From f49145d5ff6b2c48fe243b74be240492ba75dec3 Mon Sep 17 00:00:00 2001
From: Alban Crequy <alban@kinvolk.io>
Date: Mon, 8 Feb 2016 23:28:15 +0100
Subject: [PATCH] new plugin: tuning

Allow users to tune net network parameters such as somaxconn.

With this patch, users can add a new network configuration:

> {
>   "name": "mytuning",
>   "type": "tuning",
>   "sysctl": {
>           "net.core.somaxconn": "500"
>   }
> }

The value /proc/sys/net/core/somaxconn will be set to 500 in the network
namespace but will remain unchanged on the host.

Only sysctl parameters that belong to the network subsystem can be
modified.

Related to: https://github.com/coreos/rkt/pull/2140
---
 Documentation/tuning.md       | 36 +++++++++++++++
 plugins/meta/tuning/tuning.go | 83 +++++++++++++++++++++++++++++++++++
 test                          |  2 +-
 3 files changed, 120 insertions(+), 1 deletion(-)
 create mode 100644 Documentation/tuning.md
 create mode 100644 plugins/meta/tuning/tuning.go

diff --git a/Documentation/tuning.md b/Documentation/tuning.md
new file mode 100644
index 00000000..bc786d88
--- /dev/null
+++ b/Documentation/tuning.md
@@ -0,0 +1,36 @@
+# tuning plugin
+
+## Overview
+
+This plugin can change some system controls (sysctls) in the network namespace.
+It does not create any network interfaces and therefore does not bring connectivity by itself.
+It is only useful when used in addition to other plugins.
+
+## Operation
+The following network configuration file
+```
+{
+  "name": "mytuning",
+  "type": "tuning",
+  "sysctl": {
+          "net.core.somaxconn": "500"
+  }
+}
+```
+will set /proc/sys/net/core/somaxconn to 500.
+Other sysctls can be modified as long as they belong to the network namespace (`/proc/sys/net/*`).
+
+A successful result would simply be:
+```
+{
+  "cniVersion": "0.1.0"
+}
+```
+
+## Network sysctls documentation
+
+Some network sysctls are documented in the Linux sources:
+
+- [Documentation/sysctl/net.txt](https://www.kernel.org/doc/Documentation/sysctl/net.txt)
+- [Documentation/networking/ip-sysctl.txt](https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt)
+- [Documentation/networking/](https://www.kernel.org/doc/Documentation/networking/)
diff --git a/plugins/meta/tuning/tuning.go b/plugins/meta/tuning/tuning.go
new file mode 100644
index 00000000..91118dfb
--- /dev/null
+++ b/plugins/meta/tuning/tuning.go
@@ -0,0 +1,83 @@
+// Copyright 2016 CNI 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.
+
+// This is a "meta-plugin". It reads in its own netconf, it does not create
+// any network interface but just changes the network sysctl.
+
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/appc/cni/pkg/ns"
+	"github.com/appc/cni/pkg/skel"
+	"github.com/appc/cni/pkg/types"
+)
+
+// TuningConf represents the network tuning configuration.
+type TuningConf struct {
+	types.NetConf
+	SysCtl map[string]string `json:"sysctl"`
+}
+
+func cmdAdd(args *skel.CmdArgs) error {
+	tuningConf := TuningConf{}
+	if err := json.Unmarshal(args.StdinData, &tuningConf); err != nil {
+		return fmt.Errorf("failed to load netconf: %v", err)
+	}
+
+	// The directory /proc/sys/net is per network namespace. Enter in the
+	// network namespace before writing on it.
+
+	err := ns.WithNetNSPath(args.Netns, false, func(hostNS *os.File) error {
+		for key, value := range tuningConf.SysCtl {
+			fileName := filepath.Join("/proc/sys", strings.Replace(key, ".", "/", -1))
+			fileName = filepath.Clean(fileName)
+
+			// Refuse to modify sysctl parameters that don't belong
+			// to the network subsystem.
+			if !strings.HasPrefix(fileName, "/proc/sys/net/") {
+				return fmt.Errorf("invalid net sysctl key: %q", key)
+			}
+			content := []byte(value)
+			err := ioutil.WriteFile(fileName, content, 0644)
+			if err != nil {
+				return err
+			}
+		}
+		return nil
+	})
+	if err != nil {
+		return err
+	}
+
+	result := types.Result{}
+	return result.Print()
+}
+
+func cmdDel(args *skel.CmdArgs) error {
+	// TODO: the settings are not reverted to the previous values. Reverting the
+	// settings is not useful when the whole container goes away but it could be
+	// useful in scenarios where plugins are added and removed at runtime.
+	return nil
+}
+
+func main() {
+	skel.PluginMain(cmdAdd, cmdDel)
+}
diff --git a/test b/test
index bd123ff6..6085cfe2 100755
--- a/test
+++ b/test
@@ -12,7 +12,7 @@ set -e
 source ./build
 
 TESTABLE="plugins/ipam/dhcp"
-FORMATTABLE="$TESTABLE libcni pkg/ip pkg/ns pkg/invoke pkg/types pkg/ipam pkg/skel plugins/ipam/host-local plugins/main/bridge plugins/meta/flannel"
+FORMATTABLE="$TESTABLE libcni pkg/ip pkg/ns pkg/invoke pkg/types pkg/ipam pkg/skel plugins/ipam/host-local plugins/main/bridge plugins/meta/flannel plugins/meta/tuning"
 
 # user has not provided PKG override
 if [ -z "$PKG" ]; then