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/* 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 bzero'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, byte *buff, my_off_t pos, uint length,
int flag)
{
uint read_length,in_buff_length;
my_off_t offset;
char *in_buff_pos;
DBUG_ENTER("_mi_read_cache");
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)))
DBUG_RETURN(1);
if (!(length-=read_length))
DBUG_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,(uint) (info->read_end-in_buff_pos));
memcpy(buff,info->request_pos+(uint) offset,(size_t) in_buff_length);
if (!(length-=in_buff_length))
DBUG_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))
DBUG_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)
DBUG_RETURN(0);
}
if (!(flag & READING_HEADER) || (int) read_length == -1 ||
read_length+in_buff_length < 3)
{
DBUG_PRINT("error",
("Error %d reading next-multi-part block (Got %d bytes)",
my_errno, (int) read_length));
if (!my_errno || my_errno == -1)
my_errno=HA_ERR_WRONG_IN_RECORD;
DBUG_RETURN(1);
}
bzero(buff+read_length,MI_BLOCK_INFO_HEADER_LENGTH - in_buff_length -
read_length);
DBUG_RETURN(0);
} /* _mi_read_cache */
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