Add support for using PACKET_RX_RING to receive packets.

PACKET_RX_RING allows the use of an mmapped buffer to receive packets from the
kernel. This should cut down the number of host syscalls that need to be made
to receive packets when the underlying fd is a socket of the AF_PACKET type.

PiperOrigin-RevId: 233834998
Change-Id: I8060025c6ced206986e94cc46b8f382b81bfa47f

4 files changed, 24 insertions, 21 deletions

diff --git a/pkg/tcpip/link/rawfile/blockingpoll_amd64.s b/pkg/tcpip/link/rawfile/blockingpoll_amd64.s
index 8e22ba661..9dade5421 100644
--- a/pkg/tcpip/link/rawfile/blockingpoll_amd64.s
+++ b/pkg/tcpip/link/rawfile/blockingpoll_amd64.s
@@ -14,12 +14,12 @@
 
 #include "textflag.h"
 
-// blockingPoll makes the poll() syscall while calling the version of
+// BlockingPoll makes the poll() syscall while calling the version of
 // entersyscall that relinquishes the P so that other Gs can run. This is meant
 // to be called in cases when the syscall is expected to block.
 //
-// func blockingPoll(fds *pollEvent, nfds int, timeout int64) (n int, err syscall.Errno)
-TEXT ·blockingPoll(SB),NOSPLIT,$0-40
+// func BlockingPoll(fds *PollEvent, nfds int, timeout int64) (n int, err syscall.Errno)
+TEXT ·BlockingPoll(SB),NOSPLIT,$0-40
 	CALL	·callEntersyscallblock(SB)
 	MOVQ	fds+0(FP), DI
 	MOVQ	nfds+8(FP), SI
diff --git a/pkg/tcpip/link/rawfile/blockingpoll_amd64_unsafe.go b/pkg/tcpip/link/rawfile/blockingpoll_amd64_unsafe.go
index 93479cd0d..3ba96a123 100644
--- a/pkg/tcpip/link/rawfile/blockingpoll_amd64_unsafe.go
+++ b/pkg/tcpip/link/rawfile/blockingpoll_amd64_unsafe.go
@@ -25,7 +25,7 @@ import (
 )
 
 //go:noescape
-func blockingPoll(fds *pollEvent, nfds int, timeout int64) (int, syscall.Errno)
+func BlockingPoll(fds *PollEvent, nfds int, timeout int64) (int, syscall.Errno)
 
 // Use go:linkname to call into the runtime. As of Go 1.12 this has to
 // be done from Go code so that we make an ABIInternal call to an
diff --git a/pkg/tcpip/link/rawfile/blockingpoll_unsafe.go b/pkg/tcpip/link/rawfile/blockingpoll_unsafe.go
index 6a3e956ad..94ddad8ea 100644
--- a/pkg/tcpip/link/rawfile/blockingpoll_unsafe.go
+++ b/pkg/tcpip/link/rawfile/blockingpoll_unsafe.go
@@ -21,7 +21,9 @@ import (
 	"unsafe"
 )
 
-func blockingPoll(fds *pollEvent, nfds int, timeout int64) (int, syscall.Errno) {
+// BlockingPoll is just a stub function that forwards to the poll() system call
+// on non-amd64 platforms.
+func BlockingPoll(fds *PollEvent, nfds int, timeout int64) (int, syscall.Errno) {
 	n, _, e := syscall.Syscall(syscall.SYS_POLL, uintptr(unsafe.Pointer(fds)), uintptr(nfds), uintptr(timeout))
 	return int(n), e
 }
diff --git a/pkg/tcpip/link/rawfile/rawfile_unsafe.go b/pkg/tcpip/link/rawfile/rawfile_unsafe.go
index 5deea093a..5d36ebe57 100644
--- a/pkg/tcpip/link/rawfile/rawfile_unsafe.go
+++ b/pkg/tcpip/link/rawfile/rawfile_unsafe.go
@@ -94,10 +94,11 @@ func NonBlockingWrite2(fd int, b1, b2 []byte) *tcpip.Error {
 	return nil
 }
 
-type pollEvent struct {
-	fd      int32
-	events  int16
-	revents int16
+// PollEvent represents the pollfd structure passed to a poll() system call.
+type PollEvent struct {
+	FD      int32
+	Events  int16
+	Revents int16
 }
 
 // BlockingRead reads from a file descriptor that is set up as non-blocking. If
@@ -110,12 +111,12 @@ func BlockingRead(fd int, b []byte) (int, *tcpip.Error) {
 			return int(n), nil
 		}
 
-		event := pollEvent{
-			fd:     int32(fd),
-			events: 1, // POLLIN
+		event := PollEvent{
+			FD:     int32(fd),
+			Events: 1, // POLLIN
 		}
 
-		_, e = blockingPoll(&event, 1, -1)
+		_, e = BlockingPoll(&event, 1, -1)
 		if e != 0 && e != syscall.EINTR {
 			return 0, TranslateErrno(e)
 		}
@@ -132,12 +133,12 @@ func BlockingReadv(fd int, iovecs []syscall.Iovec) (int, *tcpip.Error) {
 			return int(n), nil
 		}
 
-		event := pollEvent{
-			fd:     int32(fd),
-			events: 1, // POLLIN
+		event := PollEvent{
+			FD:     int32(fd),
+			Events: 1, // POLLIN
 		}
 
-		_, e = blockingPoll(&event, 1, -1)
+		_, e = BlockingPoll(&event, 1, -1)
 		if e != 0 && e != syscall.EINTR {
 			return 0, TranslateErrno(e)
 		}
@@ -162,12 +163,12 @@ func BlockingRecvMMsg(fd int, msgHdrs []MMsgHdr) (int, *tcpip.Error) {
 			return int(n), nil
 		}
 
-		event := pollEvent{
-			fd:     int32(fd),
-			events: 1, // POLLIN
+		event := PollEvent{
+			FD:     int32(fd),
+			Events: 1, // POLLIN
 		}
 
-		if _, e := blockingPoll(&event, 1, -1); e != 0 && e != syscall.EINTR {
+		if _, e := BlockingPoll(&event, 1, -1); e != 0 && e != syscall.EINTR {
 			return 0, TranslateErrno(e)
 		}
 	}