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

     1  /*
     2   * Copyright 2020 Dgraph Labs, Inc. and Contributors
     3   *
     4   * Licensed under the Apache License, Version 2.0 (the "License");
     5   * you may not use this file except in compliance with the License.
     6   * You may obtain a copy of the License at
     7   *
     8   *     http://www.apache.org/licenses/LICENSE-2.0
     9   *
    10   * Unless required by applicable law or agreed to in writing, software
    11   * distributed under the License is distributed on an "AS IS" BASIS,
    12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13   * See the License for the specific language governing permissions and
    14   * limitations under the License.
    15   */
    16  
    17  package z
    18  
    19  import (
    20  	"os"
    21  	"unsafe"
    22  
    23  	"golang.org/x/sys/unix"
    24  )
    25  
    26  // mmap uses the mmap system call to memory-map a file. If writable is true,
    27  // memory protection of the pages is set so that they may be written to as well.
    28  func mmap(fd *os.File, writable bool, size int64) ([]byte, error) {
    29  	mtype := unix.PROT_READ
    30  	if writable {
    31  		mtype |= unix.PROT_WRITE
    32  	}
    33  	return unix.Mmap(int(fd.Fd()), 0, int(size), mtype, unix.MAP_SHARED)
    34  }
    35  
    36  // munmap unmaps a previously mapped slice.
    37  //
    38  // unix.Munmap maintains an internal list of mmapped addresses, and only calls munmap
    39  // if the address is present in that list. If we use mremap, this list is not updated.
    40  // To bypass this, we call munmap ourselves.
    41  func munmap(data []byte) error {
    42  	if len(data) == 0 || len(data) != cap(data) {
    43  		return unix.EINVAL
    44  	}
    45  	_, _, errno := unix.Syscall(
    46  		unix.SYS_MUNMAP,
    47  		uintptr(unsafe.Pointer(&data[0])),
    48  		uintptr(len(data)),
    49  		0,
    50  	)
    51  	if errno != 0 {
    52  		return errno
    53  	}
    54  	return nil
    55  }
    56  
    57  // madvise uses the madvise system call to give advise about the use of memory
    58  // when using a slice that is memory-mapped to a file. Set the readahead flag to
    59  // false if page references are expected in random order.
    60  func madvise(b []byte, readahead bool) error {
    61  	flags := unix.MADV_NORMAL
    62  	if !readahead {
    63  		flags = unix.MADV_RANDOM
    64  	}
    65  	return unix.Madvise(b, flags)
    66  }
    67  
    68  // msync writes any modified data to persistent storage.
    69  func msync(b []byte) error {
    70  	return unix.Msync(b, unix.MS_SYNC)
    71  }