gecko-dev/xpcom/glue/FileUtils.h

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef mozilla_FileUtils_h
#define mozilla_FileUtils_h

#include "nscore.h"  // nullptr

#if defined(XP_UNIX)
#  include <unistd.h>
#elif defined(XP_WIN)
#  include <io.h>
#endif
#include "prio.h"
#include "prlink.h"

#include "mozilla/Scoped.h"
#include "nsIFile.h"
#include <errno.h>
#include <limits.h>

namespace mozilla {

#if defined(XP_WIN)
typedef void* filedesc_t;
typedef const wchar_t* pathstr_t;
#else
typedef int filedesc_t;
typedef const char* pathstr_t;
#endif

/**
 * ScopedCloseFD is a RAII wrapper for POSIX file descriptors
 *
 * Instances |close()| their fds when they go out of scope.
 */
struct ScopedCloseFDTraits {
  typedef int type;
  static type empty() { return -1; }
  static void release(type aFd) {
    if (aFd != -1) {
      close(aFd);
    }
  }
};
typedef Scoped<ScopedCloseFDTraits> ScopedClose;

#if defined(MOZILLA_INTERNAL_API)

/**
 * AutoFDClose is a RAII wrapper for PRFileDesc.
 *
 * Instances |PR_Close| their fds when they go out of scope.
 **/
struct ScopedClosePRFDTraits {
  typedef PRFileDesc* type;
  static type empty() { return nullptr; }
  static void release(type aFd) {
    if (aFd) {
      PR_Close(aFd);
    }
  }
};
typedef Scoped<ScopedClosePRFDTraits> AutoFDClose;

/* RAII wrapper for FILE descriptors */
struct ScopedCloseFileTraits {
  typedef FILE* type;
  static type empty() { return nullptr; }
  static void release(type aFile) {
    if (aFile) {
      fclose(aFile);
    }
  }
};
typedef Scoped<ScopedCloseFileTraits> ScopedCloseFile;

/**
 * Fallocate efficiently and continuously allocates files via fallocate-type
 * APIs. This is useful for avoiding fragmentation. On sucess the file be padded
 * with zeros to grow to aLength.
 *
 * @param aFD file descriptor.
 * @param aLength length of file to grow to.
 * @return true on success.
 */
bool fallocate(PRFileDesc* aFD, int64_t aLength);

/**
 * Use readahead to preload shared libraries into the file cache before loading.
 * WARNING: This function should not be used without a telemetry field trial
 *          demonstrating a clear performance improvement!
 *
 * @param aFile nsIFile representing path to shared library
 */
void ReadAheadLib(nsIFile* aFile);

/**
 * Use readahead to preload a file into the file cache before reading.
 * WARNING: This function should not be used without a telemetry field trial
 *          demonstrating a clear performance improvement!
 *
 * @param aFile nsIFile representing path to shared library
 * @param aOffset Offset into the file to begin preloading
 * @param aCount Number of bytes to preload (SIZE_MAX implies file size)
 * @param aOutFd Pointer to file descriptor. If specified, ReadAheadFile will
 *        return its internal, opened file descriptor instead of closing it.
 */
void ReadAheadFile(nsIFile* aFile, const size_t aOffset = 0,
                   const size_t aCount = SIZE_MAX,
                   filedesc_t* aOutFd = nullptr);

/*
 * Wrappers for PR_GetLibraryName and PR_GetLibraryFilePathname.
 */
PathString GetLibraryName(pathstr_t aDirectory, const char* aLib);
PathString GetLibraryFilePathname(pathstr_t aName, PRFuncPtr aAddr);

#endif  // MOZILLA_INTERNAL_API

/**
 * Use readahead to preload shared libraries into the file cache before loading.
 * WARNING: This function should not be used without a telemetry field trial
 *          demonstrating a clear performance improvement!
 *
 * @param aFilePath path to shared library
 */
void ReadAheadLib(pathstr_t aFilePath);

/**
 * Use readahead to preload a file into the file cache before loading.
 * WARNING: This function should not be used without a telemetry field trial
 *          demonstrating a clear performance improvement!
 *
 * @param aFilePath path to shared library
 * @param aOffset Offset into the file to begin preloading
 * @param aCount Number of bytes to preload (SIZE_MAX implies file size)
 * @param aOutFd Pointer to file descriptor. If specified, ReadAheadFile will
 *        return its internal, opened file descriptor instead of closing it.
 */
void ReadAheadFile(pathstr_t aFilePath, const size_t aOffset = 0,
                   const size_t aCount = SIZE_MAX,
                   filedesc_t* aOutFd = nullptr);

/**
 * Use readahead to preload a file into the file cache before reading.
 * When this function exits, the file pointer is guaranteed to be in the same
 * position it was in before this function was called.
 * WARNING: This function should not be used without a telemetry field trial
 *          demonstrating a clear performance improvement!
 *
 * @param aFd file descriptor opened for read access
 * (on Windows, file must be opened with FILE_FLAG_SEQUENTIAL_SCAN)
 * @param aOffset Offset into the file to begin preloading
 * @param aCount Number of bytes to preload (SIZE_MAX implies file size)
 */
void ReadAhead(filedesc_t aFd, const size_t aOffset = 0,
               const size_t aCount = SIZE_MAX);

}  // namespace mozilla

#endif