summaryrefslogtreecommitdiff
path: root/fs/adfs/map.c
blob: 4d34338c61764c49e032b145ad72406d41e04598 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
// SPDX-License-Identifier: GPL-2.0-only
/*
 *  linux/fs/adfs/map.c
 *
 *  Copyright (C) 1997-2002 Russell King
 */
#include <linux/buffer_head.h>
#include <asm/unaligned.h>
#include "adfs.h"

/*
 * The ADFS map is basically a set of sectors.  Each sector is called a
 * zone which contains a bitstream made up of variable sized fragments.
 * Each bit refers to a set of bytes in the filesystem, defined by
 * log2bpmb.  This may be larger or smaller than the sector size, but
 * the overall size it describes will always be a round number of
 * sectors.  A fragment id is always idlen bits long.
 *
 *  < idlen > <       n        > <1>
 * +---------+-------//---------+---+
 * | frag id |  0000....000000  | 1 |
 * +---------+-------//---------+---+
 *
 * The physical disk space used by a fragment is taken from the start of
 * the fragment id up to and including the '1' bit - ie, idlen + n + 1
 * bits.
 *
 * A fragment id can be repeated multiple times in the whole map for
 * large or fragmented files.  The first map zone a fragment starts in
 * is given by fragment id / ids_per_zone - this allows objects to start
 * from any zone on the disk.
 *
 * Free space is described by a linked list of fragments.  Each free
 * fragment describes free space in the same way as the other fragments,
 * however, the frag id specifies an offset (in map bits) from the end
 * of this fragment to the start of the next free fragment.
 *
 * Objects stored on the disk are allocated object ids (we use these as
 * our inode numbers.)  Object ids contain a fragment id and an optional
 * offset.  This allows a directory fragment to contain small files
 * associated with that directory.
 */

/*
 * For the future...
 */
static DEFINE_RWLOCK(adfs_map_lock);

/*
 * This is fun.  We need to load up to 19 bits from the map at an
 * arbitrary bit alignment.  (We're limited to 19 bits by F+ version 2).
 */
#define GET_FRAG_ID(_map,_start,_idmask)				\
	({								\
		unsigned char *_m = _map + (_start >> 3);		\
		u32 _frag = get_unaligned_le32(_m);			\
		_frag >>= (_start & 7);					\
		_frag & _idmask;					\
	})

/*
 * return the map bit offset of the fragment frag_id in the zone dm.
 * Note that the loop is optimised for best asm code - look at the
 * output of:
 *  gcc -D__KERNEL__ -O2 -I../../include -o - -S map.c
 */
static int
lookup_zone(const struct adfs_discmap *dm, const unsigned int idlen,
	    const unsigned int frag_id, unsigned int *offset)
{
	const unsigned int mapsize = dm->dm_endbit;
	const u32 idmask = (1 << idlen) - 1;
	unsigned char *map = dm->dm_bh->b_data + 4;
	unsigned int start = dm->dm_startbit;
	unsigned int mapptr;
	u32 frag;

	do {
		frag = GET_FRAG_ID(map, start, idmask);
		mapptr = start + idlen;

		/*
		 * find end of fragment
		 */
		{
			__le32 *_map = (__le32 *)map;
			u32 v = le32_to_cpu(_map[mapptr >> 5]) >> (mapptr & 31);
			while (v == 0) {
				mapptr = (mapptr & ~31) + 32;
				if (mapptr >= mapsize)
					goto error;
				v = le32_to_cpu(_map[mapptr >> 5]);
			}

			mapptr += 1 + ffz(~v);
		}

		if (frag == frag_id)
			goto found;
again:
		start = mapptr;
	} while (mapptr < mapsize);
	return -1;

error:
	printk(KERN_ERR "adfs: oversized fragment 0x%x at 0x%x-0x%x\n",
		frag, start, mapptr);
	return -1;

found:
	{
		int length = mapptr - start;
		if (*offset >= length) {
			*offset -= length;
			goto again;
		}
	}
	return start + *offset;
}

