Mypal/xpcom/glue/FileUtils.h

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* 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 "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) {
      while (close(aFd) == -1 && errno == EINTR) {
      }
    }
  }
};
typedef Scoped<ScopedCloseFDTraits> ScopedClose;

#if !defined(XPCOM_GLUE)

/**
 * 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);

#endif // !defined(XPCOM_GLUE)

/**
 * 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);


#if defined(XP_UNIX)
#define MOZ_TEMP_FAILURE_RETRY(exp) (__extension__({ \
  typeof (exp) _rc; \
  do { \
    _rc = (exp); \
  } while (_rc == -1 && errno == EINTR); \
  _rc; \
}))
#endif

/* Define ReadSysFile() and WriteSysFile() only in debug builds, so that 
 * unit tests for it can be written and run. */
#if defined(DEBUG) && defined(XP_UNIX)

#ifndef ReadSysFile_PRESENT
#define ReadSysFile_PRESENT
#endif /* ReadSysFile_PRESENT */

#ifndef WriteSysFile_PRESENT
#define WriteSysFile_PRESENT
#endif /* WriteSysFile_PRESENT */

/**
 * Read the contents of a file.
 * This function is intended for reading a single-lined text files from
 * /sys/. If the file ends with a newline ('\n') then it will be discarded.
 * The output buffer will always be '\0'-terminated on successful completion.
 * If aBufSize == 0, then this function will return true if the file exists
 * and is readable (it will not attempt to read anything from it).
 * On failure the contents of aBuf after this call will be undefined and the
 * value of the global variable errno will be set accordingly.
 * @return true on success, notice that less than requested bytes could have
 * been read if the file was smaller
 */
bool ReadSysFile(const char* aFilename, char* aBuf, size_t aBufSize);

/**
 * Parse the contents of a file, assuming it contains a decimal integer.
 * @return true on success
 */
bool ReadSysFile(const char* aFilename, int* aVal);

/**
 * Parse the contents of a file, assuming it contains a boolean value
 * (either 0 or 1).
 * @return true on success
 */
bool ReadSysFile(const char* aFilename, bool* aVal);

bool WriteSysFile(const char* aFilename, const char* aBuf);

#endif /* DEBUG && XP_UNIX */

} // namespace mozilla

#endif