github.com/MerlinKodo/gvisor@v0.0.0-20231110090155-957f62ecf90e/pkg/tcpip/link/sharedmem/sharedmem_unsafe.go (about)

     1  // Copyright 2018 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  package sharedmem
    16  
    17  import (
    18  	"fmt"
    19  	"reflect"
    20  	"unsafe"
    21  
    22  	"github.com/MerlinKodo/gvisor/pkg/atomicbitops"
    23  	"github.com/MerlinKodo/gvisor/pkg/memutil"
    24  	"golang.org/x/sys/unix"
    25  )
    26  
    27  // sharedDataPointer converts the shared data slice into a pointer so that it
    28  // can be used in atomic operations.
    29  func sharedDataPointer(sharedData []byte) *atomicbitops.Uint32 {
    30  	return (*atomicbitops.Uint32)(unsafe.Pointer(&sharedData[0:4][0]))
    31  }
    32  
    33  // getBuffer returns a memory region mapped to the full contents of the given
    34  // file descriptor.
    35  func getBuffer(fd int) ([]byte, error) {
    36  	var s unix.Stat_t
    37  	if err := unix.Fstat(fd, &s); err != nil {
    38  		return nil, err
    39  	}
    40  
    41  	// Check that size doesn't overflow an int.
    42  	if s.Size > int64(^uint(0)>>1) {
    43  		return nil, unix.EDOM
    44  	}
    45  
    46  	addr, err := memutil.MapFile(0 /* addr */, uintptr(s.Size), unix.PROT_READ|unix.PROT_WRITE, unix.MAP_SHARED|unix.MAP_FILE, uintptr(fd), 0 /*offset*/)
    47  	if err != nil {
    48  		return nil, fmt.Errorf("failed to map memory for buffer fd: %d, error: %s", fd, err)
    49  	}
    50  
    51  	// Use unsafe to conver addr into a []byte.
    52  	var b []byte
    53  	hdr := (*reflect.SliceHeader)(unsafe.Pointer(&b))
    54  	hdr.Data = addr
    55  	hdr.Len = int(s.Size)
    56  	hdr.Cap = int(s.Size)
    57  
    58  	return b, nil
    59  }