Add open flags to OpenFileOp

conversions.go

@@ -255,8 +255,16 @@ func convertInMessage(
 		}
 
 	case fusekernel.OpOpen:
+		type input fusekernel.OpenIn
+		in := (*input)(inMsg.Consume(unsafe.Sizeof(input{})))
+
+		if in == nil {
+			err = errors.New("Corrupt OpOpen")
+			return
+		}
 		o = &fuseops.OpenFileOp{
 			Inode: fuseops.InodeID(inMsg.Header().Nodeid),
+			Flag:  int(in.Flags),
 		}
 
 	case fusekernel.OpOpendir:

fuseops/ops.go

@@ -593,6 +593,9 @@ type OpenFileOp struct {
 	// layer. This allows for filesystems whose file sizes are not known in
 	// advance, for example, because contents are generated on the fly.
 	UseDirectIO bool
+
+	// User-provided flags to open(2). See http://go/godoc/os/#OpenFile.
+	Flag int
 }
 
 // Read data from a file previously opened with CreateFile or OpenFile.

samples/memfs/memfs.go

@@ -26,6 +26,7 @@ import (
 	"github.com/jacobsa/fuse/fuseops"
 	"github.com/jacobsa/fuse/fuseutil"
 	"github.com/jacobsa/syncutil"
+	"golang.org/x/sys/unix"
 )
 
 type memFS struct {
@@ -615,6 +616,23 @@ func (fs *memFS) OpenFile(
 	if !inode.isFile() {
 		panic("Found non-file.")
 	}
+	// The flags are not a bitmask, they are a 2-bit field
+	// with, technically, only 3 legal values. But testing shows
+	// that there are 4 legal values, so we accomodate that.
+	var perm int
+	switch op.Flag & unix.O_ACCMODE {
+	case unix.O_RDONLY:
+		perm = 0400
+	case unix.O_WRONLY:
+		perm = 0200
+	case unix.O_RDWR, unix.O_ACCMODE:
+		perm = 0600
+	}
+
+	// We only check user permissions, since this is a sample FS
+	if int(inode.attrs.Mode.Perm())&perm != perm {
+		err = unix.EACCES
+	}
 
 	return
 }

samples/memfs/memfs_test.go

@@ -35,6 +35,7 @@ import (
 	. "github.com/jacobsa/oglematchers"
 	. "github.com/jacobsa/ogletest"
 	"github.com/kahing/go-xattr"
+	"golang.org/x/sys/unix"
 )
 
 func TestMemFS(t *testing.T) { RunTests(t) }
@@ -1706,6 +1707,30 @@ func (t *MemFSTest) RenameIntoFileSystem() {
 	ExpectThat(err, Error(HasSubstr("cross-device")))
 }
 
+func (t *MemFSTest) TestPermissions() {
+	var e = unix.EACCES
+	var test = []struct {
+		name string
+		mode int
+		res  [4]error
+	}{
+		{name: "ro", mode: 0400, res: [4]error{nil, e, e, e}},
+		{name: "wo", mode: 0200, res: [4]error{e, nil, e, e}},
+		{name: "rw", mode: 0600, res: [4]error{nil, nil, nil, nil}},
+	}
+
+	for _, tt := range test {
+		n := path.Join(t.Dir, tt.name)
+		err := ioutil.WriteFile(n, []byte(""), os.FileMode(tt.mode))
+		AssertEq(nil, err)
+		for f, r := range tt.res {
+			fd, err := unix.Open(n, f, 0)
+			unix.Close(fd)
+			AssertEq(r, err)
+		}
+	}
+}
+
 func (t *MemFSTest) RenameOverExistingFile() {
 	var err error