mount: Add `volume-subpath` option

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

e2e/container/run_test.go

@@ -2,10 +2,12 @@ package container
 
 import (
 	"fmt"
+	"strings"
 	"testing"
 
 	"github.com/docker/cli/e2e/internal/fixtures"
 	"github.com/docker/cli/internal/test/environment"
+	"github.com/docker/docker/api/types/versions"
 	"gotest.tools/v3/assert"
 	is "gotest.tools/v3/assert/cmp"
 	"gotest.tools/v3/golden"
@@ -149,3 +151,56 @@ func TestRunWithCgroupNamespace(t *testing.T) {
 		"cat", "/sys/fs/cgroup/cgroup.controllers")
 	result.Assert(t, icmd.Success)
 }
+
+func TestMountSubvolume(t *testing.T) {
+	skip.If(t, versions.LessThan(environment.DaemonAPIVersion(t), "1.45"))
+
+	volName := "test-volume-" + t.Name()
+	icmd.RunCommand("docker", "volume", "create", volName).Assert(t, icmd.Success)
+
+	t.Cleanup(func() {
+		icmd.RunCommand("docker", "volume", "remove", "-f", volName).Assert(t, icmd.Success)
+	})
+
+	defaultMountOpts := []string{
+		"type=volume",
+		"src=" + volName,
+		"dst=/volume",
+	}
+
+	// Populate the volume with test data.
+	icmd.RunCommand("docker", "run", "--rm", "--mount", strings.Join(defaultMountOpts, ","), fixtures.AlpineImage, "sh", "-c",
+		"echo foo > /volume/bar.txt && "+
+			"mkdir /volume/etc && echo root > /volume/etc/passwd && "+
+			"mkdir /volume/subdir && echo world > /volume/subdir/hello.txt;",
+	).Assert(t, icmd.Success)
+
+	runMount := func(cmd string, mountOpts ...string) *icmd.Result {
+		mountArg := strings.Join(append(defaultMountOpts, mountOpts...), ",")
+		return icmd.RunCommand("docker", "run", "--rm", "--mount", mountArg, fixtures.AlpineImage, cmd, "/volume")
+	}
+
+	for _, tc := range []struct {
+		name    string
+		cmd     string
+		subpath string
+
+		expectedOut  string
+		expectedErr  string
+		expectedCode int
+	}{
+		{name: "absolute", cmd: "cat", subpath: "/etc/passwd", expectedErr: "subpath must be a relative path within the volume", expectedCode: 125},
+		{name: "subpath not exists", cmd: "ls", subpath: "some-path/that/doesnt-exist", expectedErr: "cannot access path ", expectedCode: 127},
+		{name: "subdirectory mount", cmd: "ls", subpath: "subdir", expectedOut: "hello.txt"},
+		{name: "file mount", cmd: "cat", subpath: "bar.txt", expectedOut: "foo"},
+	} {
+		tc := tc
+		t.Run(tc.name, func(t *testing.T) {
+			runMount(tc.cmd, "volume-subpath="+tc.subpath).Assert(t, icmd.Expected{
+				Err:      tc.expectedErr,
+				ExitCode: tc.expectedCode,
+				Out:      tc.expectedOut,
+			})
+		})
+	}
+}

opts/mount.go

@@ -131,6 +131,8 @@ func (m *MountOpt) Set(value string) error {
 				return fmt.Errorf("invalid value for %s: %s (must be \"enabled\", \"disabled\", \"writable\", or \"readonly\")",
 					key, val)
 			}
+		case "volume-subpath":
+			volumeOptions().Subpath = val
 		case "volume-nocopy":
 			volumeOptions().NoCopy, err = strconv.ParseBool(val)
 			if err != nil {