jffs2: Fix segmentation fault found in stress test
[linux-3.10.git] / fs / jffs2 / compr_rtime.c
1 /*
2  * JFFS2 -- Journalling Flash File System, Version 2.
3  *
4  * Copyright © 2001-2007 Red Hat, Inc.
5  * Copyright © 2004-2010 David Woodhouse <dwmw2@infradead.org>
6  *
7  * Created by Arjan van de Ven <arjanv@redhat.com>
8  *
9  * For licensing information, see the file 'LICENCE' in this directory.
10  *
11  *
12  *
13  * Very simple lz77-ish encoder.
14  *
15  * Theory of operation: Both encoder and decoder have a list of "last
16  * occurrences" for every possible source-value; after sending the
17  * first source-byte, the second byte indicated the "run" length of
18  * matches
19  *
20  * The algorithm is intended to only send "whole bytes", no bit-messing.
21  *
22  */
23
24 #include <linux/kernel.h>
25 #include <linux/types.h>
26 #include <linux/errno.h>
27 #include <linux/string.h>
28 #include <linux/jffs2.h>
29 #include "compr.h"
30
31 /* _compress returns the compressed size, -1 if bigger */
32 static int jffs2_rtime_compress(unsigned char *data_in,
33                                 unsigned char *cpage_out,
34                                 uint32_t *sourcelen, uint32_t *dstlen)
35 {
36         unsigned short positions[256];
37         int outpos = 0;
38         int pos=0;
39
40         memset(positions,0,sizeof(positions));
41
42         while (pos < (*sourcelen) && outpos <= (*dstlen)-2) {
43                 int backpos, runlen=0;
44                 unsigned char value;
45
46                 value = data_in[pos];
47
48                 cpage_out[outpos++] = data_in[pos++];
49
50                 backpos = positions[value];
51                 positions[value]=pos;
52
53                 while ((backpos < pos) && (pos < (*sourcelen)) &&
54                        (data_in[pos]==data_in[backpos++]) && (runlen<255)) {
55                         pos++;
56                         runlen++;
57                 }
58                 cpage_out[outpos++] = runlen;
59         }
60
61         if (outpos >= pos) {
62                 /* We failed */
63                 return -1;
64         }
65
66         /* Tell the caller how much we managed to compress, and how much space it took */
67         *sourcelen = pos;
68         *dstlen = outpos;
69         return 0;
70 }
71
72
73 static int jffs2_rtime_decompress(unsigned char *data_in,
74                                   unsigned char *cpage_out,
75                                   uint32_t srclen, uint32_t destlen)
76 {
77         unsigned short positions[256];
78         int outpos = 0;
79         int pos=0;
80
81         memset(positions,0,sizeof(positions));
82
83         while (outpos<destlen) {
84                 unsigned char value;
85                 int backoffs;
86                 int repeat;
87
88                 value = data_in[pos++];
89                 cpage_out[outpos++] = value; /* first the verbatim copied byte */
90                 repeat = data_in[pos++];
91                 backoffs = positions[value];
92
93                 positions[value]=outpos;
94                 if (repeat) {
95                         if (backoffs + repeat >= outpos) {
96                                 while(repeat) {
97                                         cpage_out[outpos++] = cpage_out[backoffs++];
98                                         repeat--;
99                                 }
100                         } else {
101                                 memcpy(&cpage_out[outpos],&cpage_out[backoffs],repeat);
102                                 outpos+=repeat;
103                         }
104                 }
105         }
106         return 0;
107 }
108
109 static struct jffs2_compressor jffs2_rtime_comp = {
110     .priority = JFFS2_RTIME_PRIORITY,
111     .name = "rtime",
112     .compr = JFFS2_COMPR_RTIME,
113     .compress = &jffs2_rtime_compress,
114     .decompress = &jffs2_rtime_decompress,
115 #ifdef JFFS2_RTIME_DISABLED
116     .disabled = 1,
117 #else
118     .disabled = 0,
119 #endif
120 };
121
122 int jffs2_rtime_init(void)
123 {
124     return jffs2_register_compressor(&jffs2_rtime_comp);
125 }
126
127 void jffs2_rtime_exit(void)
128 {
129     jffs2_unregister_compressor(&jffs2_rtime_comp);
130 }