Merge pull request #27405 from tonistiigi/fix-fifo2

Fix issues with fifos blocking on open

hack/vendor.sh

@@ -144,6 +144,7 @@ clone git github.com/docker/docker-credential-helpers v0.3.0
 
 # containerd
 clone git github.com/docker/containerd 52ef1ceb4b660c42cf4ea9013180a5663968d4c7
+clone git github.com/tonistiigi/fifo 8c56881ce5e63e19e2dfc495c8af0fb90916467d
 
 # cluster
 clone git github.com/docker/swarmkit 3b221eb0391d34ae0b9dac65df02b5b64de6dff2

libcontainerd/client_linux.go

@@ -13,6 +13,7 @@ import (
 	"github.com/Sirupsen/logrus"
 	containerd "github.com/docker/containerd/api/grpc/types"
 	"github.com/docker/docker/pkg/idtools"
+	"github.com/docker/docker/pkg/ioutils"
 	"github.com/docker/docker/pkg/mount"
 	"github.com/golang/protobuf/ptypes"
 	"github.com/golang/protobuf/ptypes/timestamp"
@@ -100,12 +101,26 @@ func (clnt *client) AddProcess(ctx context.Context, containerID, processFriendly
 		return -1, err
 	}
 
+	var stdinOnce sync.Once
+	stdin := iopipe.Stdin
+	iopipe.Stdin = ioutils.NewWriteCloserWrapper(stdin, func() error {
+		var err error
+		stdinOnce.Do(func() { // on error from attach we don't know if stdin was already closed
+			err = stdin.Close()
+			if err2 := p.sendCloseStdin(); err == nil {
+				err = err2
+			}
+		})
+		return err
+	})
+
 	container.processes[processFriendlyName] = p
 
 	clnt.unlock(containerID)
 
 	if err := clnt.backend.AttachStreams(processFriendlyName, *iopipe); err != nil {
 		clnt.lock(containerID)
+		p.closeFifos(iopipe)
 		return -1, err
 	}
 	clnt.lock(containerID)
@@ -420,8 +435,18 @@ func (clnt *client) restore(cont *containerd.Container, lastEvent *containerd.Ev
 	if err != nil {
 		return err
 	}
+	var stdinOnce sync.Once
+	stdin := iopipe.Stdin
+	iopipe.Stdin = ioutils.NewWriteCloserWrapper(stdin, func() error {
+		var err error
+		stdinOnce.Do(func() { // on error from attach we don't know if stdin was already closed
+			err = stdin.Close()
+		})
+		return err
+	})
 
 	if err := clnt.backend.AttachStreams(containerID, *iopipe); err != nil {
+		container.closeFifos(iopipe)
 		return err
 	}
 
@@ -434,6 +459,7 @@ func (clnt *client) restore(cont *containerd.Container, lastEvent *containerd.Ev
 		}})
 
 	if err != nil {
+		container.closeFifos(iopipe)
 		return err
 	}
 

libcontainerd/client_windows.go

@@ -4,6 +4,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"io/ioutil"
 	"os"
 	"path/filepath"
 	"strings"
@@ -322,10 +323,10 @@ func (clnt *client) AddProcess(ctx context.Context, containerID, processFriendly
 
 	// Convert io.ReadClosers to io.Readers
 	if stdout != nil {
-		iopipe.Stdout = openReaderFromPipe(stdout)
+		iopipe.Stdout = ioutil.NopCloser(&autoClosingReader{ReadCloser: stdout})
 	}
 	if stderr != nil {
-		iopipe.Stderr = openReaderFromPipe(stderr)
+		iopipe.Stderr = ioutil.NopCloser(&autoClosingReader{ReadCloser: stderr})
 	}
 
 	proc := &process{

libcontainerd/container_linux.go

@@ -6,12 +6,15 @@ import (
 	"io/ioutil"
 	"os"
 	"path/filepath"
+	"sync"
 	"syscall"
+	"time"
 
 	"github.com/Sirupsen/logrus"
 	containerd "github.com/docker/containerd/api/grpc/types"
 	"github.com/docker/docker/pkg/ioutils"
 	"github.com/opencontainers/runtime-spec/specs-go"
+	"github.com/tonistiigi/fifo"
 	"golang.org/x/net/context"
 )
 
