~drizzle-trunk/drizzle/development

/* Copyright (C) 2000-2003 MySQL AB

   This program 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.

   This program 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 this program; if not, write to the Free Software

   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */

/*

  Functions for read record cacheing with myisam

  Used for reading dynamic/compressed records from datafile.

  Can fetch data directly from file (outside cache),

  if reading a small chunk straight before the cached part (with possible

  overlap).

  Can be explicitly asked not to use cache (by not setting READING_NEXT in

  flag) - useful for occasional out-of-cache reads, when the next read is

  expected to hit the cache again.

  Allows "partial read" errors in the record header (when READING_HEADER flag

  is set) - unread part is zero'ed

  Note: out-of-cache reads are enabled for shared IO_CACHE's too,

  as these reads will be cached by OS cache (and my_pread is always atomic)

*/

#include "myisamdef.h"

int _mi_read_cache(IO_CACHE *info, uchar *buff, my_off_t pos, uint length,

		   int flag)

{

  uint read_length,in_buff_length;

  my_off_t offset;

  uchar *in_buff_pos;

  if (pos < info->pos_in_file)

  {

    read_length=length;

    if ((my_off_t) read_length > (my_off_t) (info->pos_in_file-pos))

      read_length=(uint) (info->pos_in_file-pos);

    info->seek_not_done=1;

    if (my_pread(info->file,buff,read_length,pos,MYF(MY_NABP)))

      return(1);

    if (!(length-=read_length))

      return(0);

    pos+=read_length;

    buff+=read_length;

  }

  if (pos >= info->pos_in_file &&

      (offset= (my_off_t) (pos - info->pos_in_file)) <

      (my_off_t) (info->read_end - info->request_pos))

  {

    in_buff_pos=info->request_pos+(uint) offset;

    in_buff_length= min(length, (size_t) (info->read_end-in_buff_pos));

    memcpy(buff,info->request_pos+(uint) offset,(size_t) in_buff_length);

    if (!(length-=in_buff_length))

      return(0);

    pos+=in_buff_length;

    buff+=in_buff_length;

  }

  else

    in_buff_length=0;

  if (flag & READING_NEXT)

  {

    if (pos != (info->pos_in_file +

		(uint) (info->read_end - info->request_pos)))

    {

      info->pos_in_file=pos;				/* Force start here */

      info->read_pos=info->read_end=info->request_pos;	/* Everything used */

      info->seek_not_done=1;

    }

    else

      info->read_pos=info->read_end;			/* All block used */

    if (!(*info->read_function)(info,buff,length))

      return(0);

    read_length=info->error;

  }

  else

  {

    info->seek_not_done=1;

    if ((read_length=my_pread(info->file,buff,length,pos,MYF(0))) == length)

      return(0);

  }

  if (!(flag & READING_HEADER) || (int) read_length == -1 ||

      read_length+in_buff_length < 3)

  {

    if (!my_errno || my_errno == -1)

      my_errno=HA_ERR_WRONG_IN_RECORD;

    return(1);

  }

  memset(buff+read_length, 0,

         MI_BLOCK_INFO_HEADER_LENGTH - in_buff_length - read_length);

  return(0);

} /* _mi_read_cache */