dockerfile: allow content cache for rw mounts

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

client/llb/exec.go

@@ -53,7 +53,7 @@ type mount struct {
 	cacheID      string
 	tmpfs        bool
 	cacheSharing CacheMountSharingMode
-	// hasOutput bool
+	noOutput     bool
 }
 
 type ExecOp struct {
@@ -80,6 +80,8 @@ func (e *ExecOp) AddMount(target string, source Output, opt ...MountOption) Outp
 		m.output = source
 	} else if m.tmpfs {
 		m.output = &output{vertex: e, err: errors.Errorf("tmpfs mount for %s can't be used as a parent", target)}
+	} else if m.noOutput {
+		m.output = &output{vertex: e, err: errors.Errorf("mount marked no-output and %s can't be used as a parent", target)}
 	} else {
 		o := &output{vertex: e, getIndex: e.getMountIndexFn(m)}
 		if p := e.constraints.Platform; p != nil {
@@ -248,7 +250,7 @@ func (e *ExecOp) Marshal(c *Constraints) (digest.Digest, []byte, *pb.OpMetadata,
 		}
 
 		outputIndex := pb.OutputIndex(-1)
-		if !m.readonly && m.cacheID == "" && !m.tmpfs {
+		if !m.noOutput && !m.readonly && m.cacheID == "" && !m.tmpfs {
 			outputIndex = pb.OutputIndex(outIndex)
 			outIndex++
 		}
@@ -344,7 +346,7 @@ func (e *ExecOp) getMountIndexFn(m *mount) func() (pb.OutputIndex, error) {
 
 		i := 0
 		for _, m2 := range e.mounts {
-			if m2.readonly || m2.cacheID != "" {
+			if m2.noOutput || m2.readonly || m2.cacheID != "" {
 				continue
 			}
 			if m == m2 {
@@ -385,6 +387,10 @@ func SourcePath(src string) MountOption {
 	}
 }
 
+func ForceNoOutput(m *mount) {
+	m.noOutput = true
+}
+
 func AsPersistentCacheDir(id string, sharing CacheMountSharingMode) MountOption {
 	return func(m *mount) {
 		m.cacheID = id

frontend/dockerfile/dockerfile2llb/convert_runmount.go

@@ -75,6 +75,8 @@ func dispatchRunMounts(d *dispatchState, c *instructions.RunCommand, sources []*
 		}
 		if mount.ReadOnly {
 			mountOpts = append(mountOpts, llb.Readonly)
+		} else if mount.Type == instructions.MountTypeBind {
+			mountOpts = append(mountOpts, llb.ForceNoOutput)
 		}
 		if mount.Type == instructions.MountTypeCache {
 			sharing := llb.CacheMountShared

frontend/dockerfile/dockerfile_mount_test.go

@@ -4,7 +4,9 @@ package dockerfile
 
 import (
 	"context"
+	"io/ioutil"
 	"os"
+	"path/filepath"
 	"testing"
 
 	"github.com/containerd/continuity/fs/fstest"
@@ -17,6 +19,7 @@ import (
 var mountTests = []integration.Test{
 	testMountContext,
 	testMountTmpfs,
+	testMountRWCache,
 }
 
 func init() {
@@ -78,3 +81,81 @@ RUN [ ! -f /mytmp/foo ]
 	}, nil)
 	require.NoError(t, err)
 }
+
+func testMountRWCache(t *testing.T, sb integration.Sandbox) {
+	f := getFrontend(t, sb)
+
+	dockerfile := []byte(`
+from busybox AS build
+copy cachebust /
+run mkdir out && echo foo > out/foo
+
+from busybox as second
+RUN --mount=from=build,src=out,target=/out,rw cat /dev/urandom | head -c 100 | sha256sum > /unique
+
+from scratch
+COPY --from=second /unique /unique
+`)
+
+	dir, err := tmpdir(
+		fstest.CreateFile("Dockerfile", dockerfile, 0600),
+		fstest.CreateFile("cachebust", []byte("0"), 0600),
+	)
+	require.NoError(t, err)
+	defer os.RemoveAll(dir)
+
+	c, err := client.New(context.TODO(), sb.Address())
+	require.NoError(t, err)
+	defer c.Close()
+
+	destDir, err := ioutil.TempDir("", "buildkit")
+	require.NoError(t, err)
+	defer os.RemoveAll(destDir)
+
+	_, err = f.Solve(context.TODO(), c, client.SolveOpt{
+		Exports: []client.ExportEntry{
+			{
+				Type:      client.ExporterLocal,
+				OutputDir: destDir,
+			},
+		},
+		LocalDirs: map[string]string{
+			builder.DefaultLocalNameDockerfile: dir,
+			builder.DefaultLocalNameContext:    dir,
+		},
+	}, nil)
+	require.NoError(t, err)
+
+	dt1, err := ioutil.ReadFile(filepath.Join(destDir, "unique"))
+	require.NoError(t, err)
+
+	// repeat with changed file that should be still cached by content
+	dir, err = tmpdir(
+		fstest.CreateFile("Dockerfile", dockerfile, 0600),
+		fstest.CreateFile("cachebust", []byte("1"), 0600),
+	)
+	require.NoError(t, err)
+	defer os.RemoveAll(dir)
+
+	destDir, err = ioutil.TempDir("", "buildkit")
+	require.NoError(t, err)
+	defer os.RemoveAll(destDir)
+
+	_, err = f.Solve(context.TODO(), c, client.SolveOpt{
+		Exports: []client.ExportEntry{
+			{
+				Type:      client.ExporterLocal,
+				OutputDir: destDir,
+			},
+		},
+		LocalDirs: map[string]string{
+			builder.DefaultLocalNameDockerfile: dir,
+			builder.DefaultLocalNameContext:    dir,
+		},
+	}, nil)
+	require.NoError(t, err)
+
+	dt2, err := ioutil.ReadFile(filepath.Join(destDir, "unique"))
+	require.NoError(t, err)
+	require.Equal(t, dt1, dt2)
+}

solver/llbsolver/ops/exec.go

@@ -209,7 +209,7 @@ func (e *execOp) getMountDeps() ([]dep, error) {
 			deps[m.Input].Selectors = append(deps[m.Input].Selectors, sel)
 		}
 
-		if !m.Readonly || m.Dest == pb.RootMount { // exclude read-only rootfs
+		if (!m.Readonly || m.Dest == pb.RootMount) && m.Output != -1 { // exclude read-only rootfs && read-write mounts
 			deps[m.Input].NoContentBasedHash = true
 		}
 	}