@@ -90,22 +93,37 @@ func (ctr *container) start(checkpoint string, checkpointDir string) error {
 	if err != nil {
 		return nil
 	}
-	createChan := make(chan struct{})
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	ready := make(chan struct{})
+
 	iopipe, err := ctr.openFifos(spec.Process.Terminal)
 	if err != nil {
 		return err
 	}
 
+	var stdinOnce sync.Once
+
 	// we need to delay stdin closure after container start or else "stdin close"
 	// event will be rejected by containerd.
 	// stdin closure happens in AttachStreams
 	stdin := iopipe.Stdin
 	iopipe.Stdin = ioutils.NewWriteCloserWrapper(stdin, func() error {
-		go func() {
-			<-createChan
-			stdin.Close()
-		}()
-		return nil
+		var err error
+		stdinOnce.Do(func() { // on error from attach we don't know if stdin was already closed
+			err = stdin.Close()
+			go func() {
+				select {
+				case <-ready:
+					if err := ctr.sendCloseStdin(); err != nil {
+						logrus.Warnf("failed to close stdin: %+v")
+					}
+				case <-ctx.Done():
+				}
+			}()
+		})
+		return err
 	})
 
 	r := &containerd.CreateContainerRequest{
@@ -124,19 +142,17 @@ func (ctr *container) start(checkpoint string, checkpointDir string) error {
 	ctr.client.appendContainer(ctr)
 
 	if err := ctr.client.backend.AttachStreams(ctr.containerID, *iopipe); err != nil {
-		close(createChan)
 		ctr.closeFifos(iopipe)
 		return err
 	}
 
 	resp, err := ctr.client.remote.apiClient.CreateContainer(context.Background(), r)
 	if err != nil {
-		close(createChan)
 		ctr.closeFifos(iopipe)
 		return err
 	}
 	ctr.systemPid = systemPid(resp.Container)
-	close(createChan)
+	close(ready)
 
 	return ctr.client.backend.StateChanged(ctr.containerID, StateInfo{
 		CommonStateInfo: CommonStateInfo{
@@ -207,15 +223,15 @@ func (ctr *container) handleEvent(e *containerd.Event) error {
 // discardFifos attempts to fully read the container fifos to unblock processes
 // that may be blocked on the writer side.
 func (ctr *container) discardFifos() {
+	ctx, _ := context.WithTimeout(context.Background(), 3*time.Second)
 	for _, i := range []int{syscall.Stdout, syscall.Stderr} {
-		f := ctr.fifo(i)
-		c := make(chan struct{})
+		f, err := fifo.OpenFifo(ctx, ctr.fifo(i), syscall.O_RDONLY|syscall.O_NONBLOCK, 0)
+		if err != nil {
+			logrus.Warnf("error opening fifo %v for discarding: %+v", f, err)
+			continue
+		}
 		go func() {
-			r := openReaderFromFifo(f)
-			close(c) // this channel is used to not close the writer too early, before readonly open has been called.
-			io.Copy(ioutil.Discard, r)
+			io.Copy(ioutil.Discard, f)
 		}()
-		<-c
-		closeReaderFifo(f) // avoid blocking permanently on open if there is no writer side
 	}
 }

libcontainerd/container_windows.go

@@ -3,6 +3,7 @@ package libcontainerd
 import (
 	"fmt"
 	"io"
+	"io/ioutil"
 	"strings"
 	"syscall"
 	"time"
@@ -131,10 +132,10 @@ func (ctr *container) start() error {
 
 	// Convert io.ReadClosers to io.Readers
 	if stdout != nil {
-		iopipe.Stdout = openReaderFromPipe(stdout)
+		iopipe.Stdout = ioutil.NopCloser(&autoClosingReader{ReadCloser: stdout})
 	}
 	if stderr != nil {
-		iopipe.Stderr = openReaderFromPipe(stderr)
+		iopipe.Stderr = ioutil.NopCloser(&autoClosingReader{ReadCloser: stderr})
 	}
 
 	// Save the PID

libcontainerd/process_linux.go

@@ -1,14 +1,15 @@
 package libcontainerd
 
 import (
-	"fmt"
 	"io"
+	"io/ioutil"
 	"os"
 	"path/filepath"
 	"syscall"
+	"time"
 
 	containerd "github.com/docker/containerd/api/grpc/types"
-	"github.com/docker/docker/pkg/ioutils"
+	"github.com/tonistiigi/fifo"
 	"golang.org/x/net/context"
 )
 
