fs: implement Write for MemRegularFile

Change-Id: Iac5c1a8329ceb0d8538029bd737cfede2af4d9a2

fs/mem.go

@@ -6,6 +6,7 @@ package fs
 
 import (
 	"context"
+	"sync"
 	"syscall"
 
 	"github.com/hanwen/go-fuse/v2/fuse"
@@ -15,35 +16,65 @@ import (
 // slice in memory.
 type MemRegularFile struct {
 	Inode
+
+	mu   sync.Mutex
 	Data []byte
 	Attr fuse.Attr
 }
 
 var _ = (NodeOpener)((*MemRegularFile)(nil))
 var _ = (NodeReader)((*MemRegularFile)(nil))
+var _ = (NodeWriter)((*MemRegularFile)(nil))
+var _ = (NodeSetattrer)((*MemRegularFile)(nil))
 var _ = (NodeFlusher)((*MemRegularFile)(nil))
 
 func (f *MemRegularFile) Open(ctx context.Context, flags uint32) (fh FileHandle, fuseFlags uint32, errno syscall.Errno) {
-	if flags&(syscall.O_RDWR) != 0 || flags&syscall.O_WRONLY != 0 {
-		return nil, 0, syscall.EPERM
+	return nil, fuse.FOPEN_KEEP_CACHE, OK
+}
+
+func (f *MemRegularFile) Write(ctx context.Context, fh FileHandle, data []byte, off int64) (uint32, syscall.Errno) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	end := int64(len(data)) + off
+	if int64(len(f.Data)) < end {
+		n := make([]byte, end)
+		copy(n, f.Data)
+		f.Data = n
 	}
 
-	return nil, fuse.FOPEN_KEEP_CACHE, OK
+	copy(f.Data[off:off+int64(len(data))], data)
+
+	return uint32(len(data)), 0
 }
 
 var _ = (NodeGetattrer)((*MemRegularFile)(nil))
 
 func (f *MemRegularFile) Getattr(ctx context.Context, fh FileHandle, out *fuse.AttrOut) syscall.Errno {
+	f.mu.Lock()
+	defer f.mu.Unlock()
 	out.Attr = f.Attr
 	out.Attr.Size = uint64(len(f.Data))
 	return OK
 }
 
+func (f *MemRegularFile) Setattr(ctx context.Context, fh FileHandle, in *fuse.SetAttrIn, out *fuse.AttrOut) syscall.Errno {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	if sz, ok := in.GetSize(); ok {
+		f.Data = f.Data[:sz]
+	}
+	out.Attr = f.Attr
+	out.Size = uint64(len(f.Data))
+	return OK
+}
+
 func (f *MemRegularFile) Flush(ctx context.Context, fh FileHandle) syscall.Errno {
 	return 0
 }
 
 func (f *MemRegularFile) Read(ctx context.Context, fh FileHandle, dest []byte, off int64) (fuse.ReadResult, syscall.Errno) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
 	end := int(off) + len(dest)
 	if end > len(f.Data) {
 		end = len(f.Data)

fs/mem_test.go

@@ -64,7 +64,6 @@ func TestDefaultOwner(t *testing.T) {
 	} else if st.Uid != 42 || st.Gid != 43 {
 		t.Fatalf("Got Lstat %d, %d want 42,43", st.Uid, st.Gid)
 	}
-
 }
 
 func TestDataFile(t *testing.T) {
@@ -116,6 +115,17 @@ func TestDataFile(t *testing.T) {
 	if got != want {
 		t.Errorf("got %q want %q", got, want)
 	}
+
+	replace := []byte("replaced!")
+	if err := ioutil.WriteFile(mntDir+"/file", replace, 0644); err != nil {
+		t.Fatalf("WriteFile: %v", err)
+	}
+
+	if gotBytes, err := ioutil.ReadFile(mntDir + "/file"); err != nil {
+		t.Fatalf("ReadFile: %v", err)
+	} else if bytes.Compare(replace, gotBytes) != 0 {
+		t.Fatalf("read: got %q want %q", gotBytes, replace)
+	}
 }
 
 func TestDataFileLargeRead(t *testing.T) {