ns: make namespaces an interface and add NetNS creation capability

This also removes the thread-locking arguments from the ns package
per containernetworking#183 by doing all the namespace
changes in a separate goroutine that locks/unlocks itself, instead of
the caller having to track OS thread locking.

pkg/ip/link.go

@@ -81,7 +81,7 @@ func RandomVethName() (string, error) {
 // SetupVeth sets up a virtual ethernet link.
 // Should be in container netns, and will switch back to hostNS to set the host
 // veth end up.
-func SetupVeth(contVethName string, mtu int, hostNS *os.File) (hostVeth, contVeth netlink.Link, err error) {
+func SetupVeth(contVethName string, mtu int, hostNS ns.NetNS) (hostVeth, contVeth netlink.Link, err error) {
 	var hostVethName string
 	hostVethName, contVeth, err = makeVeth(contVethName, mtu)
 	if err != nil {
@@ -104,10 +104,10 @@ func SetupVeth(contVethName string, mtu int, hostNS *os.File) (hostVeth, contVet
 		return
 	}
 
-	err = ns.WithNetNS(hostNS, false, func(_ *os.File) error {
+	err = hostNS.Do(func(_ ns.NetNS) error {
 		hostVeth, err := netlink.LinkByName(hostVethName)
 		if err != nil {
-			return fmt.Errorf("failed to lookup %q in %q: %v", hostVethName, hostNS.Name(), err)
+			return fmt.Errorf("failed to lookup %q in %q: %v", hostVethName, hostNS.Path(), err)
 		}
 
 		if err = netlink.LinkSetUp(hostVeth); err != nil {

pkg/ns/ns.go

@@ -15,79 +15,195 @@
 package ns
 
 import (
+	"crypto/rand"
 	"fmt"
 	"os"
+	"path"
 	"runtime"
-	"syscall"
+	"sync"
+
+	"golang.org/x/sys/unix"
 )
 
-var setNsMap = map[string]uintptr{
-	"386":   346,
-	"amd64": 308,
-	"arm":   374,
+type NetNS interface {
+	// Executes the passed closure in this object's network namespace,
+	// restoring the original namespace afterwards. If the closure returns
+	// an error, Do attempts to restore the original namespace before
+	// returning.
+	Do(toRun func(NetNS) error) error
+
+	// Sets the current network namespace to this object's network namespace
+	Set() error
+
+	// Returns the filesystem path representing this object's network namespace
+	Path() string
+
+	// Returns a file descriptor representing this object's network namespace
+	Fd() uintptr
+
+	// Cleans up this instance of the network namespace; if this instance
+	// is the last user the namespace will be destroyed
+	Close() error
+}
+
+type netNS struct {
+	file    *os.File
+	mounted bool
 }
 
-// SetNS sets the network namespace on a target file.
-func SetNS(f *os.File, flags uintptr) error {
-	if runtime.GOOS != "linux" {
-		return fmt.Errorf("unsupported OS: %s", runtime.GOOS)
+func getCurrentThreadNetNSPath() string {
+	// /proc/self/ns/net returns the namespace of the main thread, not
+	// of whatever thread this goroutine is running on.  Make sure we
+	// use the thread's net namespace since the thread is switching around
+	return fmt.Sprintf("/proc/%d/task/%d/ns/net", os.Getpid(), unix.Gettid())
+}
+
+// Returns an object representing the namespace referred to by @path
+func GetNS(nspath string) (NetNS, error) {
+	fd, err := os.Open(nspath)
+	if err != nil {
+		return nil, err
+	}
+	return &netNS{file: fd}, nil
+}
+
+// Creates a new network namespace, switches to it, and returns an object
+// representing that network namespace
+func NewNS() (NetNS, error) {
+	const nsRunDir = "/var/run/netns"
+
+	b := make([]byte, 16)
+	_, err := rand.Reader.Read(b)
+	if err != nil {
+		return nil, fmt.Errorf("failed to generate random netns name: %v", err)
 	}
 
-	trap, ok := setNsMap[runtime.GOARCH]
-	if !ok {
-		return fmt.Errorf("unsupported arch: %s", runtime.GOARCH)
+	err = os.MkdirAll(nsRunDir, 0755)
+	if err != nil {
+		return nil, err
 	}
 
-	_, _, err := syscall.RawSyscall(trap, f.Fd(), flags, 0)
-	if err != 0 {
-		return err
+	// create an empty file at the mount point
+	nsName := fmt.Sprintf("cni-%x-%x-%x-%x-%x", b[0:4], b[4:6], b[6:8], b[8:10], b[10:])
+	nsPath := path.Join(nsRunDir, nsName)
+	mountPointFd, err := os.Create(nsPath)
+	if err != nil {
+		return nil, err
 	}
+	mountPointFd.Close()
 
