1/* Copyright (c) 2000-2003, 2005-2007 MySQL AB, 2009 Sun Microsystems, Inc.
2 Use is subject to license terms.
3
4 This program is free software; you can redistribute it and/or modify
5 it under the terms of the GNU General Public License as published by
6 the Free Software Foundation; version 2 of the License.
7
8 This program is distributed in the hope that it will be useful,
9 but WITHOUT ANY WARRANTY; without even the implied warranty of
10 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
11 GNU General Public License for more details.
12
13 You should have received a copy of the GNU General Public License
14 along with this program; if not, write to the Free Software
15 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA */
16
17/*
18 Functions for read record cacheing with myisam
19 Used for reading dynamic/compressed records from datafile.
20
21 Can fetch data directly from file (outside cache),
22 if reading a small chunk straight before the cached part (with possible
23 overlap).
24
25 Can be explicitly asked not to use cache (by not setting READING_NEXT in
26 flag) - useful for occasional out-of-cache reads, when the next read is
27 expected to hit the cache again.
28
29 Allows "partial read" errors in the record header (when READING_HEADER flag
30 is set) - unread part is bzero'ed
31
32 Note: out-of-cache reads are enabled for shared IO_CACHE's too,
33 as these reads will be cached by OS cache (and mysql_file_pread is always atomic)
34*/
35
36#include "myisamdef.h"
37
38int _mi_read_cache(IO_CACHE *info, uchar *buff, my_off_t pos, size_t length,
39 int flag)
40{
41 size_t read_length,in_buff_length;
42 my_off_t offset;
43 uchar *in_buff_pos;
44 DBUG_ENTER("_mi_read_cache");
45 DBUG_ASSERT(!(info->myflags & MY_ENCRYPT));
46
47 if (pos < info->pos_in_file)
48 {
49 read_length=length;
50 if ((my_off_t) read_length > (my_off_t) (info->pos_in_file-pos))
51 read_length=(size_t)(info->pos_in_file-pos);
52 info->seek_not_done=1;
53 if (mysql_file_pread(info->file, buff, read_length, pos, MYF(MY_NABP)))
54 DBUG_RETURN(1);
55 if (!(length-=read_length))
56 DBUG_RETURN(0);
57 pos+=read_length;
58 buff+=read_length;
59 }
60 if (pos >= info->pos_in_file &&
61 (offset= (my_off_t) (pos - info->pos_in_file)) <
62 (my_off_t) (info->read_end - info->request_pos))
63 {
64 in_buff_pos=info->request_pos+ (uint)offset;
65 in_buff_length= MY_MIN(length, (size_t)(info->read_end-in_buff_pos));
66 memcpy(buff,info->request_pos+(uint) offset, in_buff_length);
67 if (!(length-=in_buff_length))
68 DBUG_RETURN(0);
69 pos+=in_buff_length;
70 buff+=in_buff_length;
71 }
72 else
73 in_buff_length=0;
74 if (flag & READING_NEXT)
75 {
76 if (pos != (info->pos_in_file +
77 (uint) (info->read_end - info->request_pos)))
78 {
79 info->pos_in_file=pos; /* Force start here */
80 info->read_pos=info->read_end=info->request_pos; /* Everything used */
81 info->seek_not_done=1;
82 }
83 else
84 info->read_pos=info->read_end; /* All block used */
85 if (!_my_b_read(info,buff,length))
86 DBUG_RETURN(0);
87 read_length=info->error;
88 }
89 else
90 {
91 info->seek_not_done=1;
92 if ((read_length= mysql_file_pread(info->file, buff, length, pos,
93 MYF(0))) == length)
94 DBUG_RETURN(0);
95 }
96 if (!(flag & READING_HEADER) || (int) read_length == -1 ||
97 read_length+in_buff_length < 3)
98 {
99 DBUG_PRINT("error",
100 ("Error %d reading next-multi-part block (Got %d bytes)",
101 my_errno, (int) read_length));
102 if (!my_errno || my_errno == -1 || my_errno == HA_ERR_FILE_TOO_SHORT)
103 my_errno= HA_ERR_WRONG_IN_RECORD;
104 DBUG_RETURN(1);
105 }
106 bzero(buff+read_length,MI_BLOCK_INFO_HEADER_LENGTH - in_buff_length -
107 read_length);
108 DBUG_RETURN(0);
109} /* _mi_read_cache */
110