github.com/google/netstack@v0.0.0-20191123085552-55fcc16cd0eb/tcpip/link/fdbased/mmap_unsafe.go (about)

     1  // Copyright 2019 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  // +build linux,amd64 linux,arm64
    16  
    17  package fdbased
    18  
    19  import (
    20  	"fmt"
    21  	"sync/atomic"
    22  	"syscall"
    23  	"unsafe"
    24  
    25  	"golang.org/x/sys/unix"
    26  )
    27  
    28  // tPacketHdrlen is the TPACKET_HDRLEN variable defined in <linux/if_packet.h>.
    29  var tPacketHdrlen = tPacketAlign(unsafe.Sizeof(tPacketHdr{}) + unsafe.Sizeof(syscall.RawSockaddrLinklayer{}))
    30  
    31  // tpStatus returns the frame status field.
    32  // The status is concurrently updated by the kernel as a result we must
    33  // use atomic operations to prevent races.
    34  func (t tPacketHdr) tpStatus() uint32 {
    35  	hdr := unsafe.Pointer(&t[0])
    36  	statusPtr := unsafe.Pointer(uintptr(hdr) + uintptr(tpStatusOffset))
    37  	return atomic.LoadUint32((*uint32)(statusPtr))
    38  }
    39  
    40  // setTPStatus set's the frame status to the provided status.
    41  // The status is concurrently updated by the kernel as a result we must
    42  // use atomic operations to prevent races.
    43  func (t tPacketHdr) setTPStatus(status uint32) {
    44  	hdr := unsafe.Pointer(&t[0])
    45  	statusPtr := unsafe.Pointer(uintptr(hdr) + uintptr(tpStatusOffset))
    46  	atomic.StoreUint32((*uint32)(statusPtr), status)
    47  }
    48  
    49  func newPacketMMapDispatcher(fd int, e *endpoint) (linkDispatcher, error) {
    50  	d := &packetMMapDispatcher{
    51  		fd: fd,
    52  		e:  e,
    53  	}
    54  	pageSize := unix.Getpagesize()
    55  	if tpBlockSize%pageSize != 0 {
    56  		return nil, fmt.Errorf("tpBlockSize: %d is not page aligned, pagesize: %d", tpBlockSize, pageSize)
    57  	}
    58  	tReq := tPacketReq{
    59  		tpBlockSize: uint32(tpBlockSize),
    60  		tpBlockNR:   uint32(tpBlockNR),
    61  		tpFrameSize: uint32(tpFrameSize),
    62  		tpFrameNR:   uint32(tpFrameNR),
    63  	}
    64  	// Setup PACKET_RX_RING.
    65  	if err := setsockopt(d.fd, syscall.SOL_PACKET, syscall.PACKET_RX_RING, unsafe.Pointer(&tReq), unsafe.Sizeof(tReq)); err != nil {
    66  		return nil, fmt.Errorf("failed to enable PACKET_RX_RING: %v", err)
    67  	}
    68  	// Let's mmap the blocks.
    69  	sz := tpBlockSize * tpBlockNR
    70  	buf, err := syscall.Mmap(d.fd, 0, sz, syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_SHARED)
    71  	if err != nil {
    72  		return nil, fmt.Errorf("syscall.Mmap(...,0, %v, ...) failed = %v", sz, err)
    73  	}
    74  	d.ringBuffer = buf
    75  	return d, nil
    76  }
    77  
    78  func setsockopt(fd, level, name int, val unsafe.Pointer, vallen uintptr) error {
    79  	if _, _, errno := syscall.Syscall6(syscall.SYS_SETSOCKOPT, uintptr(fd), uintptr(level), uintptr(name), uintptr(val), vallen, 0); errno != 0 {
    80  		return error(errno)
    81  	}
    82  
    83  	return nil
    84  }