3 files changed, 46 insertions, 13 deletions
diff --git a/pkg/flipcall/BUILD b/pkg/flipcall/BUILD
index 9c5ad500b..aa8e4e1f3 100644
--- a/pkg/flipcall/BUILD
+++ b/pkg/flipcall/BUILD
@@ -11,6 +11,7 @@ go_library(
         "futex_linux.go",
         "io.go",
         "packet_window_allocator.go",
+        "packet_window_mmap.go",
     ],
     visibility = ["//visibility:public"],
     deps = [
diff --git a/pkg/flipcall/flipcall.go b/pkg/flipcall/flipcall.go
index 3cdb576e1..c4a3366ce 100644
--- a/pkg/flipcall/flipcall.go
+++ b/pkg/flipcall/flipcall.go
@@ -95,7 +95,7 @@ func (ep *Endpoint) Init(side EndpointSide, pwd PacketWindowDescriptor, opts ...
 	if pwd.Length > math.MaxUint32 {
 		return fmt.Errorf("packet window size (%d) exceeds maximum (%d)", pwd.Length, math.MaxUint32)
 	}
-	m, _, e := syscall.RawSyscall6(syscall.SYS_MMAP, 0, uintptr(pwd.Length), syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_SHARED, uintptr(pwd.FD), uintptr(pwd.Offset))
+	m, e := packetWindowMmap(pwd)
 	if e != 0 {
 		return fmt.Errorf("failed to mmap packet window: %v", e)
 	}
@@ -179,8 +179,10 @@ const (
 
 // Connect blocks until the peer Endpoint has called Endpoint.RecvFirst().
 //
-// Preconditions: ep is a client Endpoint. ep.Connect(), ep.RecvFirst(),
-// ep.SendRecv(), and ep.SendLast() have never been called.
+// Preconditions:
+// * ep is a client Endpoint.
+// * ep.Connect(), ep.RecvFirst(), ep.SendRecv(), and ep.SendLast() have never
+//   been called.
 func (ep *Endpoint) Connect() error {
 	err := ep.ctrlConnect()
 	if err == nil {
@@ -192,8 +194,9 @@ func (ep *Endpoint) Connect() error {
 // RecvFirst blocks until the peer Endpoint calls Endpoint.SendRecv(), then
 // returns the datagram length specified by that call.
 //
-// Preconditions: ep is a server Endpoint. ep.SendRecv(), ep.RecvFirst(), and
-// ep.SendLast() have never been called.
+// Preconditions:
+// * ep is a server Endpoint.
+// * ep.SendRecv(), ep.RecvFirst(), and ep.SendLast() have never been called.
 func (ep *Endpoint) RecvFirst() (uint32, error) {
 	if err := ep.ctrlWaitFirst(); err != nil {
 		return 0, err
@@ -211,10 +214,12 @@ func (ep *Endpoint) RecvFirst() (uint32, error) {
 // datagram length, then blocks until the peer Endpoint calls
 // Endpoint.SendRecv() or Endpoint.SendLast().
 //
-// Preconditions: dataLen <= ep.DataCap(). No previous call to ep.SendRecv() or
-// ep.RecvFirst() has returned an error. ep.SendLast() has never been called.
-// If ep is a client Endpoint, ep.Connect() has previously been called and
-// returned nil.
+// Preconditions:
+// * dataLen <= ep.DataCap().
+// * No previous call to ep.SendRecv() or ep.RecvFirst() has returned an error.
+// * ep.SendLast() has never been called.
+// * If ep is a client Endpoint, ep.Connect() has previously been called and
+//   returned nil.
 func (ep *Endpoint) SendRecv(dataLen uint32) (uint32, error) {
 	if dataLen > ep.dataCap {
 		panic(fmt.Sprintf("attempting to send packet with datagram length %d (maximum %d)", dataLen, ep.dataCap))
@@ -240,10 +245,12 @@ func (ep *Endpoint) SendRecv(dataLen uint32) (uint32, error) {
 // SendLast causes the peer Endpoint's call to Endpoint.SendRecv() or
 // Endpoint.RecvFirst() to return with the given datagram length.
 //
-// Preconditions: dataLen <= ep.DataCap(). No previous call to ep.SendRecv() or
-// ep.RecvFirst() has returned an error. ep.SendLast() has never been called.
-// If ep is a client Endpoint, ep.Connect() has previously been called and
-// returned nil.
+// Preconditions:
+// * dataLen <= ep.DataCap().
+// * No previous call to ep.SendRecv() or ep.RecvFirst() has returned an error.
+// * ep.SendLast() has never been called.
+// * If ep is a client Endpoint, ep.Connect() has previously been called and
+//   returned nil.
 func (ep *Endpoint) SendLast(dataLen uint32) error {
 	if dataLen > ep.dataCap {
 		panic(fmt.Sprintf("attempting to send packet with datagram length %d (maximum %d)", dataLen, ep.dataCap))
diff --git a/pkg/flipcall/packet_window_mmap.go b/pkg/flipcall/packet_window_mmap.go
new file mode 100644
index 000000000..869183b11
--- /dev/null
+++ b/pkg/flipcall/packet_window_mmap.go
@@ -0,0 +1,25 @@
+// Copyright 2020 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 flipcall
+
+import (
+	"syscall"
+)
+
+// Return a memory mapping of the pwd in memory that can be shared outside the sandbox.
+func packetWindowMmap(pwd PacketWindowDescriptor) (uintptr, syscall.Errno) {
+	m, _, err := syscall.RawSyscall6(syscall.SYS_MMAP, 0, uintptr(pwd.Length), syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_SHARED, uintptr(pwd.FD), uintptr(pwd.Offset))
+	return m, err
+}