/host/etc/cni/net.d"
 
@@ -124,8 +125,15 @@ update_cni_conf
 install -m 755 /usr/local/bin/antrea-cni /host/opt/cni/bin/antrea
 
 id
-# Load the OVS kernel module
-modprobe openvswitch || { echo "Failed to load the OVS kernel module from the container, try running 'modprobe openvswitch' on your Nodes"; exit 1;}
+
+if [[ -z "${SKIP_LOADING_KERNEL_MODULES:-}" ]]; then
+    # Load the OVS kernel module if not built-in
+    if ! is_module_builtin "openvswitch"; then
+        modprobe openvswitch || { echo "Failed to load the OVS kernel module from the container, try running 'modprobe openvswitch' on your Nodes"; exit 1;}
+    else
+        log_info "install_cni_chaining" "Module openvswitch is built-in"
+    fi
+fi
 
 if [[ "$run_monitor" == "false" ]]; then
     exit 0

build/images/scripts/module_utils

@@ -0,0 +1,19 @@
+# Copyright 2024 Antrea Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+function is_module_builtin {
+    local module="$1"
+    local path="/lib/modules/$(uname -r)/modules.builtin"
+    grep -q "$module\.ko" "$path"
+}

build/images/scripts/start_ovs

@@ -24,15 +24,13 @@ OVS_DB_FILE="${OVS_RUN_DIR}/conf.db"
 OVS_LOGROTATE_CONF="/etc/logrotate.d/openvswitch-switch"
 
 hw_offload="false"
-skip_kmod="false"
 log_file_max_num=0
 log_file_max_size=0
 
 function usage {
     echo "start_ovs"
     echo -e "  -h|--help\t\t \tPrint help message"
     echo -e "  --hw-offload\t\t \tEnable OVS hardware offload"
-    echo -e "  --skip-kmod\t\t \tForce skip Kernel module loading in OVS start script"
     echo -e "  --log_file_max_num=<uint> \tMaximum number of log files to be kept for an OVS daemon. Value 0 means keeping the current value"
     echo -e "  --log_file_max_size=<uint> \tMaximum size (in megabytes) of an OVS log file. Value 0 means keeping the current value"
 }
@@ -47,7 +45,7 @@ while (( "$#" )); do
       hw_offload="true"
       ;;
     --skip-kmod)
-      skip_kmod="true"
+      echo "--skip-kmod is deprecated and will be removed in the future; it is now the default behavior" >&2
       ;;
     --log_file_max_num=*)
       log_file_max_num=$1
@@ -149,15 +147,15 @@ set -euo pipefail
 # exit with code 128 + SIGNAL
 trap "quit" INT TERM
 
-if [ "$skip_kmod" == "true" ]; then
-    # ovs-ctl start will invoke ovs-kmod-ctl to load the openvswitch Kernel module if necessary
-    # (using modprobe). In some cases, this can fail unexpectedly, for example, with Talos Linux
-    # (see https://github.com/antrea-io/antrea/issues/5707). This is why this script offers the
-    # skip-kmod flag, which prevents the ovs-ctl script from trying to load any Kernel module. In
-    # order for this to work, we need to turn ovs-kmod-ctl into a "no-op".
-    cp /usr/share/openvswitch/scripts/ovs-kmod-ctl /usr/share/openvswitch/scripts/ovs-kmod-ctl.bak
-    echo ":" > /usr/share/openvswitch/scripts/ovs-kmod-ctl
-fi
+# ovs-ctl start will invoke ovs-kmod-ctl to load the openvswitch Kernel module
+# if necessary (using modprobe).
+# We want to avoid this behavior for the following reasons:
+#  * the initContainer is already in charge of loading the module if necessary
+#  * we do not mount the host's /lib/module directory into the antrea-ovs container
+#  * in some cases, modprobe will fail if the module is built-in
+# Therefore, we turn ovs-kmod-ctl into a "no-op".
+cp /usr/share/openvswitch/scripts/ovs-kmod-ctl /usr/share/openvswitch/scripts/ovs-kmod-ctl.bak
+echo ":" > /usr/share/openvswitch/scripts/ovs-kmod-ctl
 
 update_logrotate_config_file