/*
 * Scan the free space map, for this zone, calculating the total
 * number of map bits in each free space fragment.
 *
 * Note: idmask is limited to 15 bits [3.2]
 */
static unsigned int
scan_free_map(struct adfs_sb_info *asb, struct adfs_discmap *dm)
{
	const unsigned int mapsize = dm->dm_endbit + 32;
	const unsigned int idlen  = asb->s_idlen;
	const unsigned int frag_idlen = idlen <= 15 ? idlen : 15;
	const u32 idmask = (1 << frag_idlen) - 1;
	unsigned char *map = dm->dm_bh->b_data;
	unsigned int start = 8, mapptr;
	u32 frag;
	unsigned long total = 0;

	/*
	 * get fragment id
	 */
	frag = GET_FRAG_ID(map, start, idmask);

	/*
	 * If the freelink is null, then no free fragments
	 * exist in this zone.
	 */
	if (frag == 0)
		return 0;

	do {
		start += frag;

		/*
		 * get fragment id
		 */
		frag = GET_FRAG_ID(map, start, idmask);
		mapptr = start + idlen;

		/*
		 * find end of fragment
		 */
		{
			__le32 *_map = (__le32 *)map;
			u32 v = le32_to_cpu(_map[mapptr >> 5]) >> (mapptr & 31);
			while (v == 0) {
				mapptr = (mapptr & ~31) + 32;
				if (mapptr >= mapsize)
					goto error;
				v = le32_to_cpu(_map[mapptr >> 5]);
			}

			mapptr += 1 + ffz(~v);
		}

		total += mapptr - start;
	} while (frag >= idlen + 1);

	if (frag != 0)
		printk(KERN_ERR "adfs: undersized free fragment\n");

	return total;
error:
	printk(KERN_ERR "adfs: oversized free fragment\n");
	return 0;
}

static int
scan_map(struct adfs_sb_info *asb, unsigned int zone,
	 const unsigned int frag_id, unsigned int mapoff)
{
	const unsigned int idlen = asb->s_idlen;
	struct adfs_discmap *dm, *dm_end;
	int result;

	dm	= asb->s_map + zone;
	zone	= asb->s_map_size;
	dm_end	= asb->s_map + zone;

	do {
		result = lookup_zone(dm, idlen, frag_id, &mapoff);

		if (result != -1)
			goto found;

		dm ++;
		if (dm == dm_end)
			dm = asb->s_map;
	} while (--zone > 0);

	return -1;
found:
	result -= dm->dm_startbit;
	result += dm->dm_startblk;

	return result;
}

/*
 * calculate the amount of free blocks in the map.
 *
 *              n=1
 *  total_free = E(free_in_zone_n)
 *              nzones
 */
unsigned int
adfs_map_free(struct super_block *sb)
{
	struct adfs_sb_info *asb = ADFS_SB(sb);
	struct adfs_discmap *dm;
	unsigned int total = 0;
	unsigned int zone;

	dm   = asb->s_map;
	zone = asb->s_map_size;

	do {
		total += scan_free_map(asb, dm++);
	} while (--zone > 0);

	return signed_asl(total, asb->s_map2blk);
}

int
adfs_map_lookup(struct super_block *sb, unsigned int frag_id,
		unsigned int offset)
{
	struct adfs_sb_info *asb = ADFS_SB(sb);
	unsigned int zone, mapoff;
	int result;

	/*
	 * map & root fragment is special - it starts in the center of the
	 * disk.  The other fragments start at zone (frag / ids_per_zone)
	 */
	if (frag_id == ADFS_ROOT_FRAG)
		zone = asb->s_map_size >> 1;
	else
		zone = frag_id / asb->s_ids_per_zone;

	if (zone >= asb->s_map_size)
		goto bad_fragment;

	/* Convert sector offset to map offset */
	mapoff = signed_asl(offset, -asb->s_map2blk);

	read_lock(&adfs_map_lock);
	result = scan_map(asb, zone, frag_id, mapoff);
	read_unlock(&adfs_map_lock);

	if (result > 0) {
		unsigned int secoff;

		/* Calculate sector offset into map block */
		secoff = offset - signed_asl(mapoff, asb->s_map2blk);
		return secoff + signed_asl(result, asb->s_map2blk);
	}

	adfs_error(sb, "fragment 0x%04x at offset %d not found in map",
		   frag_id, offset);
	return 0;

bad_fragment:
	adfs_error(sb, "invalid fragment 0x%04x (zone = %d, max = %d)",
		   frag_id, zone, asb->s_map_size);
	return 0;
}