new: add host bind mounts

client/llb/exec.go

@@ -49,6 +49,7 @@ type mount struct {
 	cacheSharing CacheMountSharingMode
 	noOutput     bool
 	contentCache MountContentCache
+	hostPath     string
 }
 
 type ExecOp struct {
@@ -371,6 +372,10 @@ func (e *ExecOp) Marshal(ctx context.Context, c *Constraints) (digest.Digest, []
 			Output:   int64(outputIndex),
 			Selector: m.selector,
 		}
+		if m.hostPath != "" {
+			pm.MountType = pb.MountType_HOST_BIND
+			pm.HostPath = m.hostPath
+		}
 		if m.cacheID != "" {
 			pm.MountType = pb.MountType_CACHE
 			pm.CacheOpt = &pb.CacheOpt{
@@ -505,6 +510,19 @@ func (e ExecState) AddMount(target string, source State, opt ...MountOption) Sta
 	return source.WithOutput(e.exec.AddMount(target, source.Output(), opt...))
 }
 
+func AddHostBindMount(dest string, hostPath string, opts ...MountOption) RunOption {
+	return runOptionFunc(func(ei *ExecInfo) {
+		mountOpts := append(opts, func(m *mount) {
+			m.target = dest
+			m.hostPath = hostPath
+			m.noOutput = true
+			m.source = nil
+			m.output = nil
+		})
+		ei.Mounts = append(ei.Mounts, MountInfo{dest, nil, mountOpts})
+	})
+}
+
 func (e ExecState) GetMount(target string) State {
 	return NewState(e.exec.GetMount(target))
 }

frontend/gateway/container/container.go

@@ -236,6 +236,16 @@ func PrepareMounts(ctx context.Context, mm *mounts.MountManager, cm cache.Manage
 			if mountable == nil {
 				continue
 			}
+		case opspb.MountType_HOST_BIND:
+			mountable, err = mm.MountableHostBind(ctx, m, g)
+			if err != nil {
+				return p, err
+			}
+			if mountable == nil {
+				continue // or handle error if necessary
+			}
+        // Since this is a direct host mount, we may not need to handle outputs or cache.
+        // Proceed to add this mountable to the list of mounts.
 
 		default:
 			return p, errors.Errorf("mount type %s not implemented", m.MountType)

solver/llbsolver/mounts/mount.go

@@ -582,3 +582,55 @@ func (md CacheRefMetadata) setCacheDirIndex(id string) error {
 func (md CacheRefMetadata) ClearCacheDirIndex() error {
 	return md.ClearValueAndIndex(keyCacheDir, cacheDirIndex)
 }
+
+func (mm *MountManager) MountableHostBind(ctx context.Context, m *pb.Mount, g session.Group) (cache.Mountable, error) {
+	return mm.getHostBindMountable(ctx, m, g)
+}
+
+func (mm *MountManager) getHostBindMountable(ctx context.Context, m *pb.Mount, g session.Group) (cache.Mountable, error) {
+	if m.HostPath == "" {
+		return nil, errors.Errorf("hostPath must be specified for HOST_BIND mount")
+	}
+	return &hostBindMount{
+		hostPath: m.HostPath,
+		readonly: m.Readonly,
+	}, nil
+}
+
+type hostBindMount struct {
+	hostPath string
+	readonly bool
+}
+
+func (hbm *hostBindMount) Mount(ctx context.Context, readonly bool, g session.Group) (snapshot.Mountable, error) {
+	return &hostBindMountInstance{
+		hostPath: hbm.hostPath,
+		readonly: hbm.readonly || readonly,
+	}, nil
+}
+
+type hostBindMountInstance struct {
+	hostPath string
+	readonly bool
+}
+
+func (hbm *hostBindMountInstance) Mount() ([]mount.Mount, func() error, error) {
+	options := []string{"rbind"}
+	if hbm.readonly {
+		options = append(options, "ro")
+	}
+
+	return []mount.Mount{
+		{
+			Type:	"bind",
+			Source:  hbm.hostPath,
+			Options: options,
+		},
+	}, func() error { return nil }, nil
+
+}
+
+// Implement IdentityMapping method
+func (hbm *hostBindMountInstance) IdentityMapping() *idtools.IdentityMapping {
+	return nil
+}

solver/llbsolver/ops/exec.go

@@ -117,6 +117,11 @@ func (e *ExecOp) CacheMap(ctx context.Context, g session.Group, index int) (*sol
 		m := op.Mounts[i]
 		m.Selector = ""
 
+		// clear hostpath from MountType_HOST_BIND
+		if m.MountType == pb.MountType_HOST_BIND {
+			m.HostPath = ""
+		}
+
 		if checkShouldClearCacheOpts(m) {
 			m.CacheOpt.ID = ""
 			m.CacheOpt.Sharing = 0
@@ -268,7 +273,7 @@ func (e *ExecOp) getMountDeps() ([]dep, error) {
 	deps := make([]dep, e.numInputs)
 	for _, m := range e.op.Mounts {
 		switch m.MountType {
-		case pb.MountType_SECRET, pb.MountType_SSH, pb.MountType_TMPFS:
+		case pb.MountType_SECRET, pb.MountType_SSH, pb.MountType_TMPFS, pb.MountType_HOST_BIND:
 			continue
 		}