1 files changed, 80 insertions, 0 deletions
diff --git a/pkg/lisafs/communicator.go b/pkg/lisafs/communicator.go
new file mode 100644
index 000000000..ec2035158
--- /dev/null
+++ b/pkg/lisafs/communicator.go
@@ -0,0 +1,80 @@
+// Copyright 2021 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package lisafs
+
+import "golang.org/x/sys/unix"
+
+// Communicator is a server side utility which represents exactly how the
+// server is communicating with the client.
+type Communicator interface {
+	// PayloadBuf returns a slice to the payload section of its internal buffer
+	// where the message can be marshalled. The handlers should use this to
+	// populate the payload buffer with the message.
+	//
+	// The payload buffer contents *should* be preserved across calls with
+	// different sizes. Note that this is not a guarantee, because a compromised
+	// owner of a "shared" payload buffer can tamper with its contents anytime,
+	// even when it's not its turn to do so.
+	PayloadBuf(size uint32) []byte
+
+	// SndRcvMessage sends message m. The caller must have populated PayloadBuf()
+	// with payloadLen bytes. The caller expects to receive wantFDs FDs.
+	// Any received FDs must be accessible via ReleaseFDs(). It returns the
+	// response message along with the response payload length.
+	SndRcvMessage(m MID, payloadLen uint32, wantFDs uint8) (MID, uint32, error)
+
+	// DonateFD makes fd non-blocking and starts tracking it. The next call to
+	// ReleaseFDs will include fd in the order it was added. Communicator takes
+	// ownership of fd. Server side should call this.
+	DonateFD(fd int) error
+
+	// Track starts tracking fd. The next call to ReleaseFDs will include fd in
+	// the order it was added. Communicator takes ownership of fd. Client side
+	// should use this for accumulating received FDs.
+	TrackFD(fd int)
+
+	// ReleaseFDs returns the accumulated FDs and stops tracking them. The
+	// ownership of the FDs is transferred to the caller.
+	ReleaseFDs() []int
+}
+
+// fdTracker is a partial implementation of Communicator. It can be embedded in
+// Communicator implementations to keep track of FD donations.
+type fdTracker struct {
+	fds []int
+}
+
+// DonateFD implements Communicator.DonateFD.
+func (d *fdTracker) DonateFD(fd int) error {
+	// Make sure the FD is non-blocking.
+	if err := unix.SetNonblock(fd, true); err != nil {
+		unix.Close(fd)
+		return err
+	}
+	d.TrackFD(fd)
+	return nil
+}
+
+// TrackFD implements Communicator.TrackFD.
+func (d *fdTracker) TrackFD(fd int) {
+	d.fds = append(d.fds, fd)
+}
+
+// ReleaseFDs implements Communicator.ReleaseFDs.
+func (d *fdTracker) ReleaseFDs() []int {
+	ret := d.fds
+	d.fds = d.fds[:0]
+	return ret
+}