folly/folly/system/MemoryMapping.h

/*
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * 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.
 */

#pragma once

#include <cassert>

#include <folly/File.h>
#include <folly/Range.h>
#include <folly/portability/Unistd.h>

namespace folly {

/**
 * Maps files in memory (read-only).
 */
class MemoryMapping { … };

void swap(MemoryMapping&, MemoryMapping&) noexcept;

/**
 * A special case of memcpy() that always copies memory forwards.
 * (libc's memcpy() is allowed to copy memory backwards, and will do so
 * when using SSSE3 instructions).
 *
 * Assumes src and dest are aligned to alignof(unsigned long).
 *
 * Useful when copying from/to memory mappings after hintLinearScan();
 * copying backwards renders any prefetching useless (even harmful).
 */
void alignedForwardMemcpy(void* dst, const void* src, size_t size);

/**
 * Copy a file using mmap(). Overwrites dest.
 */
void mmapFileCopy(const char* src, const char* dest, mode_t mode = 0666);

/**
 * mlock2 is Linux-only and exists since Linux 4.4
 * On Linux pre-4.4 and other platforms fail with ENOSYS.
 * glibc added the mlock2 wrapper in 2.27
 * https://lists.gnu.org/archive/html/info-gnu/2018-02/msg00000.html
 */
int mlock2wrapper(const void* addr, size_t len, MemoryMapping::LockFlags flags);

} // namespace folly