@@ -26,49 +27,67 @@ type process struct {
 	dir string
 }
 
-func (p *process) openFifos(terminal bool) (*IOPipe, error) {
-	bundleDir := p.dir
-	if err := os.MkdirAll(bundleDir, 0700); err != nil {
+func (p *process) openFifos(terminal bool) (pipe *IOPipe, err error) {
+	if err := os.MkdirAll(p.dir, 0700); err != nil {
 		return nil, err
 	}
 
-	for i := 0; i < 3; i++ {
-		f := p.fifo(i)
-		if err := syscall.Mkfifo(f, 0700); err != nil && !os.IsExist(err) {
-			return nil, fmt.Errorf("mkfifo: %s %v", f, err)
-		}
-	}
+	ctx, _ := context.WithTimeout(context.Background(), 15*time.Second)
 
 	io := &IOPipe{}
-	stdinf, err := os.OpenFile(p.fifo(syscall.Stdin), syscall.O_RDWR, 0)
+
+	io.Stdin, err = fifo.OpenFifo(ctx, p.fifo(syscall.Stdin), syscall.O_WRONLY|syscall.O_CREAT|syscall.O_NONBLOCK, 0700)
+	if err != nil {
+		return nil, err
+	}
+
+	defer func() {
+		if err != nil {
+			io.Stdin.Close()
+		}
+	}()
+
+	io.Stdout, err = fifo.OpenFifo(ctx, p.fifo(syscall.Stdout), syscall.O_RDONLY|syscall.O_CREAT|syscall.O_NONBLOCK, 0700)
 	if err != nil {
 		return nil, err
 	}
 
-	io.Stdout = openReaderFromFifo(p.fifo(syscall.Stdout))
+	defer func() {
+		if err != nil {
+			io.Stdout.Close()
+		}
+	}()
+
 	if !terminal {
-		io.Stderr = openReaderFromFifo(p.fifo(syscall.Stderr))
+		io.Stderr, err = fifo.OpenFifo(ctx, p.fifo(syscall.Stderr), syscall.O_RDONLY|syscall.O_CREAT|syscall.O_NONBLOCK, 0700)
+		if err != nil {
+			return nil, err
+		}
+		defer func() {
+			if err != nil {
+				io.Stderr.Close()
+			}
+		}()
 	} else {
-		io.Stderr = emptyReader{}
+		io.Stderr = ioutil.NopCloser(emptyReader{})
 	}
 
-	io.Stdin = ioutils.NewWriteCloserWrapper(stdinf, func() error {
-		stdinf.Close()
-		_, err := p.client.remote.apiClient.UpdateProcess(context.Background(), &containerd.UpdateProcessRequest{
-			Id:         p.containerID,
-			Pid:        p.friendlyName,
-			CloseStdin: true,
-		})
-		return err
-	})
-
 	return io, nil
 }
 
+func (p *process) sendCloseStdin() error {
+	_, err := p.client.remote.apiClient.UpdateProcess(context.Background(), &containerd.UpdateProcessRequest{
+		Id:         p.containerID,
+		Pid:        p.friendlyName,
+		CloseStdin: true,
+	})
+	return err
+}
+
 func (p *process) closeFifos(io *IOPipe) {
 	io.Stdin.Close()
-	closeReaderFifo(p.fifo(syscall.Stdout))
-	closeReaderFifo(p.fifo(syscall.Stderr))
+	io.Stdout.Close()
+	io.Stderr.Close()
 }
 
 type emptyReader struct{}
@@ -77,34 +96,6 @@ func (r emptyReader) Read(b []byte) (int, error) {
 	return 0, io.EOF
 }
 
-func openReaderFromFifo(fn string) io.Reader {
-	r, w := io.Pipe()
-	c := make(chan struct{})
-	go func() {
-		close(c)
-		stdoutf, err := os.OpenFile(fn, syscall.O_RDONLY, 0)
-		if err != nil {
-			r.CloseWithError(err)
-		}
-		if _, err := io.Copy(w, stdoutf); err != nil {
-			r.CloseWithError(err)
-		}
-		w.Close()
-		stdoutf.Close()
-	}()
-	<-c // wait for the goroutine to get scheduled and syscall to block
-	return r
-}
-
-// closeReaderFifo closes fifo that may be blocked on open by opening the write side.
-func closeReaderFifo(fn string) {
-	f, err := os.OpenFile(fn, syscall.O_WRONLY|syscall.O_NONBLOCK, 0)
-	if err != nil {
-		return
-	}
-	f.Close()
-}
-
 func (p *process) fifo(index int) string {
 	return filepath.Join(p.dir, p.friendlyName+"-"+fdNames[index])
 }

libcontainerd/process_windows.go

@@ -2,6 +2,7 @@ package libcontainerd
 
 import (
 	"io"
+	"sync"
 