-	return nil
+	// Ensure the mount point is cleaned up on errors; if the namespace
+	// was successfully mounted this will have no effect
+	defer os.RemoveAll(nsPath)
+
+	var wg sync.WaitGroup
+	wg.Add(1)
+
+	// do namespace work in a dedicated goroutine, so that we can safely
+	// Lock/Unlock OSThread without upsetting the lock/unlock state of
+	// the caller of this function
+	var fd *os.File
+	go (func() {
+		defer wg.Done()
+		runtime.LockOSThread()
+
+		// create a new netns on the current thread
+		err = unix.Unshare(unix.CLONE_NEWNET)
+		if err != nil {
+			return
+		}
+
+		// bind mount the new netns from the current thread onto the mount point
+		err = unix.Mount(getCurrentThreadNetNSPath(), nsPath, "none", unix.MS_BIND, "")
+		if err != nil {
+			return
+		}
+
+		fd, err = os.Open(nsPath)
+	})()
+	wg.Wait()
+
+	return &netNS{file: fd, mounted: true}, err
 }
 
-// WithNetNSPath executes the passed closure under the given network
-// namespace, restoring the original namespace afterwards.
-// Changing namespaces must be done on a goroutine that has been
-// locked to an OS thread. If lockThread arg is true, this function
-// locks the goroutine prior to change namespace and unlocks before
-// returning
-func WithNetNSPath(nspath string, lockThread bool, f func(*os.File) error) error {
-	ns, err := os.Open(nspath)
-	if err != nil {
-		return fmt.Errorf("Failed to open %v: %v", nspath, err)
+func (ns *netNS) Path() string {
+	return ns.file.Name()
+}
+
+func (ns *netNS) Fd() uintptr {
+	return ns.file.Fd()
+}
+
+func (ns *netNS) Close() error {
+	ns.file.Close()
+
+	if ns.mounted {
+		if err := unix.Unmount(ns.file.Name(), unix.MNT_DETACH); err != nil {
+			return fmt.Errorf("Failed to unmount namespace %s: %v", ns.file.Name(), err)
+		}
+		if err := os.RemoveAll(ns.file.Name()); err != nil {
+			return fmt.Errorf("Failed to clean up namespace %s: %v", ns.file.Name(), err)
+		}
 	}
-	defer ns.Close()
-	return WithNetNS(ns, lockThread, f)
+	return nil
 }
 
-// WithNetNS executes the passed closure under the given network
-// namespace, restoring the original namespace afterwards.
-// Changing namespaces must be done on a goroutine that has been
-// locked to an OS thread. If lockThread arg is true, this function
-// locks the goroutine prior to change namespace and unlocks before
-// returning.  If the closure returns an error, WithNetNS attempts to
-// restore the original namespace before returning.
-func WithNetNS(ns *os.File, lockThread bool, f func(*os.File) error) error {
-	if lockThread {
-		runtime.LockOSThread()
-		defer runtime.UnlockOSThread()
+func (ns *netNS) Do(toRun func(NetNS) error) error {
+	containedCall := func(hostNS NetNS) error {
+		threadNS, err := GetNS(getCurrentThreadNetNSPath())
+		if err != nil {
+			return fmt.Errorf("failed to open current netns: %v", err)
+		}
+		defer threadNS.Close()
+
+		// switch to target namespace
+		if err = ns.Set(); err != nil {
+			return fmt.Errorf("error switching to ns %v: %v", ns.file.Name(), err)
+		}
+		defer threadNS.Set() // switch back
+
+		return toRun(hostNS)
 	}
-	// save a handle to current (host) network namespace
-	thisNS, err := os.Open("/proc/self/ns/net")
+
+	// save a handle to current network namespace
+	hostNS, err := GetNS(getCurrentThreadNetNSPath())
 	if err != nil {
-		return fmt.Errorf("Failed to open /proc/self/ns/net: %v", err)
+		return fmt.Errorf("Failed to open current namespace: %v", err)
 	}
-	defer thisNS.Close()
+	defer hostNS.Close()
 
-	if err = SetNS(ns, syscall.CLONE_NEWNET); err != nil {
-		return fmt.Errorf("Error switching to ns %v: %v", ns.Name(), err)
-	}
-	defer SetNS(thisNS, syscall.CLONE_NEWNET) // switch back
+	var wg sync.WaitGroup
+	wg.Add(1)
 
-	if err = f(thisNS); err != nil {
-		return err
+	var innerError error
+	go func() {
+		defer wg.Done()
+		runtime.LockOSThread()
+		innerError = containedCall(hostNS)
+	}()
+	wg.Wait()
+
+	return innerError
+}
+
+func (ns *netNS) Set() error {
+	runtime.LockOSThread()
+	defer runtime.UnlockOSThread()
+
+	if _, _, err := unix.Syscall(unix.SYS_SETNS, ns.Fd(), uintptr(unix.CLONE_NEWNET), 0); err != 0 {
+		return fmt.Errorf("Error switching to ns %v: %v", ns.file.Name(), err)
 	}
 
 	return nil
 }
+
+// WithNetNSPath executes the passed closure under the given network
+// namespace, restoring the original namespace afterwards.
+func WithNetNSPath(nspath string, toRun func(NetNS) error) error {
+	ns, err := GetNS(nspath)
+	if err != nil {
+		return fmt.Errorf("Failed to open %v: %v", nspath, err)
+	}
+	defer ns.Close()
+	return ns.Do(toRun)
+}