1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * linux/fs/adfs/map.c
4 *
5 * Copyright (C) 1997-2002 Russell King
6 */
7 #include <asm/unaligned.h>
8 #include "adfs.h"
9
10 /*
11 * The ADFS map is basically a set of sectors. Each sector is called a
12 * zone which contains a bitstream made up of variable sized fragments.
13 * Each bit refers to a set of bytes in the filesystem, defined by
14 * log2bpmb. This may be larger or smaller than the sector size, but
15 * the overall size it describes will always be a round number of
16 * sectors. A fragment id is always idlen bits long.
17 *
18 * < idlen > < n > <1>
19 * +---------+-------//---------+---+
20 * | frag id | 0000....000000 | 1 |
21 * +---------+-------//---------+---+
22 *
23 * The physical disk space used by a fragment is taken from the start of
24 * the fragment id up to and including the '1' bit - ie, idlen + n + 1
25 * bits.
26 *
27 * A fragment id can be repeated multiple times in the whole map for
28 * large or fragmented files. The first map zone a fragment starts in
29 * is given by fragment id / ids_per_zone - this allows objects to start
30 * from any zone on the disk.
31 *
32 * Free space is described by a linked list of fragments. Each free
33 * fragment describes free space in the same way as the other fragments,
34 * however, the frag id specifies an offset (in map bits) from the end
35 * of this fragment to the start of the next free fragment.
36 *
37 * Objects stored on the disk are allocated object ids (we use these as
38 * our inode numbers.) Object ids contain a fragment id and an optional
39 * offset. This allows a directory fragment to contain small files
40 * associated with that directory.
41 */
42
43 /*
44 * For the future...
45 */
46 static DEFINE_RWLOCK(adfs_map_lock);
47
48 /*
49 * This is fun. We need to load up to 19 bits from the map at an
50 * arbitrary bit alignment. (We're limited to 19 bits by F+ version 2).
51 */
52 #define GET_FRAG_ID(_map,_start,_idmask) \
53 ({ \
54 unsigned char *_m = _map + (_start >> 3); \
55 u32 _frag = get_unaligned_le32(_m); \
56 _frag >>= (_start & 7); \
57 _frag & _idmask; \
58 })
59
60 /*
61 * return the map bit offset of the fragment frag_id in the zone dm.
62 * Note that the loop is optimised for best asm code - look at the
63 * output of:
64 * gcc -D__KERNEL__ -O2 -I../../include -o - -S map.c
65 */
66 static int lookup_zone(const struct adfs_discmap *dm, const unsigned int idlen,
67 const u32 frag_id, unsigned int *offset)
68 {
69 const unsigned int mapsize = dm->dm_endbit;
70 const u32 idmask = (1 << idlen) - 1;
71 unsigned char *map = dm->dm_bh->b_data + 4;
72 unsigned int start = dm->dm_startbit;
73 unsigned int mapptr;
74 u32 frag;
75
76 do {
77 frag = GET_FRAG_ID(map, start, idmask);
78 mapptr = start + idlen;
79
80 /*
81 * find end of fragment
82 */
83 {
84 __le32 *_map = (__le32 *)map;
85 u32 v = le32_to_cpu(_map[mapptr >> 5]) >> (mapptr & 31);
86 while (v == 0) {
87 mapptr = (mapptr & ~31) + 32;
88 if (mapptr >= mapsize)
89 goto error;
90 v = le32_to_cpu(_map[mapptr >> 5]);
91 }
92
93 mapptr += 1 + ffz(~v);
94 }
95
96 if (frag == frag_id)
97 goto found;
98 again:
99 start = mapptr;
100 } while (mapptr < mapsize);
101 return -1;
102
103 error:
104 printk(KERN_ERR "adfs: oversized fragment 0x%x at 0x%x-0x%x\n",
105 frag, start, mapptr);
106 return -1;
107
108 found:
109 {
110 int length = mapptr - start;
111 if (*offset >= length) {
112 *offset -= length;
113 goto again;
114 }
115 }
116 return start + *offset;
117 }
118
119 /*
120 * Scan the free space map, for this zone, calculating the total
121 * number of map bits in each free space fragment.