 	"github.com/Microsoft/hcsshim"
 	"github.com/docker/docker/pkg/ioutils"
@@ -18,16 +19,17 @@ type process struct {
 	hcsProcess  hcsshim.Process
 }
 
-func openReaderFromPipe(p io.ReadCloser) io.Reader {
-	r, w := io.Pipe()
-	go func() {
-		if _, err := io.Copy(w, p); err != nil {
-			r.CloseWithError(err)
-		}
-		w.Close()
-		p.Close()
-	}()
-	return r
+type autoClosingReader struct {
+	io.ReadCloser
+	sync.Once
+}
+
+func (r *autoClosingReader) Read(b []byte) (n int, err error) {
+	n, err = r.ReadCloser.Read(b)
+	if err == io.EOF {
+		r.Once.Do(func() { r.ReadCloser.Close() })
+	}
+	return
 }
 
 func createStdInCloser(pipe io.WriteCloser, process hcsshim.Process) io.WriteCloser {

libcontainerd/types.go

@@ -61,7 +61,7 @@ type CreateOption interface {
 // IOPipe contains the stdio streams.
 type IOPipe struct {
 	Stdin    io.WriteCloser
-	Stdout   io.Reader
-	Stderr   io.Reader
+	Stdout   io.ReadCloser
+	Stderr   io.ReadCloser
 	Terminal bool // Whether stderr is connected on Windows
 }

vendor/src/github.com/tonistiigi/fifo/LICENSE

@@ -0,0 +1,21 @@
+MIT
+
+Copyright (C) 2016 Tõnis Tiigi <tonistiigi@gmail.com>
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.

vendor/src/github.com/tonistiigi/fifo/Makefile

@@ -0,0 +1,13 @@
+.PHONY: fmt vet test deps
+
+test: deps
+	go test -v ./...
+
+deps:
+	go get -d -t ./...
+
+fmt:
+	gofmt -s -l .
+
+vet:
+	go vet ./...

