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Vishvananda Ishaya 2014-08-31 13:47:35 -07:00
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Copyright 2014 Vishvananda Ishaya.
Copyright 2014 Docker, Inc.
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# netns - network namespaces in go #
The netns package provides an ultra-simple interface for handling
network namespaces in go. Changing namespaces requires elevated
privileges, so in most cases this code needs to be run as root.
## Local Build and Test ##
You can use go get command:
go get github.com/vishvananda/netns
Testing (requires root):
sudo -E go test github.com/vishvananda/netns
## Example ##
```go
package main
import (
"net"
"runtime"
"github.com/vishvananada/netns"
)
func main() {
// Lock the OS Thread so we don't accidentally switch namespaces
runtime.LockOSThread()
defer runtime.UnlockOSThread()
// Save the current network namespace
origns, _ := netns.Get()
defer origns.Close()
// Create a new network namespace
newns, _ := netns.New()
defer newns.Close()
// Do something with tne network namespace
ifaces, _ := net.Interfaces()
fmt.Printf("Interfaces: %v\n", ifaces)
// Switch back to the original namespace
netns.Set(origns)
}
```

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// Package netns allows ultra-simple network namespace handling. NsHandles
// can be retrieved and set. Note that the current namespace is thread
// local so actions that set and reset namespaces should use LockOSThread
// to make sure the namespace doesn't change due to a goroutine switch.
// It is best to close NsHandles when you are done with them. This can be
// accomplished via a `defer ns.Close()` on the handle. Changing namespaces
// requires elevated privileges, so in most cases this code needs to be run
// as root.
package netns
import (
"fmt"
"io/ioutil"
"os"
"path/filepath"
"strconv"
"strings"
"syscall"
)
const (
// These constants belong in the syscall library but have not been
// added yet.
CLONE_NEWUTS = 0x04000000 /* New utsname group? */
CLONE_NEWIPC = 0x08000000 /* New ipcs */
CLONE_NEWUSER = 0x10000000 /* New user namespace */
CLONE_NEWPID = 0x20000000 /* New pid namespace */
CLONE_NEWNET = 0x40000000 /* New network namespace */
CLONE_IO = 0x80000000 /* Get io context */
)
// Setns sets namespace using syscall. Note that this should be a method
// in syscall but it has not been added.
func Setns(ns NsHandle, nstype int) (err error) {
_, _, e1 := syscall.Syscall(SYS_SETNS, uintptr(ns), uintptr(nstype), 0)
if e1 != 0 {
err = e1
}
return
}
// NsHandle is a handle to a network namespace. It can be cast directly
// to an int and used as a file descriptor.
type NsHandle int
// Equal determines if two network handles refer to the same network
// namespace. This is done by comparing the device and inode that the
// file descripors point to.
func (ns NsHandle) Equal(other NsHandle) bool {
var s1, s2 syscall.Stat_t
if err := syscall.Fstat(int(ns), &s1); err != nil {
return false
}
if err := syscall.Fstat(int(other), &s2); err != nil {
return false
}
return (s1.Dev == s2.Dev) && (s1.Ino == s2.Ino)
}
// String shows the file descriptor number and its dev and inode.
func (ns NsHandle) String() string {
var s syscall.Stat_t
if err := syscall.Fstat(int(ns), &s); err != nil {
return fmt.Sprintf("NS(%d: unknown)", ns)
}
return fmt.Sprintf("NS(%d: %d, %d)", ns, s.Dev, s.Ino)
}
// IsOpen returns true if Close() has not been called.
func (ns NsHandle) IsOpen() bool {
return ns != -1
}
// Close closes the NsHandle and resets its file descriptor to -1.
// It is not safe to use an NsHandle after Close() is called.
func (ns *NsHandle) Close() error {
if err := syscall.Close(int(*ns)); err != nil {
return err
}
(*ns) = -1
return nil
}
// Set sets the current network namespace to the namespace represented
// by NsHandle.
func Set(ns NsHandle) (err error) {
return Setns(ns, CLONE_NEWNET)
}
// New creates a new network namespace and returns a handle to it.
func New() (ns NsHandle, err error) {
if err := syscall.Unshare(CLONE_NEWNET); err != nil {
return -1, err
}
return Get()
}
// Get gets a handle to the current threads network namespace.
func Get() (NsHandle, error) {
return GetFromPid(os.Getpid())
}
// GetFromName gets a handle to a named network namespace such as one
// created by `ip netns add`.
func GetFromName(name string) (NsHandle, error) {
fd, err := syscall.Open(fmt.Sprintf("/var/run/netns/%s", name), syscall.O_RDONLY, 0)
if err != nil {
return -1, err
}
return NsHandle(fd), nil
}
// GetFromName gets a handle to the network namespace of a given pid.
func GetFromPid(pid int) (NsHandle, error) {
fd, err := syscall.Open(fmt.Sprintf("/proc/%d/ns/net", pid), syscall.O_RDONLY, 0)
if err != nil {
return -1, err
}
return NsHandle(fd), nil
}
// GetFromName gets a handle to the network namespace of a docker container.
// Id is prefixed matched against the running docker containers, so a short
// identifier can be used as long as it isn't ambiguous.
func GetFromDocker(id string) (NsHandle, error) {
pid, err := getPidForContainer(id)
if err != nil {
return -1, err
}
return GetFromPid(pid)
}
// borrowed from docker/utils/utils.go
func findCgroupMountpoint(cgroupType string) (string, error) {
output, err := ioutil.ReadFile("/proc/mounts")
if err != nil {
return "", err
}
// /proc/mounts has 6 fields per line, one mount per line, e.g.
// cgroup /sys/fs/cgroup/devices cgroup rw,relatime,devices 0 0
for _, line := range strings.Split(string(output), "\n") {
parts := strings.Split(line, " ")
if len(parts) == 6 && parts[2] == "cgroup" {
for _, opt := range strings.Split(parts[3], ",") {
if opt == cgroupType {
return parts[1], nil
}
}
}
}
return "", fmt.Errorf("cgroup mountpoint not found for %s", cgroupType)
}
// Returns the relative path to the cgroup docker is running in.
// borrowed from docker/utils/utils.go
// modified to get the docker pid instead of using /proc/self
func getThisCgroup(cgroupType string) (string, error) {
dockerpid, err := ioutil.ReadFile("/var/run/docker.pid")
if err != nil {
return "", err
}
result := strings.Split(string(dockerpid), "\n")
if len(result) == 0 || len(result[0]) == 0 {
return "", fmt.Errorf("docker pid not found in /var/run/docker.pid")
}
pid, err := strconv.Atoi(result[0])
output, err := ioutil.ReadFile(fmt.Sprintf("/proc/%d/cgroup", pid))
if err != nil {
return "", err
}
for _, line := range strings.Split(string(output), "\n") {
parts := strings.Split(line, ":")
// any type used by docker should work
if parts[1] == cgroupType {
return parts[2], nil
}
}
return "", fmt.Errorf("cgroup '%s' not found in /proc/%d/cgroup", cgroupType, pid)
}
// Returns the first pid in a container.
// borrowed from docker/utils/utils.go
// modified to only return the first pid
// modified to glob with id
func getPidForContainer(id string) (int, error) {
pid := 0
// memory is chosen randomly, any cgroup used by docker works
cgroupType := "memory"
cgroupRoot, err := findCgroupMountpoint(cgroupType)
if err != nil {
return pid, err
}
cgroupThis, err := getThisCgroup(cgroupType)
if err != nil {
return pid, err
}
id += "*"
filename := filepath.Join(cgroupRoot, cgroupThis, id, "tasks")
filenames, _ := filepath.Glob(filename)
if len(filenames) > 1 {
return pid, fmt.Errorf("Ambiguous id supplied: %v", filenames)
} else if len(filenames) == 1 {
filename = filenames[0]
}
if _, err := os.Stat(filename); os.IsNotExist(err) {
// With more recent lxc versions use, cgroup will be in lxc/
filename = filepath.Join(cgroupRoot, cgroupThis, "lxc", id, "tasks")
filenames, _ = filepath.Glob(filename)
if len(filenames) > 1 {
return pid, fmt.Errorf("Ambiguous id supplied: %v", filenames)
} else if len(filenames) == 1 {
filename = filenames[0]
} else {
return pid, fmt.Errorf("Unable to find container: %v", id[:len(id)-1])
}
}
output, err := ioutil.ReadFile(filename)
if err != nil {
return pid, err
}
result := strings.Split(string(output), "\n")
if len(result) == 0 || len(result[0]) == 0 {
return pid, fmt.Errorf("No pid found for container")
}
pid, err = strconv.Atoi(result[0])
if err != nil {
return pid, fmt.Errorf("Invalid pid '%s': %s", result[0], err)
}
return pid, nil
}

