lib/crc32_file.c

/* Compute CRC32 checksum of file contents.
   Copyright (C) 2006 Red Hat, Inc.
   This file is part of Red Hat elfutils.

   Red Hat elfutils is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by the
   Free Software Foundation; version 2 of the License.

   Red Hat elfutils is distributed in the hope that it will be useful, but
   WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   General Public License for more details.

   You should have received a copy of the GNU General Public License along
   with Red Hat elfutils; if not, write to the Free Software Foundation,
   Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301 USA.

   In addition, as a special exception, Red Hat, Inc. gives You the
   additional right to link the code of Red Hat elfutils with code licensed
   under an Open Source Initiative certified open source license
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   exception must only link to the code of Red Hat elfutils through those
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   this exception is conditioned upon your not adding any new exceptions.
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   for all of the Red Hat elfutils code and other code used in conjunction
   with Red Hat elfutils except the Non-GPL Code covered by this exception.
   If you modify this file, you may extend this exception to your version
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   the GPL without exception.

   Red Hat elfutils is an included package of the Open Invention Network.
   An included package of the Open Invention Network is a package for which
   Open Invention Network licensees cross-license their patents.  No patent
   license is granted, either expressly or impliedly, by designation as an
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#include "system.h"
#include <errno.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/mman.h>

int
crc32_file (int fd, uint32_t *resp)
{
  unsigned char buffer[1024 * 8];
  uint32_t crc = 0;
  off_t off = 0;
  ssize_t count;

  struct stat st;
  if (fstat (fd, &st) == 0)
    {
      /* Try mapping in the file data.  */
      size_t mapsize = st.st_size;
      void *mapped = mmap (NULL, mapsize, PROT_READ, MAP_PRIVATE, fd, 0);
      if (mapped == MAP_FAILED && errno == ENOMEM)
	{
	  const size_t pagesize = sysconf (_SC_PAGE_SIZE);
	  mapsize = ((mapsize / 2) + pagesize - 1) & -pagesize;
	  while (mapsize >= pagesize
		 && (mapped = mmap (NULL, mapsize, PROT_READ, MAP_PRIVATE,
				    fd, 0)) == MAP_FAILED && errno == ENOMEM)
	    mapsize /= 2;
	}
      if (mapped != MAP_FAILED)
	{
	  do
	    {
	      if (st.st_size <= (off_t) mapsize)
		{
		  *resp = crc32 (crc, mapped, st.st_size);
		  munmap (mapped, mapsize);
		  return 0;
		}
	      crc = crc32 (crc, mapped, mapsize);
	      off += mapsize;
	      st.st_size -= mapsize;
	    } while (mmap (mapped, mapsize, PROT_READ, MAP_FIXED|MAP_PRIVATE,
			   fd, off) == mapped);
	  munmap (mapped, mapsize);
	}
    }

  while ((count = TEMP_FAILURE_RETRY (pread (fd, buffer, sizeof buffer,
					     off))) > 0)
    {
      off += count;
      crc = crc32 (crc, buffer, count);
    }

  *resp = crc;

  return count == 0 ? 0 : -1;
}