vendor/src/github.com/tonistiigi/fifo/fifo.go

@@ -0,0 +1,215 @@
+package fifo
+
+import (
+	"context"
+	"io"
+	"os"
+	"runtime"
+	"sync"
+	"syscall"
+
+	"github.com/pkg/errors"
+)
+
+type fifo struct {
+	flag        int
+	opened      chan struct{}
+	closed      chan struct{}
+	closing     chan struct{}
+	err         error
+	file        *os.File
+	closingOnce sync.Once // close has been called
+	closedOnce  sync.Once // fifo is closed
+	handle      *handle
+}
+
+var leakCheckWg *sync.WaitGroup
+
+// OpenFifo opens a fifo. Returns io.ReadWriteCloser.
+// Context can be used to cancel this function until open(2) has not returned.
+// Accepted flags:
+// - syscall.O_CREAT - create new fifo if one doesn't exist
+// - syscall.O_RDONLY - open fifo only from reader side
+// - syscall.O_WRONLY - open fifo only from writer side
+// - syscall.O_RDWR - open fifo from both sides, never block on syscall level
+// - syscall.O_NONBLOCK - return io.ReadWriteCloser even if other side of the
+//     fifo isn't open. read/write will be connected after the actual fifo is
+//     open or after fifo is closed.
+func OpenFifo(ctx context.Context, fn string, flag int, perm os.FileMode) (io.ReadWriteCloser, error) {
+	if _, err := os.Stat(fn); err != nil {
+		if os.IsNotExist(err) && flag&syscall.O_CREAT != 0 {
+			if err := syscall.Mkfifo(fn, uint32(perm&os.ModePerm)); err != nil && !os.IsExist(err) {
+				return nil, errors.Wrapf(err, "error creating fifo %v", fn)
+			}
+		} else {
+			return nil, err
+		}
+	}
+
+	block := flag&syscall.O_NONBLOCK == 0 || flag&syscall.O_RDWR != 0
+
+	flag &= ^syscall.O_CREAT
+	flag &= ^syscall.O_NONBLOCK
+
+	h, err := getHandle(fn)
+	if err != nil {
+		return nil, err
+	}
+
+	f := &fifo{
+		handle:  h,
+		flag:    flag,
+		opened:  make(chan struct{}),
+		closed:  make(chan struct{}),
+		closing: make(chan struct{}),
+	}
+
+	wg := leakCheckWg
+	if wg != nil {
+		wg.Add(2)
+	}
+
+	go func() {
+		if wg != nil {
+			defer wg.Done()
+		}
+		select {
+		case <-ctx.Done():
+			f.Close()
+		case <-f.opened:
+		case <-f.closed:
+		}
+	}()
+	go func() {
+		if wg != nil {
+			defer wg.Done()
+		}
+		var file *os.File
+		fn, err := h.Path()
+		if err == nil {
+			file, err = os.OpenFile(fn, flag, 0)
+		}
+		select {
+		case <-f.closing:
+			if err == nil {
+				select {
+				case <-ctx.Done():
+					err = ctx.Err()
+				default:
+					err = errors.Errorf("fifo %v was closed before opening", fn)
+				}
+				if file != nil {
+					file.Close()
+				}
+			}
+		default:
+		}
+		if err != nil {
+			f.closedOnce.Do(func() {
+				f.err = err
+				close(f.closed)
+			})
+			return
+		}
+		f.file = file
+		close(f.opened)
+	}()
+	if block {
+		select {
+		case <-f.opened:
+		case <-f.closed:
+			return nil, f.err
+		}
+	}
+	return f, nil
+}
+
+// Read from a fifo to a byte array.
+func (f *fifo) Read(b []byte) (int, error) {
+	if f.flag&syscall.O_WRONLY > 0 {
+		return 0, errors.New("reading from write-only fifo")
+	}
+	select {
+	case <-f.opened:
+		return f.file.Read(b)
+	default:
+	}
+	select {
+	case <-f.opened:
+		return f.file.Read(b)
+	case <-f.closed:
+		return 0, errors.New("reading from a closed fifo")
+	}
+}
+
+// Write from byte array to a fifo.
+func (f *fifo) Write(b []byte) (int, error) {
+	if f.flag&(syscall.O_WRONLY|syscall.O_RDWR) == 0 {
+		return 0, errors.New("writing to read-only fifo")
+	}
+	select {
+	case <-f.opened:
+		return f.file.Write(b)
+	default:
+	}
+	select {
+	case <-f.opened:
+		return f.file.Write(b)
+	case <-f.closed:
+		return 0, errors.New("writing to a closed fifo")
+	}
+}
+
+// Close the fifo. Next reads/writes will error. This method can also be used
+// before open(2) has returned and fifo was never opened.
+func (f *fifo) Close() error {
+	for {
+		select {
+		case <-f.closed:
+			f.handle.Close()
+			return f.err
+		default:
+			select {
+			case <-f.opened:
+				f.closedOnce.Do(func() {
+					f.err = f.file.Close()
+					close(f.closed)
+				})
+			default:
+				if f.flag&syscall.O_RDWR != 0 {
+					runtime.Gosched()
+					break
+				}
+				f.closingOnce.Do(func() {
+					close(f.closing)
+				})
+				reverseMode := syscall.O_WRONLY
+				if f.flag&syscall.O_WRONLY > 0 {
+					reverseMode = syscall.O_RDONLY
+				}
+				fn, err := f.handle.Path()
+				// if Close() is called concurrently(shouldn't) it may cause error
+				// because handle is closed
+				select {
+				case <-f.closed:
+				default:
+					if err != nil {
+						// Path has become invalid. We will leak a goroutine.
+						// This case should not happen in linux.
+						f.closedOnce.Do(func() {
+							f.err = err
+							close(f.closed)
+						})
+						<-f.closed
+						break
+					}
+					f, err := os.OpenFile(fn, reverseMode|syscall.O_NONBLOCK, 0)
+					if err == nil {
+						f.Close()
+					}
+					runtime.Gosched()
+				}
+			}
+		}
+	}
+}

