github.com/fiatjaf/generic-ristretto@v0.0.1/z/mremap_linux.go (about)

     1  // +build !arm64
     2  
     3  /*
     4   * Copyright 2020 Dgraph Labs, Inc. and Contributors
     5   *
     6   * Licensed under the Apache License, Version 2.0 (the "License");
     7   * you may not use this file except in compliance with the License.
     8   * You may obtain a copy of the License at
     9   *
    10   *     http://www.apache.org/licenses/LICENSE-2.0
    11   *
    12   * Unless required by applicable law or agreed to in writing, software
    13   * distributed under the License is distributed on an "AS IS" BASIS,
    14   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    15   * See the License for the specific language governing permissions and
    16   * limitations under the License.
    17   */
    18  
    19  package z
    20  
    21  import (
    22  	"fmt"
    23  	"reflect"
    24  	"unsafe"
    25  
    26  	"golang.org/x/sys/unix"
    27  )
    28  
    29  // mremap is a Linux-specific system call to remap pages in memory. This can be used in place of munmap + mmap.
    30  func mremap(data []byte, size int) ([]byte, error) {
    31  	//nolint:lll
    32  	// taken from <https://github.com/torvalds/linux/blob/f8394f232b1eab649ce2df5c5f15b0e528c92091/include/uapi/linux/mman.h#L8>
    33  	const MREMAP_MAYMOVE = 0x1
    34  
    35  	header := (*reflect.SliceHeader)(unsafe.Pointer(&data))
    36  	mmapAddr, mmapSize, errno := unix.Syscall6(
    37  		unix.SYS_MREMAP,
    38  		header.Data,
    39  		uintptr(header.Len),
    40  		uintptr(size),
    41  		uintptr(MREMAP_MAYMOVE),
    42  		0,
    43  		0,
    44  	)
    45  	if errno != 0 {
    46  		return nil, errno
    47  	}
    48  	if mmapSize != uintptr(size) {
    49  		return nil, fmt.Errorf("mremap size mismatch: requested: %d got: %d", size, mmapSize)
    50  	}
    51  
    52  	header.Data = mmapAddr
    53  	header.Cap = size
    54  	header.Len = size
    55  	return data, nil
    56  }