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// Copyright 2015-2017 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 ns
import (
"fmt"
"os"
"runtime"
"sync"
"syscall"
"golang.org/x/sys/unix"
)
// Returns an object representing the current OS thread's network namespace
func GetCurrentNS() (NetNS, error) {
return GetNS(getCurrentThreadNetNSPath())
}
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())
}
func (ns *netNS) Close() error {
if err := ns.errorIfClosed(); err != nil {
return err
}
if err := ns.file.Close(); err != nil {
return fmt.Errorf("Failed to close %q: %v", ns.file.Name(), err)
}
ns.closed = true
return nil
}
func (ns *netNS) Set() error {
if err := ns.errorIfClosed(); err != nil {
return err
}
if err := unix.Setns(int(ns.Fd()), unix.CLONE_NEWNET); err != nil {
return fmt.Errorf("Error switching to ns %v: %v", ns.file.Name(), err)
}
return nil
}
type NetNS interface {
// Executes the passed closure in this object's network namespace,
// attempting to restore the original namespace before returning.
// However, since each OS thread can have a different network namespace,
// and Go's thread scheduling is highly variable, callers cannot
// guarantee any specific namespace is set unless operations that
// require that namespace are wrapped with Do(). Also, no code called
// from Do() should call runtime.UnlockOSThread(), or the risk
// of executing code in an incorrect namespace will be greater. See
// https://github.com/golang/go/wiki/LockOSThread for further details.
Do(toRun func(NetNS) error) error
// Sets the current network namespace to this object's network namespace.
// Note that since Go's thread scheduling is highly variable, callers
// cannot guarantee the requested namespace will be the current namespace
// after this function is called; to ensure this wrap operations that
// require the namespace with Do() instead.
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
closed bool
}
// netNS implements the NetNS interface
var _ NetNS = &netNS{}
const (
// https://github.com/torvalds/linux/blob/master/include/uapi/linux/magic.h
NSFS_MAGIC = 0x6e736673
PROCFS_MAGIC = 0x9fa0
)
type NSPathNotExistErr struct{ msg string }
func (e NSPathNotExistErr) Error() string { return e.msg }
type NSPathNotNSErr struct{ msg string }
func (e NSPathNotNSErr) Error() string { return e.msg }
func IsNSorErr(nspath string) error {
stat := syscall.Statfs_t{}
if err := syscall.Statfs(nspath, &stat); err != nil {
if os.IsNotExist(err) {
err = NSPathNotExistErr{msg: fmt.Sprintf("failed to Statfs %q: %v", nspath, err)}
} else {
err = fmt.Errorf("failed to Statfs %q: %v", nspath, err)
}
return err
}
switch stat.Type {
case PROCFS_MAGIC, NSFS_MAGIC:
return nil
default:
return NSPathNotNSErr{msg: fmt.Sprintf("unknown FS magic on %q: %x", nspath, stat.Type)}
}
}
// Returns an object representing the namespace referred to by @path
func GetNS(nspath string) (NetNS, error) {
err := IsNSorErr(nspath)
if err != nil {
return nil, err
}
fd, err := os.Open(nspath)
if err != nil {
return nil, err
}
return &netNS{file: fd}, nil
}
func (ns *netNS) Path() string {
return ns.file.Name()
}
func (ns *netNS) Fd() uintptr {
return ns.file.Fd()
}
func (ns *netNS) errorIfClosed() error {
if ns.closed {
return fmt.Errorf("%q has already been closed", ns.file.Name())
}
return nil
}
func (ns *netNS) Do(toRun func(NetNS) error) error {
if err := ns.errorIfClosed(); err != nil {
return err
}
containedCall := func(hostNS NetNS) error {
threadNS, err := GetCurrentNS()
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 network namespace
hostNS, err := GetCurrentNS()
if err != nil {
return fmt.Errorf("Failed to open current namespace: %v", err)
}
defer hostNS.Close()
var wg sync.WaitGroup
wg.Add(1)
var innerError error
go func() {
defer wg.Done()
runtime.LockOSThread()
innerError = containedCall(hostNS)
}()
wg.Wait()
return innerError
}
// 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 err
}
defer ns.Close()
return ns.Do(toRun)
}
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