Create server package for containerd daemon

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

server/config.go

@@ -0,0 +1,86 @@
+package server
+
+import (
+	"bytes"
+	"io"
+
+	"github.com/BurntSushi/toml"
+)
+
+// Config provides containerd configuration data for the server
+type Config struct {
+	// Root is the path to a directory where containerd will store persistent data
+	Root string `toml:"root"`
+	// GRPC configuration settings
+	GRPC GRPCConfig `toml:"grpc"`
+	// Debug and profiling settings
+	Debug Debug `toml:"debug"`
+	// Metrics and monitoring settings
+	Metrics MetricsConfig `toml:"metrics"`
+	// Snapshotter specifies which snapshot driver to use
+	Snapshotter string `toml:"snapshotter"`
+	// Differ specifies which differ to use. Differ is tightly coupled with the snapshotter
+	// so not all combinations may work.
+	Differ string `toml:"differ"`
+	// Plugins provides plugin specific configuration for the initialization of a plugin
+	Plugins map[string]toml.Primitive `toml:"plugins"`
+	// Enable containerd as a subreaper
+	Subreaper bool `toml:"subreaper"`
+	// OOMScore adjust the containerd's oom score
+	OOMScore int `toml:"oom_score"`
+
+	md toml.MetaData
+}
+
+type GRPCConfig struct {
+	Address string `toml:"address"`
+	Uid     int    `toml:"uid"`
+	Gid     int    `toml:"gid"`
+}
+
+type Debug struct {
+	Address string `toml:"address"`
+	Uid     int    `toml:"uid"`
+	Gid     int    `toml:"gid"`
+	Level   string `toml:"level"`
+}
+
+type MetricsConfig struct {
+	Address string `toml:"address"`
+}
+
+// Decode unmarshals a plugin specific configuration by plugin id
+func (c *Config) Decode(id string, v interface{}) (interface{}, error) {
+	data, ok := c.Plugins[id]
+	if !ok {
+		return v, nil
+	}
+	if err := c.md.PrimitiveDecode(data, v); err != nil {
+		return nil, err
+	}
+	return v, nil
+}
+
+// WriteTo marshals the config to the provided writer
+func (c *Config) WriteTo(w io.Writer) (int64, error) {
+	buf := bytes.NewBuffer(nil)
+	e := toml.NewEncoder(buf)
+	if err := e.Encode(c); err != nil {
+		return 0, err
+	}
+	return io.Copy(w, buf)
+}
+
+// LoadConfig loads the containerd server config from the provided path
+func LoadConfig(path string, v *Config) error {
+	if v == nil {
+		v = &Config{}
+	}
+	md, err := toml.DecodeFile(path, v)
+	if err != nil {
+		return err
+	}
+	v.md = md
+	return nil
+
+}