dockerfile: enable tmpfs mounts on run —mount

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

frontend/dockerfile/dockerfile2llb/convert_runmount.go

@@ -16,11 +16,11 @@ func detectRunMount(cmd *command, dispatchStatesByName map[string]*dispatchState
 		mounts := instructions.GetMounts(c)
 		sources := make([]*dispatchState, len(mounts))
 		for i, mount := range mounts {
-			if mount.From == "" && mount.Type == "cache" {
+			if mount.From == "" && mount.Type == instructions.MountTypeCache {
 				mount.From = emptyImageName
 			}
 			from := mount.From
-			if from == "" {
+			if from == "" || mount.Type == instructions.MountTypeTmpfs {
 				continue
 			}
 			stn, ok := dispatchStatesByName[strings.ToLower(from)]
@@ -45,7 +45,7 @@ func dispatchRunMounts(d *dispatchState, c *instructions.RunCommand, sources []*
 	mounts := instructions.GetMounts(c)
 
 	for i, mount := range mounts {
-		if mount.From == "" && mount.Type == "cache" {
+		if mount.From == "" && mount.Type == instructions.MountTypeCache {
 			mount.From = emptyImageName
 		}
 		st := opt.buildContext
@@ -53,10 +53,14 @@ func dispatchRunMounts(d *dispatchState, c *instructions.RunCommand, sources []*
 			st = sources[i].state
 		}
 		var mountOpts []llb.MountOption
+		if mount.Type == instructions.MountTypeTmpfs {
+			st = llb.Scratch()
+			mountOpts = append(mountOpts, llb.Tmpfs())
+		}
 		if mount.ReadOnly {
 			mountOpts = append(mountOpts, llb.Readonly)
 		}
-		if mount.Type == "cache" {
+		if mount.Type == instructions.MountTypeCache {
 			mountOpts = append(mountOpts, llb.AsPersistentCacheDir(opt.cacheIDNamespace+"/"+mount.CacheID))
 		}
 		if src := path.Join("/", mount.Source); src != "/" {

frontend/dockerfile/instructions/commands_runmount.go

@@ -10,6 +10,16 @@ import (
 	"github.com/pkg/errors"
 )
 
+const MountTypeBind = "bind"
+const MountTypeCache = "cache"
+const MountTypeTmpfs = "tmpfs"
+
+var allowedMountTypes = map[string]struct{}{
+	MountTypeBind:  {},
+	MountTypeCache: {},
+	MountTypeTmpfs: {},
+}
+
 type mountsKeyT string
 
 var mountsKey = mountsKeyT("dockerfile/run/mounts")
@@ -19,6 +29,11 @@ func init() {
 	parseRunPostHooks = append(parseRunPostHooks, runMountPostHook)
 }
 
+func isValidMountType(s string) bool {
+	_, ok := allowedMountTypes[s]
+	return ok
+}
+
 func runMountPreHook(cmd *RunCommand, req parseRequest) error {
 	st := &mountState{}
 	st.flag = req.flags.AddStrings("mount")
@@ -76,7 +91,7 @@ func parseMount(value string) (*Mount, error) {
 		return nil, errors.Wrap(err, "failed to parse csv mounts")
 	}
 
-	m := &Mount{Type: "bind"}
+	m := &Mount{Type: MountTypeBind}
 
 	roAuto := true
 
@@ -104,11 +119,7 @@ func parseMount(value string) (*Mount, error) {
 		value := parts[1]
 		switch key {
 		case "type":
-			allowedTypes := map[string]struct{}{
-				"cache": {},
-				"bind":  {},
-			}
-			if _, ok := allowedTypes[strings.ToLower(value)]; !ok {
+			if !isValidMountType(strings.ToLower(value)) {
 				return nil, errors.Errorf("invalid mount type %q", value)
 			}
 			m.Type = strings.ToLower(value)
@@ -139,7 +150,7 @@ func parseMount(value string) (*Mount, error) {
 	}
 
 	if roAuto {
-		if m.Type == "cache" {
+		if m.Type == MountTypeCache {
 			m.ReadOnly = false
 		} else {
 			m.ReadOnly = true

solver/llbsolver/ops/exec.go

@@ -401,7 +401,7 @@ func (m *tmpfsMount) Mount() ([]mount.Mount, error) {
 	}
 	return []mount.Mount{{
 		Type:    "tmpfs",
-		Source:  "none",
+		Source:  "tmpfs",
 		Options: opt,
 	}}, nil
 }