Handle .drop_cache in Truncate and GetXAttr too.

Add test.

unionfs/unionfs.go

@@ -6,11 +6,11 @@ import (
 	"github.com/hanwen/go-fuse/fuse"
 	"log"
 	"os"
-	"syscall"
 	"path"
 	"path/filepath"
-	"sync"
 	"strings"
+	"sync"
+	"syscall"
 	"time"
 )
 
@@ -320,6 +320,10 @@ func (me *UnionFs) Symlink(pointedTo string, linkName string) (code fuse.Status)
 }
 
 func (me *UnionFs) Truncate(path string, offset uint64) (code fuse.Status) {
+	if path == _DROP_CACHE {
+		return fuse.OK
+	}
+
 	r := me.getBranch(path)
 	if r.branch > 0 {
 		code = me.Promote(path, r)
@@ -549,6 +553,10 @@ func (me *UnionFs) GetAttr(name string) (a *os.FileInfo, s fuse.Status) {
 }
 
 func (me *UnionFs) GetXAttr(name string, attr string) ([]byte, fuse.Status) {
+	if name == _DROP_CACHE {
+		return nil, syscall.ENODATA
+	}
+
 	r := me.getBranch(name)
 	if r.branch >= 0 {
 		return me.fileSystems[r.branch].GetXAttr(name, attr)

unionfs/unionfs_test.go

@@ -468,3 +468,44 @@ func TestRemoveAll(t *testing.T) {
 	}
 }
 
+func Readdirnames(dir string) ([]string, os.Error) {
+	f, err := os.Open(dir)
+	if err != nil {
+		return nil, err
+	}
+
+	defer f.Close()
+	return f.Readdirnames(-1)
+}
+
+func TestDropCache(t *testing.T) {
+	t.Log("TestDropCache")
+	wd, clean := setupUfs(t)
+	defer clean()
+
+	err := ioutil.WriteFile(wd + "/ro/file", []byte("bla"), 0644)
+	CheckSuccess(err)
+
+	_, err = os.Lstat(wd + "/mount/.drop_cache")
+	CheckSuccess(err)
+
+	names, err := Readdirnames(wd + "/mount")
+	CheckSuccess(err)
+	if len(names) != 1 || names[0] != "file"  {
+		t.Fatal("unexpected names", names)
+	}
+
+	err = ioutil.WriteFile(wd + "/ro/file2", []byte("blabla"), 0644)
+	names2, err := Readdirnames(wd + "/mount")
+	CheckSuccess(err)
+	if len(names2) != len(names) {
+		t.Fatal("mismatch", names2)
+	}
+
+	err = ioutil.WriteFile(wd + "/mount/.drop_cache", []byte("does not matter"), 0644)
+	CheckSuccess(err)
+	names2, err = Readdirnames(wd + "/mount")
+	if len(names2) != 2 {
+		t.Fatal("mismatch 2", names2)
+	}
+}