fallocate() Befehlsäquivalent in OS X?

Was ist mit der Verwendung von:

mkfile -n 1m test.tmp

Es ist nicht derselbe Befehl, dient aber demselben Zweck.

Beachten Sie, dass fallocate verwendet dezimale Multiplikatoren, während mkfile verwendet binäre Multiplikatoren.

mkfile man

Für diejenigen, die gefälschte Datendateien zum Testen erstellen möchten, mkfile ist ziemlich elegant. Eine Alternative ist die Verwendung von dd :

dd if=/dev/zero of=zfile count=1024 bs=1024

Wie Sie mit od -b zfile sehen können , es ist voller Nullen. Wenn Sie zufällige Daten wünschen (z. B. zum Testen von Workflows mit Datenkomprimierung), verwenden Sie „/dev/random“ anstelle von „/dev/zero“:

dd if=/dev/random of=randfile count=1024 bs=1024

fallocate() existiert nicht unter OSX. Sie können es jedoch "vortäuschen"; Mozilla fälscht es in ihrer FileUtils-Klasse. Siehe diese Datei:

http://hg.mozilla.org/mozilla-central/file/3d846420a907/xpcom/glue/FileUtils.cpp#l61

Hier ist der Code, falls dieser Link veraltet ist:

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 * ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (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.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is Mozilla code.
 *
 * The Initial Developer of the Original Code is
 * Mozilla Foundation.
 * Portions created by the Initial Developer are Copyright (C) 2010
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   Taras Glek <[email protected]>
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either the GNU General Public License Version 2 or later (the "GPL"), or
 * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
 * of those above. If you wish to allow use of your version of this file only
 * under the terms of either the GPL or the LGPL, and not to allow others to
 * use your version of this file under the terms of the MPL, indicate your
 * decision by deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL or the LGPL. If you do not delete
 * the provisions above, a recipient may use your version of this file under
 * the terms of any one of the MPL, the GPL or the LGPL.
 *
 * ***** END LICENSE BLOCK ***** */
#if defined(XP_UNIX)
#include <fcntl.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#elif defined(XP_WIN)
#include <windows.h>
#endif

#include "nscore.h"
#include "private/pprio.h"
#include "mozilla/FileUtils.h"

bool 
mozilla::fallocate(PRFileDesc *aFD, PRInt64 aLength) 
{
#if defined(HAVE_POSIX_FALLOCATE)
  return posix_fallocate(PR_FileDesc2NativeHandle(aFD), 0, aLength) == 0;
#elif defined(XP_WIN)
  return PR_Seek64(aFD, aLength, PR_SEEK_SET) == aLength
    && 0 != SetEndOfFile((HANDLE)PR_FileDesc2NativeHandle(aFD));
#elif defined(XP_MACOSX)
  int fd = PR_FileDesc2NativeHandle(aFD);
  fstore_t store = {F_ALLOCATECONTIG, F_PEOFPOSMODE, 0, aLength};
  // Try to get a continous chunk of disk space
  int ret = fcntl(fd, F_PREALLOCATE, &store);
    if(-1 == ret){
    // OK, perhaps we are too fragmented, allocate non-continuous
    store.fst_flags = F_ALLOCATEALL;
    ret = fcntl(fd, F_PREALLOCATE, &store);
    if (-1 == ret)
      return false;
  }
  return 0 == ftruncate(fd, aLength);
#elif defined(XP_UNIX)
  // The following is copied from fcntlSizeHint in sqlite
  /* If the OS does not have posix_fallocate(), fake it. First use
  ** ftruncate() to set the file size, then write a single byte to
  ** the last byte in each block within the extended region. This
  ** is the same technique used by glibc to implement posix_fallocate()
  ** on systems that do not have a real fallocate() system call.
  */
  struct stat buf;
  int fd = PR_FileDesc2NativeHandle(aFD);
  if (fstat(fd, &buf))
    return false;

  if (buf.st_size >= aLength)
    return false;

  const int nBlk = buf.st_blksize;

  if (!nBlk)
    return false;

  if (ftruncate(fd, aLength))
    return false;

  int nWrite; // Return value from write()
  PRInt64 iWrite = ((buf.st_size + 2 * nBlk - 1) / nBlk) * nBlk - 1; // Next offset to write to
  do {
    nWrite = 0;
    if (PR_Seek64(aFD, iWrite, PR_SEEK_SET) == iWrite)
      nWrite = PR_Write(aFD, "", 1);
    iWrite += nBlk;
  } while (nWrite == 1 && iWrite < aLength);
  return nWrite == 1;
#endif
  return false;
}