archive, cio, cmd, linux: use buffer pools

To avoid buffer bloat in long running processes, we try to use buffer
pools where possible. This is meant to address shim memory usage issues,
but may not be the root cause.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

linux/bundle.go

@@ -3,9 +3,8 @@
 package linux
 
 import (
-	"bytes"
 	"context"
-	"io"
+	"io/ioutil"
 	"os"
 	"path/filepath"
 
@@ -52,12 +51,7 @@ func newBundle(id, path, workDir string, spec []byte) (b *bundle, err error) {
 	if err := os.Mkdir(filepath.Join(path, "rootfs"), 0711); err != nil {
 		return nil, err
 	}
-	f, err := os.Create(filepath.Join(path, configFilename))
-	if err != nil {
-		return nil, err
-	}
-	defer f.Close()
-	_, err = io.Copy(f, bytes.NewReader(spec))
+	err = ioutil.WriteFile(filepath.Join(path, configFilename), spec, 0666)
 	return &bundle{
 		id:      id,
 		path:    path,