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package netns
const (
SYS_SETNS = 346
)

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package netns
const (
SYS_SETNS = 308
)

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package netns
const (
SYS_SETNS = 374
)

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package netns
import (
"runtime"
"testing"
)
func TestGetNewSetDelete(t *testing.T) {
runtime.LockOSThread()
defer runtime.UnlockOSThread()
origns, err := Get()
if err != nil {
t.Fatal(err)
}
newns, err := New()
if err != nil {
t.Fatal(err)
}
if origns.Equal(newns) {
t.Fatal("New ns failed")
}
if err := Set(origns); err != nil {
t.Fatal(err)
}
newns.Close()
if newns.IsOpen() {
t.Fatal("newns still open after close", newns)
}
ns, err := Get()
if err != nil {
t.Fatal(err)
}
if !ns.Equal(origns) {
t.Fatal("Reset ns failed", origns, newns, ns)
}
}

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// +build !linux
package netns
import (
"errors"
)
var (
ErrNotImplemented = errors.New("not implemented")
)
func Set(ns Namespace) (err error) {
return ErrNotImplemented
}
func New() (ns Namespace, err error) {
return -1, ErrNotImplemented
}
func Get() (Namespace, error) {
return -1, ErrNotImplemented
}
func GetFromName(name string) (Namespace, error) {
return -1, ErrNotImplemented
}
func GetFromPid(pid int) (Namespace, error) {
return -1, ErrNotImplemented
}
func GetFromDocker(id string) (Namespace, error) {
return -1, ErrNotImplemented
}