Abstract to SocketAddress

This updates some methods for cross platform use as well as unifying
_unix files.

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

runtime/v2/shim/util_unix.go

@@ -1,4 +1,4 @@
-// +build !linux,!windows
+// +build !windows
 
 /*
    Copyright The containerd Authors.
@@ -19,7 +19,16 @@
 package shim
 
 import (
+	"context"
+	"net"
+	"path/filepath"
+	"strings"
 	"syscall"
+	"time"
+
+	"github.com/containerd/containerd/namespaces"
+	"github.com/containerd/containerd/sys"
+	"github.com/pkg/errors"
 )
 
 func getSysProcAttr() *syscall.SysProcAttr {
@@ -30,5 +39,32 @@ func getSysProcAttr() *syscall.SysProcAttr {
 
 // SetScore sets the oom score for a process
 func SetScore(pid int) error {
-	return nil
+	return sys.SetOOMScore(pid, sys.OOMScoreMaxKillable)
+}
+
+// SocketAddress returns an abstract socket address
+func SocketAddress(ctx context.Context, id string) (string, error) {
+	ns, err := namespaces.NamespaceRequired(ctx)
+	if err != nil {
+		return "", err
+	}
+	return filepath.Join(string(filepath.Separator), "containerd-shim", ns, id, "shim.sock"), nil
+}
+
+// AnonDialer returns a dialer for an abstract socket
+func AnonDialer(address string, timeout time.Duration) (net.Conn, error) {
+	address = strings.TrimPrefix(address, "unix://")
+	return net.DialTimeout("unix", "\x00"+address, timeout)
+}
+
+// NewSocket returns a new socket
+func NewSocket(address string) (*net.UnixListener, error) {
+	if len(address) > 106 {
+		return nil, errors.Errorf("%q: unix socket path too long (> 106)", address)
+	}
+	l, err := net.Listen("unix", "\x00"+address)
+	if err != nil {
+		return nil, errors.Wrapf(err, "failed to listen to abstract unix socket %q", address)
+	}
+	return l.(*net.UnixListener), nil
 }