pkg/ns: remove namespace creation (and move to testutils)

Namespace creation had an unergonomic interface and isn't used, except
for testing code. Remove it; downstream users should really be creating
their own namespaces

pkg/testutils/netns_linux.go

@@ -0,0 +1,157 @@
+// Copyright 2018 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.
+
+package testutils
+
+import (
+	"crypto/rand"
+	"fmt"
+	"os"
+	"path"
+	"runtime"
+	"strings"
+	"sync"
+
+	"github.com/containernetworking/plugins/pkg/ns"
+	"golang.org/x/sys/unix"
+)
+
+const nsRunDir = "/var/run/netns"
+
+// Creates a new persistent (bind-mounted) network namespace and returns an object
+// representing that namespace, without switching to it.
+func NewNS() (ns.NetNS, error) {
+
+	b := make([]byte, 16)
+	_, err := rand.Reader.Read(b)
+	if err != nil {
+		return nil, fmt.Errorf("failed to generate random netns name: %v", err)
+	}
+
+	// Create the directory for mounting network namespaces
+	// This needs to be a shared mountpoint in case it is mounted in to
+	// other namespaces (containers)
+	err = os.MkdirAll(nsRunDir, 0755)
+	if err != nil {
+		return nil, err
+	}
+
+	// Remount the namespace directory shared. This will fail if it is not
+	// already a mountpoint, so bind-mount it on to itself to "upgrade" it
+	// to a mountpoint.
+	err = unix.Mount("", nsRunDir, "none", unix.MS_SHARED|unix.MS_REC, "")
+	if err != nil {
+		if err != unix.EINVAL {
+			return nil, fmt.Errorf("mount --make-rshared %s failed: %q", nsRunDir, err)
+		}
+
+		// Recursively remount /var/run/netns on itself. The recursive flag is
+		// so that any existing netns bindmounts are carried over.
+		err = unix.Mount(nsRunDir, nsRunDir, "none", unix.MS_BIND|unix.MS_REC, "")
+		if err != nil {
+			return nil, fmt.Errorf("mount --rbind %s %s failed: %q", nsRunDir, nsRunDir, err)
+		}
+
+		// Now we can make it shared
+		err = unix.Mount("", nsRunDir, "none", unix.MS_SHARED|unix.MS_REC, "")
+		if err != nil {
+			return nil, fmt.Errorf("mount --make-rshared %s failed: %q", nsRunDir, err)
+		}
+
+	}
+
+	nsName := fmt.Sprintf("cnitest-%x-%x-%x-%x-%x", b[0:4], b[4:6], b[6:8], b[8:10], b[10:])
+
+	// create an empty file at the mount point
+	nsPath := path.Join(nsRunDir, nsName)
+	mountPointFd, err := os.Create(nsPath)
+	if err != nil {
+		return nil, err
+	}
+	mountPointFd.Close()
+
+	// Ensure the mount point is cleaned up on errors; if the namespace
+	// was successfully mounted this will have no effect because the file
+	// is in-use
+	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
+	go (func() {
+		defer wg.Done()
+		runtime.LockOSThread()
+		// Don't unlock. By not unlocking, golang will kill the OS thread when the
+		// goroutine is done (for go1.10+)
+
+		var origNS ns.NetNS
+		origNS, err = ns.GetNS(getCurrentThreadNetNSPath())
+		if err != nil {
+			return
+		}
+		defer origNS.Close()
+
+		// create a new netns on the current thread
+		err = unix.Unshare(unix.CLONE_NEWNET)
+		if err != nil {
+			return
+		}
+
+		// Put this thread back to the orig ns, since it might get reused (pre go1.10)
+		defer origNS.Set()
+
+		// bind mount the netns from the current thread (from /proc) onto the
+		// mount point. This causes the namespace to persist, even when there
+		// are no threads in the ns.
+		err = unix.Mount(getCurrentThreadNetNSPath(), nsPath, "none", unix.MS_BIND, "")
+		if err != nil {
+			err = fmt.Errorf("failed to bind mount ns at %s: %v", nsPath, err)
+		}
+	})()
+	wg.Wait()
+
+	if err != nil {
+		return nil, fmt.Errorf("failed to create namespace: %v", err)
+	}
+
+	return ns.GetNS(nsPath)
+}
+
+// UnmountNS unmounts the NS held by the netns object
+func UnmountNS(ns ns.NetNS) error {
+	nsPath := ns.Path()
+	// Only unmount if it's been bind-mounted (don't touch namespaces in /proc...)
+	if strings.HasPrefix(nsPath, nsRunDir) {
+		if err := unix.Unmount(nsPath, 0); err != nil {
+			return fmt.Errorf("failed to unmount NS: at %s: %v", nsPath, err)
+		}
+
+		if err := os.Remove(nsPath); err != nil {
+			return fmt.Errorf("failed to remove ns path %s: %v", nsPath, err)
+		}
+	}
+
+	return nil
+}
+
+// getCurrentThreadNetNSPath copied from pkg/ns
+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())
+}