Merge pull request #2177 from crosbymichael/file-io

Refactor shim to support file logging

linux/proc/io.go

@@ -22,6 +22,7 @@ import (
 	"context"
 	"fmt"
 	"io"
+	"os"
 	"sync"
 	"syscall"
 
@@ -37,8 +38,14 @@ var bufPool = sync.Pool{
 }
 
 func copyPipes(ctx context.Context, rio runc.IO, stdin, stdout, stderr string, wg, cwg *sync.WaitGroup) error {
-	for name, dest := range map[string]func(wc io.WriteCloser, rc io.Closer){
+	var sameFile io.WriteCloser
-		stdout: func(wc io.WriteCloser, rc io.Closer) {
+	for _, i := range []struct {
+		name string
+		dest func(wc io.WriteCloser, rc io.Closer)
+	}{
+		{
+			name: stdout,
+			dest: func(wc io.WriteCloser, rc io.Closer) {
 				wg.Add(1)
 				cwg.Add(1)
 				go func() {
@@ -48,33 +55,58 @@ func copyPipes(ctx context.Context, rio runc.IO, stdin, stdout, stderr string, w
 					io.CopyBuffer(wc, rio.Stdout(), *p)
 					wg.Done()
 					wc.Close()
+					if rc != nil {
 						rc.Close()
+					}
 				}()
 			},
-		stderr: func(wc io.WriteCloser, rc io.Closer) {
+		}, {
+			name: stderr,
+			dest: func(wc io.WriteCloser, rc io.Closer) {
 				wg.Add(1)
 				cwg.Add(1)
 				go func() {
 					cwg.Done()
 					p := bufPool.Get().(*[]byte)
 					defer bufPool.Put(p)
-
 					io.CopyBuffer(wc, rio.Stderr(), *p)
 					wg.Done()
 					wc.Close()
+					if rc != nil {
 						rc.Close()
+					}
 				}()
 			},
+		},
 	} {
-		fw, err := fifo.OpenFifo(ctx, name, syscall.O_WRONLY, 0)
+		ok, err := isFifo(i.name)
 		if err != nil {
-			return fmt.Errorf("containerd-shim: opening %s failed: %s", name, err)
+			return err
 		}
-		fr, err := fifo.OpenFifo(ctx, name, syscall.O_RDONLY, 0)
+		var (
-		if err != nil {
+			fw io.WriteCloser
-			return fmt.Errorf("containerd-shim: opening %s failed: %s", name, err)
+			fr io.Closer
+		)
+		if ok {
+			if fw, err = fifo.OpenFifo(ctx, i.name, syscall.O_WRONLY, 0); err != nil {
+				return fmt.Errorf("containerd-shim: opening %s failed: %s", i.name, err)
 			}
-		dest(fw, fr)
+			if fr, err = fifo.OpenFifo(ctx, i.name, syscall.O_RDONLY, 0); err != nil {
+				return fmt.Errorf("containerd-shim: opening %s failed: %s", i.name, err)
+			}
+		} else {
+			if sameFile != nil {
+				i.dest(sameFile, nil)
+				continue
+			}
+			if fw, err = os.OpenFile(i.name, syscall.O_WRONLY|syscall.O_APPEND, 0); err != nil {
+				return fmt.Errorf("containerd-shim: opening %s failed: %s", i.name, err)
+			}
+			if stdout == stderr {
+				sameFile = fw
+			}
+		}
+		i.dest(fw, fr)
 	}
 	if stdin == "" {
 		rio.Stdin().Close()
@@ -96,3 +128,19 @@ func copyPipes(ctx context.Context, rio runc.IO, stdin, stdout, stderr string, w
 	}()
 	return nil
 }
+
+// isFifo checks if a file is a fifo
+// if the file does not exist then it returns false
+func isFifo(path string) (bool, error) {
+	stat, err := os.Stat(path)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return false, nil
+		}
+		return false, err
+	}
+	if stat.Mode()&os.ModeNamedPipe == os.ModeNamedPipe {
+		return true, nil
+	}
+	return false, nil
+}