Drizzled Public API Documentation

mi_cache.cc
1 /* Copyright (C) 2000-2003 MySQL AB
2 
3  This program is free software; you can redistribute it and/or modify
4  it under the terms of the GNU General Public License as published by
5  the Free Software Foundation; version 2 of the License.
6 
7  This program is distributed in the hope that it will be useful,
8  but WITHOUT ANY WARRANTY; without even the implied warranty of
9  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
10  GNU General Public License for more details.
11 
12  You should have received a copy of the GNU General Public License
13  along with this program; if not, write to the Free Software
14  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA */
15 
16 /*
17  Functions for read record cacheing with myisam
18  Used for reading dynamic/compressed records from datafile.
19 
20  Can fetch data directly from file (outside cache),
21  if reading a small chunk straight before the cached part (with possible
22  overlap).
23 
24  Can be explicitly asked not to use cache (by not setting READING_NEXT in
25  flag) - useful for occasional out-of-cache reads, when the next read is
26  expected to hit the cache again.
27 
28  Allows "partial read" errors in the record header (when READING_HEADER flag
29  is set) - unread part is zero'ed
30 
31  Note: out-of-cache reads are enabled for shared io_cache_st's too,
32  as these reads will be cached by OS cache (and my_pread is always atomic)
33 */
34 
35 
36 #include "myisam_priv.h"
37 
38 #include <algorithm>
39 
40 using namespace std;
41 using namespace drizzled;
42 
43 
44 int _mi_read_cache(internal::io_cache_st *info, unsigned char *buff, internal::my_off_t pos, uint32_t length,
45  int flag)
46 {
47  uint32_t read_length,in_buff_length;
48  internal::my_off_t offset;
49  unsigned char *in_buff_pos;
50 
51  if (pos < info->pos_in_file)
52  {
53  read_length=length;
54  if ((internal::my_off_t) read_length > (internal::my_off_t) (info->pos_in_file-pos))
55  read_length=(uint) (info->pos_in_file-pos);
56  info->seek_not_done=1;
57  if (my_pread(info->file,buff,read_length,pos,MYF(MY_NABP)))
58  return(1);
59  if (!(length-=read_length))
60  return(0);
61  pos+=read_length;
62  buff+=read_length;
63  }
64  if (pos >= info->pos_in_file &&
65  (offset= (internal::my_off_t) (pos - info->pos_in_file)) <
66  (internal::my_off_t) (info->read_end - info->request_pos))
67  {
68  in_buff_pos=info->request_pos+(uint) offset;
69  in_buff_length= min(length, (uint32_t) (info->read_end-in_buff_pos));
70  memcpy(buff,info->request_pos+(uint) offset,(size_t) in_buff_length);
71  if (!(length-=in_buff_length))
72  return(0);
73  pos+=in_buff_length;
74  buff+=in_buff_length;
75  }
76  else
77  in_buff_length=0;
78  if (flag & READING_NEXT)
79  {
80  if (pos != (info->pos_in_file +
81  (uint) (info->read_end - info->request_pos)))
82  {
83  info->pos_in_file=pos; /* Force start here */
84  info->read_pos=info->read_end=info->request_pos; /* Everything used */
85  info->seek_not_done=1;
86  }
87  else
88  info->read_pos=info->read_end; /* All block used */
89  if (!(*info->read_function)(info,buff,length))
90  return(0);
91  read_length=info->error;
92  }
93  else
94  {
95  info->seek_not_done=1;
96  if ((read_length=my_pread(info->file,buff,length,pos,MYF(0))) == length)
97  return(0);
98  }
99  if (!(flag & READING_HEADER) || (int) read_length == -1 ||
100  read_length+in_buff_length < 3)
101  {
102  if (!errno || errno == -1)
103  errno=HA_ERR_WRONG_IN_RECORD;
104  return(1);
105  }
106  memset(buff+read_length, 0,
107  MI_BLOCK_INFO_HEADER_LENGTH - in_buff_length - read_length);
108  return(0);
109 } /* _mi_read_cache */
TODO: Rename this file - func.h is stupid.