vendor/src/github.com/tonistiigi/fifo/handle_linux.go

@@ -0,0 +1,70 @@
+// +build linux
+
+package fifo
+
+import (
+	"fmt"
+	"os"
+	"sync"
+	"syscall"
+
+	"github.com/pkg/errors"
+)
+
+const O_PATH = 010000000
+
+type handle struct {
+	f         *os.File
+	dev       uint64
+	ino       uint64
+	closeOnce sync.Once
+}
+
+func getHandle(fn string) (*handle, error) {
+	f, err := os.OpenFile(fn, O_PATH, 0)
+	if err != nil {
+		return nil, errors.Wrapf(err, "failed to open %v with O_PATH", fn)
+	}
+
+	var stat syscall.Stat_t
+	if err := syscall.Fstat(int(f.Fd()), &stat); err != nil {
+		f.Close()
+		return nil, errors.Wrapf(err, "failed to stat handle %v", f.Fd())
+	}
+
+	h := &handle{
+		f:   f,
+		dev: stat.Dev,
+		ino: stat.Ino,
+	}
+
+	// check /proc just in case
+	if _, err := os.Stat(h.procPath()); err != nil {
+		f.Close()
+		return nil, errors.Wrapf(err, "couldn't stat %v", h.procPath())
+	}
+
+	return h, nil
+}
+
+func (h *handle) procPath() string {
+	return fmt.Sprintf("/proc/self/fd/%d", h.f.Fd())
+}
+
+func (h *handle) Path() (string, error) {
+	var stat syscall.Stat_t
+	if err := syscall.Stat(h.procPath(), &stat); err != nil {
+		return "", errors.Wrapf(err, "path %v could not be statted", h.procPath())
+	}
+	if stat.Dev != h.dev || stat.Ino != h.ino {
+		return "", errors.Errorf("failed to verify handle %v/%v %v/%v", stat.Dev, h.dev, stat.Ino, h.ino)
+	}
+	return h.procPath(), nil
+}
+
+func (h *handle) Close() error {
+	h.closeOnce.Do(func() {
+		h.f.Close()
+	})
+	return nil
+}

vendor/src/github.com/tonistiigi/fifo/handle_nolinux.go

@@ -0,0 +1,45 @@
+// +build !linux
+
+package fifo
+
+import (
+	"syscall"
+
+	"github.com/pkg/errors"
+)
+
+type handle struct {
+	fn  string
+	dev uint64
+	ino uint64
+}
+
+func getHandle(fn string) (*handle, error) {
+	var stat syscall.Stat_t
+	if err := syscall.Stat(fn, &stat); err != nil {
+		return nil, errors.Wrapf(err, "failed to stat %v", fn)
+	}
+
+	h := &handle{
+		fn:  fn,
+		dev: uint64(stat.Dev),
+		ino: stat.Ino,
+	}
+
+	return h, nil
+}
+
+func (h *handle) Path() (string, error) {
+	var stat syscall.Stat_t
+	if err := syscall.Stat(h.fn, &stat); err != nil {
+		return "", errors.Wrapf(err, "path %v could not be statted", h.fn)
+	}
+	if uint64(stat.Dev) != h.dev || stat.Ino != h.ino {
+		return "", errors.Errorf("failed to verify handle %v/%v %v/%v", stat.Dev, h.dev, stat.Ino, h.ino)
+	}
+	return h.fn, nil
+}
+
+func (h *handle) Close() error {
+	return nil
+}

vendor/src/github.com/tonistiigi/fifo/readme.md

@@ -0,0 +1,30 @@
+### fifo
+
+Go package for handling fifos in a sane way.
+
+```
+// OpenFifo opens a fifo. Returns io.ReadWriteCloser.
+// Context can be used to cancel this function until open(2) has not returned.
+// Accepted flags:
+// - syscall.O_CREAT - create new fifo if one doesn't exist
+// - syscall.O_RDONLY - open fifo only from reader side
+// - syscall.O_WRONLY - open fifo only from writer side
+// - syscall.O_RDWR - open fifo from both sides, never block on syscall level
+// - syscall.O_NONBLOCK - return io.ReadWriteCloser even if other side of the
+//     fifo isn't open. read/write will be connected after the actual fifo is
+//     open or after fifo is closed.
+func OpenFifo(ctx context.Context, fn string, flag int, perm os.FileMode) (io.ReadWriteCloser, error)
+
+
+// Read from a fifo to a byte array.
+func (f *fifo) Read(b []byte) (int, error)
+
+
+// Write from byte array to a fifo.
+func (f *fifo) Write(b []byte) (int, error)
+
+
+// Close the fifo. Next reads/writes will error. This method can also be used
+// before open(2) has returned and fifo was never opened.
+func (f *fifo) Close() error 
+```