122 *
123 * Note: idmask is limited to 15 bits [3.2]
124 */
125 static unsigned int
126 scan_free_map(struct adfs_sb_info *asb, struct adfs_discmap *dm)
127 {
128 const unsigned int mapsize = dm->dm_endbit + 32;
129 const unsigned int idlen = asb->s_idlen;
130 const unsigned int frag_idlen = idlen <= 15 ? idlen : 15;
131 const u32 idmask = (1 << frag_idlen) - 1;
132 unsigned char *map = dm->dm_bh->b_data;
133 unsigned int start = 8, mapptr;
134 u32 frag;
135 unsigned long total = 0;
136
137 /*
138 * get fragment id
139 */
140 frag = GET_FRAG_ID(map, start, idmask);
141
142 /*
143 * If the freelink is null, then no free fragments
144 * exist in this zone.
145 */
146 if (frag == 0)
147 return 0;
148
149 do {
150 start += frag;
151
152 /*
153 * get fragment id
154 */
155 frag = GET_FRAG_ID(map, start, idmask);
156 mapptr = start + idlen;
157
158 /*
159 * find end of fragment
160 */
161 {
162 __le32 *_map = (__le32 *)map;
163 u32 v = le32_to_cpu(_map[mapptr >> 5]) >> (mapptr & 31);
164 while (v == 0) {
165 mapptr = (mapptr & ~31) + 32;
166 if (mapptr >= mapsize)
167 goto error;
168 v = le32_to_cpu(_map[mapptr >> 5]);
169 }
170
171 mapptr += 1 + ffz(~v);
172 }
173
174 total += mapptr - start;
175 } while (frag >= idlen + 1);
176
177 if (frag != 0)
178 printk(KERN_ERR "adfs: undersized free fragment\n");
179
180 return total;
181 error:
182 printk(KERN_ERR "adfs: oversized free fragment\n");
183 return 0;
184 }
185
186 static int scan_map(struct adfs_sb_info *asb, unsigned int zone,
187 const u32 frag_id, unsigned int mapoff)
188 {
189 const unsigned int idlen = asb->s_idlen;
190 struct adfs_discmap *dm, *dm_end;
191 int result;
192
193 dm = asb->s_map + zone;
194 zone = asb->s_map_size;
195 dm_end = asb->s_map + zone;
196
197 do {
198 result = lookup_zone(dm, idlen, frag_id, &mapoff);
199
200 if (result != -1)
201 goto found;
202
203 dm ++;
204 if (dm == dm_end)
205 dm = asb->s_map;
206 } while (--zone > 0);
207
208 return -1;
209 found:
210 result -= dm->dm_startbit;
211 result += dm->dm_startblk;
212
213 return result;
214 }
215
216 /*
217 * calculate the amount of free blocks in the map.
218 *
219 * n=1
220 * total_free = E(free_in_zone_n)
221 * nzones
222 */
223 unsigned int
224 adfs_map_free(struct super_block *sb)
225 {
226 struct adfs_sb_info *asb = ADFS_SB(sb);
227 struct adfs_discmap *dm;
228 unsigned int total = 0;
229 unsigned int zone;
230
231 dm = asb->s_map;
232 zone = asb->s_map_size;
233
234 do {
235 total += scan_free_map(asb, dm++);
236 } while (--zone > 0);
237
238 return signed_asl(total, asb->s_map2blk);
239 }
240
241 int adfs_map_lookup(struct super_block *sb, u32 frag_id, unsigned int offset)
242 {
243 struct adfs_sb_info *asb = ADFS_SB(sb);
244 unsigned int zone, mapoff;
245 int result;
246
247 /*
248 * map & root fragment is special - it starts in the center of the
249 * disk. The other fragments start at zone (frag / ids_per_zone)
250 */
251 if (frag_id == ADFS_ROOT_FRAG)
252 zone = asb->s_map_size >> 1;
253 else
254 zone = frag_id / asb->s_ids_per_zone;
255
256 if (zone >= asb->s_map_size)
257 goto bad_fragment;
258
259 /* Convert sector offset to map offset */
260 mapoff = signed_asl(offset, -asb->s_map2blk);
261
262 read_lock(&adfs_map_lock);
263 result = scan_map(asb, zone, frag_id, mapoff);
264 read_unlock(&adfs_map_lock);
265
266 if (result > 0) {
267 unsigned int secoff;
268
269 /* Calculate sector offset into map block */
270 secoff = offset - signed_asl(mapoff, asb->s_map2blk);
271 return secoff + signed_asl(result, asb->s_map2blk);
272 }
273
274 adfs_error(sb, "fragment 0x%04x at offset %d not found in map",
275 frag_id, offset);
276 return 0;
277
278 bad_fragment:
279 adfs_error(sb, "invalid fragment 0x%04x (zone = %d, max = %d)",
280 frag_id, zone, asb->s_map_size);
281 return 0;
282 }