2 files changed, 150 insertions, 0 deletions
diff --git a/pkg/fdchannel/fdchannel_state_autogen.go b/pkg/fdchannel/fdchannel_state_autogen.go
new file mode 100755
index 000000000..8dbf80cba
--- /dev/null
+++ b/pkg/fdchannel/fdchannel_state_autogen.go
@@ -0,0 +1,4 @@
+// automatically generated by stateify.
+
+package fdchannel
+
diff --git a/pkg/fdchannel/fdchannel_unsafe.go b/pkg/fdchannel/fdchannel_unsafe.go
new file mode 100755
index 000000000..367235be5
--- /dev/null
+++ b/pkg/fdchannel/fdchannel_unsafe.go
@@ -0,0 +1,146 @@
+// Copyright 2019 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.
+
+// +build aix darwin dragonfly freebsd linux netbsd openbsd solaris
+
+// Package fdchannel implements passing file descriptors between processes over
+// Unix domain sockets.
+package fdchannel
+
+import (
+	"fmt"
+	"reflect"
+	"sync/atomic"
+	"syscall"
+	"unsafe"
+)
+
+// int32 is the real type of a file descriptor.
+const sizeofInt32 = int(unsafe.Sizeof(int32(0)))
+
+// NewConnectedSockets returns a pair of file descriptors, owned by the caller,
+// representing connected sockets that may be passed to separate calls to
+// NewEndpoint to create connected Endpoints.
+func NewConnectedSockets() ([2]int, error) {
+	return syscall.Socketpair(syscall.AF_UNIX, syscall.SOCK_SEQPACKET|syscall.SOCK_CLOEXEC, 0)
+}
+
+// Endpoint sends file descriptors to, and receives them from, another
+// connected Endpoint.
+//
+// Endpoint is not copyable or movable by value.
+type Endpoint struct {
+	sockfd int32 // accessed using atomic memory operations
+	msghdr syscall.Msghdr
+	cmsg   *syscall.Cmsghdr // followed by sizeofInt32 bytes of data
+}
+
+// Init must be called on zero-value Endpoints before first use. sockfd must be
+// a blocking AF_UNIX SOCK_SEQPACKET socket.
+func (ep *Endpoint) Init(sockfd int) {
+	// "Datagram sockets in various domains (e.g., the UNIX and Internet
+	// domains) permit zero-length datagrams." - recv(2). Experimentally,
+	// sendmsg+recvmsg for a zero-length datagram is slightly faster than
+	// sendmsg+recvmsg for a single byte over a stream socket.
+	cmsgSlice := make([]byte, syscall.CmsgSpace(sizeofInt32))
+	cmsgReflect := (*reflect.SliceHeader)((unsafe.Pointer)(&cmsgSlice))
+	ep.sockfd = int32(sockfd)
+	ep.msghdr.Control = (*byte)((unsafe.Pointer)(cmsgReflect.Data))
+	ep.cmsg = (*syscall.Cmsghdr)((unsafe.Pointer)(cmsgReflect.Data))
+	// ep.msghdr.Controllen and ep.cmsg.* are mutated by recvmsg(2), so they're
+	// set before calling sendmsg/recvmsg.
+}
+
+// NewEndpoint is a convenience function that returns an initialized Endpoint
+// allocated on the heap.
+func NewEndpoint(sockfd int) *Endpoint {
+	ep := &Endpoint{}
+	ep.Init(sockfd)
+	return ep
+}
+
+// Destroy releases resources owned by ep. No other Endpoint methods may be
+// called after Destroy.
+func (ep *Endpoint) Destroy() {
+	// These need not use sync/atomic since there must not be any concurrent
+	// calls to Endpoint methods.
+	if ep.sockfd >= 0 {
+		syscall.Close(int(ep.sockfd))
+		ep.sockfd = -1
+	}
+}
+
+// Shutdown causes concurrent and future calls to ep.SendFD(), ep.RecvFD(), and
+// ep.RecvFDNonblock(), as well as the same calls in the connected Endpoint, to
+// unblock and return errors. It does not wait for concurrent calls to return.
+//
+// Shutdown is the only Endpoint method that may be called concurrently with
+// other methods.
+func (ep *Endpoint) Shutdown() {
+	if sockfd := int(atomic.SwapInt32(&ep.sockfd, -1)); sockfd >= 0 {
+		syscall.Shutdown(sockfd, syscall.SHUT_RDWR)
+		syscall.Close(sockfd)
+	}
+}
+
+// SendFD sends the open file description represented by the given file
+// descriptor to the connected Endpoint.
+func (ep *Endpoint) SendFD(fd int) error {
+	cmsgLen := syscall.CmsgLen(sizeofInt32)
+	ep.cmsg.Level = syscall.SOL_SOCKET
+	ep.cmsg.Type = syscall.SCM_RIGHTS
+	ep.cmsg.SetLen(cmsgLen)
+	*ep.cmsgData() = int32(fd)
+	ep.msghdr.SetControllen(cmsgLen)
+	_, _, e := syscall.Syscall(syscall.SYS_SENDMSG, uintptr(atomic.LoadInt32(&ep.sockfd)), uintptr((unsafe.Pointer)(&ep.msghdr)), 0)
+	if e != 0 {
+		return e
+	}
+	return nil
+}
+
+// RecvFD receives an open file description from the connected Endpoint and
+// returns a file descriptor representing it, owned by the caller.
+func (ep *Endpoint) RecvFD() (int, error) {
+	return ep.recvFD(0)
+}
+
+// RecvFDNonblock receives an open file description from the connected Endpoint
+// and returns a file descriptor representing it, owned by the caller. If there
+// are no pending receivable open file descriptions, RecvFDNonblock returns
+// (<unspecified>, EAGAIN or EWOULDBLOCK).
+func (ep *Endpoint) RecvFDNonblock() (int, error) {
+	return ep.recvFD(syscall.MSG_DONTWAIT)
+}
+
+func (ep *Endpoint) recvFD(flags uintptr) (int, error) {
+	cmsgLen := syscall.CmsgLen(sizeofInt32)
+	ep.msghdr.SetControllen(cmsgLen)
+	_, _, e := syscall.Syscall(syscall.SYS_RECVMSG, uintptr(atomic.LoadInt32(&ep.sockfd)), uintptr((unsafe.Pointer)(&ep.msghdr)), flags|syscall.MSG_TRUNC)
+	if e != 0 {
+		return -1, e
+	}
+	if int(ep.msghdr.Controllen) != cmsgLen {
+		return -1, fmt.Errorf("received control message has incorrect length: got %d, wanted %d", ep.msghdr.Controllen, cmsgLen)
+	}
+	if ep.cmsg.Level != syscall.SOL_SOCKET || ep.cmsg.Type != syscall.SCM_RIGHTS {
+		return -1, fmt.Errorf("received control message has incorrect (level, type): got (%v, %v), wanted (%v, %v)", ep.cmsg.Level, ep.cmsg.Type, syscall.SOL_SOCKET, syscall.SCM_RIGHTS)
+	}
+	return int(*ep.cmsgData()), nil
+}
+
+func (ep *Endpoint) cmsgData() *int32 {
+	// syscall.CmsgLen(0) == syscall.cmsgAlignOf(syscall.SizeofCmsghdr)
+	return (*int32)((unsafe.Pointer)(uintptr((unsafe.Pointer)(ep.cmsg)) + uintptr(syscall.CmsgLen(0))))
+}