1 /* Copyright 2021 Alain Knaff.
2 * This file is part of mtools.
3 *
4 * Mtools 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, either version 3 of the License, or
7 * (at your option) any later version.
8 *
9 * Mtools is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with Mtools. If not, see <http://www.gnu.org/licenses/>.
16 *
17 * filter to support byte-swapped filesystems
18 */
19
20 #include "sysincludes.h"
21 #include "msdos.h"
22 #include "mtools.h"
23 #include "swap.h"
24
25 typedef struct Swap_t {
26 struct Stream_t head;
27 } Swap_t;
28
swap_buffer(char * buf,size_t len)29 static void swap_buffer(char *buf, size_t len)
30 {
31 unsigned int i;
32 for (i=0; i<len; i+=2) {
33 char temp = buf[i];
34 buf[i] = buf[i+1];
35 buf[i+1] = temp;
36 }
37 }
38
39
swap_pread(Stream_t * Stream,char * buf,mt_off_t where,size_t len)40 static ssize_t swap_pread(Stream_t *Stream, char *buf,
41 mt_off_t where, size_t len)
42 {
43 DeclareThis(Swap_t);
44
45 ssize_t result = PREADS(This->head.Next, buf, where, len);
46 if(result < 0)
47 return result;
48 swap_buffer( buf, (size_t) result);
49 return result;
50 }
51
swap_pwrite(Stream_t * Stream,char * buf,mt_off_t where,size_t len)52 static ssize_t swap_pwrite(Stream_t *Stream, char *buf,
53 mt_off_t where, size_t len)
54 {
55 DeclareThis(Swap_t);
56
57 ssize_t result;
58 char *swapping = malloc( len );
59 memcpy( swapping, buf, len );
60 swap_buffer( swapping, len );
61
62 result = PWRITES(This->head.Next, swapping, where, len);
63
64 free(swapping);
65 return result;
66 }
67
68
69 static Class_t SwapClass = {
70 0,
71 0,
72 swap_pread,
73 swap_pwrite,
74 0, /* flush */
75 0, /* free */
76 set_geom_pass_through, /* set_geom */
77 0, /* get_data */
78 0, /* pre-allocate */
79 get_dosConvert_pass_through, /* dos convert */
80 0, /* discard */
81 };
82
OpenSwap(Stream_t * Next)83 Stream_t *OpenSwap(Stream_t *Next) {
84 Swap_t *This;
85
86 This = New(Swap_t);
87 if (!This){
88 printOom();
89 return 0;
90 }
91 memset((void*)This, 0, sizeof(Swap_t));
92 init_head(&This->head, &SwapClass, Next);
93
94 return &This->head;
95 }
96