Update mtime field in the cache for Open() and Truncate() calls.

This should fix Emacs save problems more robustly.

unionfs/unionfs.go

@@ -13,6 +13,7 @@ import (
 	"path/filepath"
 	"sync"
 	"strings"
+	"time"
 )
 
 // TODO(hanwen): is md5 sufficiently fast?
@@ -346,6 +347,7 @@ func (me *UnionFs) Truncate(path string, offset uint64) (code fuse.Status) {
 	}
 	if code.Ok() { 
 		r.attr.Size = int64(offset)
+		r.attr.Mtime_ns = time.Nanoseconds()
 		me.branchCache.Set(path, r)
 	}
 	return code
@@ -688,22 +690,22 @@ func (me *UnionFs) Rename(src string, dst string) (code fuse.Status) {
 
 func (me *UnionFs) Open(name string, flags uint32) (fuseFile fuse.File, status fuse.Status) {
 	r := me.getBranch(name)
-	branch := r.branch
 	if flags&fuse.O_ANYWRITE != 0 && r.branch > 0 {
 		code := me.Promote(name, r)
 		if code != fuse.OK {
 			return nil, code
 		}
-		branch = 0
+		r.branch = 0
+		r.attr.Mtime_ns = time.Nanoseconds()
+		me.branchCache.Set(name, r)
 	}
-	return me.fileSystems[branch].Open(name, uint32(flags))
+	return me.fileSystems[r.branch].Open(name, uint32(flags))
 }
 
 func (me *UnionFs) Release(name string) {
-	r := me.getBranch(name)
-	fresh := me.getBranchAttrNoCache(name)
-	r.attr.Size = fresh.attr.Size
-	me.branchCache.Set(name, r)
+	// Refresh timestamps and size field.
+	me.branchCache.DropEntry(name)
+	me.getBranch(name)
 }
 
 func (me *UnionFs) Roots() (result []string) {

unionfs/unionfs_test.go

@@ -416,3 +416,33 @@ func TestCopyChmod(t *testing.T) {
 		t.Errorf("uncached attr error %o", fi.Mode)
 	}
 }
+
+func abs(dt int64) int64 {
+	if dt >= 0 {
+		return dt
+	} 
+	return -dt
+}
+
+func TestTruncateTimestamp(t *testing.T) {
+	t.Log("TestTruncateTimestamp")
+	wd, state := setupUfs(t)
+	defer state.Unmount()
+
+	contents := "hello"
+	fn := wd + "/mount/y"
+	err := ioutil.WriteFile(fn, []byte(contents), 0644)
+	CheckSuccess(err)
+	time.Sleep(0.2e9)
+
+	truncTs := time.Nanoseconds()
+	err = os.Truncate(fn, 3)
+	CheckSuccess(err)
+
+	fi, err := os.Lstat(fn)
+	CheckSuccess(err)
+
+	if abs(truncTs - fi.Mtime_ns) > 0.1e9 {
+		t.Error("timestamp drift", truncTs, fi.Mtime_ns)
+	}
+}