pkg/mount: refactor Unmount()

It has been pointed out that we're ignoring EINVAL from umount(2)
everywhere, so let's move it to a lower-level function. Also, its
implementation should be the same for any UNIX incarnation, so
let's consolidate it.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

pkg/mount/mount.go

@@ -3,7 +3,6 @@ package mount // import "github.com/docker/docker/pkg/mount"
 import (
 	"sort"
 	"strings"
-	"syscall"
 
 	"github.com/sirupsen/logrus"
 )
@@ -89,12 +88,7 @@ func ForceMount(device, target, mType, options string) error {
 // Unmount lazily unmounts a filesystem on supported platforms, otherwise
 // does a normal unmount.
 func Unmount(target string) error {
-	err := unmount(target, mntDetach)
-	if err == syscall.EINVAL {
-		// ignore "not mounted" error
-		err = nil
-	}
-	return err
+	return unmount(target, mntDetach)
 }
 
 // RecursiveUnmount unmounts the target and all mounts underneath, starting with
@@ -114,25 +108,14 @@ func RecursiveUnmount(target string) error {
 		logrus.Debugf("Trying to unmount %s", m.Mountpoint)
 		err = unmount(m.Mountpoint, mntDetach)
 		if err != nil {
-			// If the error is EINVAL either this whole package is wrong (invalid flags passed to unmount(2)) or this is
-			// not a mountpoint (which is ok in this case).
-			// Meanwhile calling `Mounted()` is very expensive.
-			//
-			// We've purposefully used `syscall.EINVAL` here instead of `unix.EINVAL` to avoid platform branching
-			// Since `EINVAL` is defined for both Windows and Linux in the `syscall` package (and other platforms),
-			//   this is nicer than defining a custom value that we can refer to in each platform file.
-			if err == syscall.EINVAL {
-				continue
-			}
-			if i == len(mounts)-1 {
+			if i == len(mounts)-1 { // last mount
 				if mounted, e := Mounted(m.Mountpoint); e != nil || mounted {
 					return err
 				}
-				continue
+			} else {
+				// This is some submount, we can ignore this error for now, the final unmount will fail if this is a real problem
+				logrus.WithError(err).Warnf("Failed to unmount submount %s", m.Mountpoint)
 			}
-			// This is some submount, we can ignore this error for now, the final unmount will fail if this is a real problem
-			logrus.WithError(err).Warnf("Failed to unmount submount %s", m.Mountpoint)
-			continue
 		}
 
 		logrus.Debugf("Unmounted %s", m.Mountpoint)

pkg/mount/mounter_freebsd.go

@@ -14,8 +14,6 @@ import (
 	"fmt"
 	"strings"
 	"unsafe"
-
-	"golang.org/x/sys/unix"
 )
 
 func allocateIOVecs(options []string) []C.struct_iovec {
@@ -54,7 +52,3 @@ func mount(device, target, mType string, flag uintptr, data string) error {
 	}
 	return nil
 }
-
-func unmount(target string, flag int) error {
-	return unix.Unmount(target, flag)
-}

pkg/mount/mounter_linux.go

@@ -51,7 +51,3 @@ func mount(device, target, mType string, flags uintptr, data string) error {
 
 	return nil
 }
-
-func unmount(target string, flag int) error {
-	return unix.Unmount(target, flag)
-}

pkg/mount/unmount_unix.go

@@ -0,0 +1,17 @@
+// +build !windows
+
+package mount // import "github.com/docker/docker/pkg/mount"
+
+import "golang.org/x/sys/unix"
+
+func unmount(target string, flags int) error {
+	err := unix.Unmount(target, flags)
+	if err == unix.EINVAL {
+		// Ignore "not mounted" error here. Note the same error
+		// can be returned if flags are invalid, so this code
+		// assumes that the flags value is always correct.
+		err = nil
+	}
+
+	return err
+}