container/opts: Add bind-create-src mount option

Add support for the `bind-create-src` option in bind mounts, which
instructs the daemon to create the source mountpoint on the host if it
doesn't exist.

This allows to replace the legacy `-v /src/dir:/dst` with the `--mount`.

Usage:
--mount type=bind,src=/host/path,dst=/container/path,bind-create-src
--mount type=bind,src=/host/path,dst=/container/path,bind-create-src=true

Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>

e2e/container/run_test.go

@@ -5,6 +5,7 @@ import (
 	"io"
 	"math/rand"
 	"os/exec"
+	"path/filepath"
 	"strings"
 	"syscall"
 	"testing"
@@ -160,6 +161,36 @@ func TestMountSubvolume(t *testing.T) {
 	}
 }
 
+func TestMountBindCreateMountpoint(t *testing.T) {
+	environment.SkipIfDaemonNotLinux(t)
+
+	for _, tc := range []struct {
+		name          string
+		value         string
+		expectSuccess bool
+	}{
+		{name: "flag only", value: "bind-create-src", expectSuccess: true},
+		{name: "true", value: "bind-create-src=true", expectSuccess: true},
+		{name: "1", value: "bind-create-src=1", expectSuccess: true},
+		{name: "false", value: "bind-create-src=false", expectSuccess: false},
+		{name: "0", value: "bind-create-src=0", expectSuccess: false},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			srcPath := filepath.Join("/tmp", t.Name(), "does", "not", "exist")
+			result := icmd.RunCommand("docker", "run", "--rm",
+				"--mount", "type=bind,src="+srcPath+",dst=/mnt,"+tc.value,
+				fixtures.AlpineImage, "cat", "/proc/mounts")
+			if tc.expectSuccess {
+				result.Assert(t, icmd.Success)
+				assert.Check(t, is.Contains(result.Stdout(), "/mnt"))
+			} else {
+				result.Assert(t, icmd.Expected{ExitCode: 125})
+				assert.Check(t, is.Contains(result.Stderr(), srcPath))
+			}
+		})
+	}
+}
+
 func TestProcessTermination(t *testing.T) {
 	var out bytes.Buffer
 	cmd := icmd.Command("docker", "run", "--rm", "-i", fixtures.AlpineImage,

opts/mount.go

@@ -57,7 +57,7 @@ func (m *MountOpt) Set(value string) error {
 
 		if !hasValue {
 			switch key {
-			case "readonly", "ro", "volume-nocopy", "bind-nonrecursive":
+			case "readonly", "ro", "volume-nocopy", "bind-nonrecursive", "bind-create-src":
 				// boolean values
 			default:
 				return fmt.Errorf("invalid field '%s' must be a key=value pair", field)
@@ -102,6 +102,11 @@ func (m *MountOpt) Set(value string) error {
 			default:
 				return fmt.Errorf(`invalid value for %s: %s (must be "enabled", "disabled", "writable", or "readonly")`, key, val)
 			}
+		case "bind-create-src":
+			ensureBindOptions(&mount).CreateMountpoint, err = parseBoolValue(key, val, hasValue)
+			if err != nil {
+				return err
+			}
 		case "volume-subpath":
 			ensureVolumeOptions(&mount).Subpath = val
 		case "volume-nocopy":

opts/mount_test.go

@@ -475,6 +475,50 @@ func TestMountOptSetTmpfsNoError(t *testing.T) {
 	}
 }
 
+func TestMountOptSetBindCreateSrc(t *testing.T) {
+	tests := []struct {
+		value  string
+		exp    bool
+		expErr string
+	}{
+		{value: "", exp: false},
+		{value: "bind-create-src", exp: true},
+		{value: "bind-create-src=", expErr: `invalid value for 'bind-create-src': value is empty`},
+		{value: "bind-create-src= true", expErr: `invalid value for 'bind-create-src' in 'bind-create-src= true': value should not have whitespace`},
+		{value: "bind-create-src=no", expErr: `invalid value for 'bind-create-src': invalid boolean value ("no"): must be one of "true", "1", "false", or "0" (default "true")`},
+		{value: "bind-create-src=1", exp: true},
+		{value: "bind-create-src=true", exp: true},
+		{value: "bind-create-src=0", exp: false},
+		{value: "bind-create-src=false", exp: false},
+	}
+
+	for _, tc := range tests {
+		name := tc.value
+		if name == "" {
+			name = "not set"
+		}
+		t.Run(name, func(t *testing.T) {
+			val := "type=bind,target=/foo,source=/foo"
+			if tc.value != "" {
+				val += "," + tc.value
+			}
+			var m MountOpt
+			err := m.Set(val)
+			if tc.expErr != "" {
+				assert.Error(t, err, tc.expErr)
+				return
+			}
+			assert.NilError(t, err)
+			if tc.value == "" {
+				assert.Check(t, is.Nil(m.values[0].BindOptions))
+			} else {
+				assert.Check(t, m.values[0].BindOptions != nil)
+				assert.Check(t, is.Equal(m.values[0].BindOptions.CreateMountpoint, tc.exp))
+			}
+		})
+	}
+}
+
 func TestMountOptSetBindRecursive(t *testing.T) {
 	t.Run("enabled", func(t *testing.T) {
 		var m MountOpt