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go-library/vendor/github.com/dgraph-io/ristretto/z/mmap_linux.go

102 lines
2.8 KiB

/*
* Copyright 2020 Dgraph Labs, Inc. and Contributors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package z
import (
"fmt"
"os"
"reflect"
"unsafe"
"golang.org/x/sys/unix"
)
// mmap uses the mmap system call to memory-map a file. If writable is true,
// memory protection of the pages is set so that they may be written to as well.
func mmap(fd *os.File, writable bool, size int64) ([]byte, error) {
mtype := unix.PROT_READ
if writable {
mtype |= unix.PROT_WRITE
}
return unix.Mmap(int(fd.Fd()), 0, int(size), mtype, unix.MAP_SHARED)
}
// mremap is a Linux-specific system call to remap pages in memory. This can be used in place of munmap + mmap.
func mremap(data []byte, size int) ([]byte, error) {
// taken from <https://github.com/torvalds/linux/blob/f8394f232b1eab649ce2df5c5f15b0e528c92091/include/uapi/linux/mman.h#L8>
const MREMAP_MAYMOVE = 0x1
header := (*reflect.SliceHeader)(unsafe.Pointer(&data))
mmapAddr, mmapSize, errno := unix.Syscall6(
unix.SYS_MREMAP,
header.Data,
uintptr(header.Len),
uintptr(size),
uintptr(MREMAP_MAYMOVE),
0,
0,
)
if errno != 0 {
return nil, errno
}
if mmapSize != uintptr(size) {
return nil, fmt.Errorf("mremap size mismatch: requested: %d got: %d", size, mmapSize)
}
header.Data = mmapAddr
header.Cap = size
header.Len = size
return data, nil
}
// munmap unmaps a previously mapped slice.
//
// unix.Munmap maintains an internal list of mmapped addresses, and only calls munmap
// if the address is present in that list. If we use mremap, this list is not updated.
// To bypass this, we call munmap ourselves.
func munmap(data []byte) error {
if len(data) == 0 || len(data) != cap(data) {
return unix.EINVAL
}
_, _, errno := unix.Syscall(
unix.SYS_MUNMAP,
uintptr(unsafe.Pointer(&data[0])),
uintptr(len(data)),
0,
)
if errno != 0 {
return errno
}
return nil
}
// madvise uses the madvise system call to give advise about the use of memory
// when using a slice that is memory-mapped to a file. Set the readahead flag to
// false if page references are expected in random order.
func madvise(b []byte, readahead bool) error {
flags := unix.MADV_NORMAL
if !readahead {
flags = unix.MADV_RANDOM
}
return unix.Madvise(b, flags)
}
// msync writes any modified data to persistent storage.
func msync(b []byte) error {
return unix.Msync(b, unix.MS_SYNC)
}