1/*
2 *  linux/fs/adfs/map.c
3 *
4 *  Copyright (C) 1997-2002 Russell King
5 *
6 * This program is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License version 2 as
8 * published by the Free Software Foundation.
9 */
10#include <linux/errno.h>
11#include <linux/fs.h>
12#include <linux/adfs_fs.h>
13#include <linux/spinlock.h>
14#include <linux/buffer_head.h>
15
16#include <asm/unaligned.h>
17
18#include "adfs.h"
19
20/*
21 * The ADFS map is basically a set of sectors.  Each sector is called a
22 * zone which contains a bitstream made up of variable sized fragments.
23 * Each bit refers to a set of bytes in the filesystem, defined by
24 * log2bpmb.  This may be larger or smaller than the sector size, but
25 * the overall size it describes will always be a round number of
26 * sectors.  A fragment id is always idlen bits long.
27 *
28 *  < idlen > <       n        > <1>
29 * +---------+-------//---------+---+
30 * | frag id |  0000....000000  | 1 |
31 * +---------+-------//---------+---+
32 *
33 * The physical disk space used by a fragment is taken from the start of
34 * the fragment id up to and including the '1' bit - ie, idlen + n + 1
35 * bits.
36 *
37 * A fragment id can be repeated multiple times in the whole map for
38 * large or fragmented files.  The first map zone a fragment starts in
39 * is given by fragment id / ids_per_zone - this allows objects to start
40 * from any zone on the disk.
41 *
42 * Free space is described by a linked list of fragments.  Each free
43 * fragment describes free space in the same way as the other fragments,
44 * however, the frag id specifies an offset (in map bits) from the end
45 * of this fragment to the start of the next free fragment.
46 *
47 * Objects stored on the disk are allocated object ids (we use these as
48 * our inode numbers.)  Object ids contain a fragment id and an optional
49 * offset.  This allows a directory fragment to contain small files
50 * associated with that directory.
51 */
52
53/*
54 * For the future...
55 */
56static DEFINE_RWLOCK(adfs_map_lock);
57
58/*
59 * This is fun.  We need to load up to 19 bits from the map at an
60 * arbitary bit alignment.  (We're limited to 19 bits by F+ version 2).
61 */
62#define GET_FRAG_ID(_map,_start,_idmask)				\
63	({								\
64		unsigned char *_m = _map + (_start >> 3);		\
65		u32 _frag = get_unaligned((u32 *)_m);			\
66		_frag >>= (_start & 7);					\
67		_frag & _idmask;					\
68	})
69
70/*
71 * return the map bit offset of the fragment frag_id in the zone dm.
72 * Note that the loop is optimised for best asm code - look at the
73 * output of:
74 *  gcc -D__KERNEL__ -O2 -I../../include -o - -S map.c
75 */
76static int
77lookup_zone(const struct adfs_discmap *dm, const unsigned int idlen,
78	    const unsigned int frag_id, unsigned int *offset)
79{
80	const unsigned int mapsize = dm->dm_endbit;
81	const u32 idmask = (1 << idlen) - 1;
82	unsigned char *map = dm->dm_bh->b_data + 4;
83	unsigned int start = dm->dm_startbit;
84	unsigned int mapptr;
85	u32 frag;
86
87	do {
88		frag = GET_FRAG_ID(map, start, idmask);
89		mapptr = start + idlen;
90
91		/*
92		 * find end of fragment
93		 */
94		{
95			__le32 *_map = (__le32 *)map;
96			u32 v = le32_to_cpu(_map[mapptr >> 5]) >> (mapptr & 31);
97			while (v == 0) {
98				mapptr = (mapptr & ~31) + 32;
99				if (mapptr >= mapsize)
100					goto error;
101				v = le32_to_cpu(_map[mapptr >> 5]);
102			}
103
104			mapptr += 1 + ffz(~v);
105		}
106
107		if (frag == frag_id)
108			goto found;
109again:
110		start = mapptr;
111	} while (mapptr < mapsize);
112	return -1;
113
114error:
115	printk(KERN_ERR "adfs: oversized fragment 0x%x at 0x%x-0x%x\n",
116		frag, start, mapptr);
117	return -1;
118
119found:
120	{
121		int length = mapptr - start;
122		if (*offset >= length) {
123			*offset -= length;
124			goto again;
125		}
126	}
127	return start + *offset;
128}
129
130/*
131 * Scan the free space map, for this zone, calculating the total
132 * number of map bits in each free space fragment.
133 *
134 * Note: idmask is limited to 15 bits [3.2]
135 */
136static unsigned int
137scan_free_map(struct adfs_sb_info *asb, struct adfs_discmap *dm)
138{
139	const unsigned int mapsize = dm->dm_endbit + 32;
140	const unsigned int idlen  = asb->s_idlen;
141	const unsigned int frag_idlen = idlen <= 15 ? idlen : 15;
142	const u32 idmask = (1 << frag_idlen) - 1;
143	unsigned char *map = dm->dm_bh->b_data;
144	unsigned int start = 8, mapptr;
145	u32 frag;
146	unsigned long total = 0;
147
148	/*
149	 * get fragment id
150	 */
151	frag = GET_FRAG_ID(map, start, idmask);
152
153	/*
154	 * If the freelink is null, then no free fragments
155	 * exist in this zone.
156	 */
157	if (frag == 0)
158		return 0;
159
160	do {
161		start += frag;
162
163		/*
164		 * get fragment id
165		 */
166		frag = GET_FRAG_ID(map, start, idmask);
167		mapptr = start + idlen;
168
169		/*
170		 * find end of fragment
171		 */
172		{
173			__le32 *_map = (__le32 *)map;
174			u32 v = le32_to_cpu(_map[mapptr >> 5]) >> (mapptr & 31);
175			while (v == 0) {
176				mapptr = (mapptr & ~31) + 32;
177				if (mapptr >= mapsize)
178					goto error;
179				v = le32_to_cpu(_map[mapptr >> 5]);
180			}
181
182			mapptr += 1 + ffz(~v);
183		}
184
185		total += mapptr - start;
186	} while (frag >= idlen + 1);
187
188	if (frag != 0)
189		printk(KERN_ERR "adfs: undersized free fragment\n");
190
191	return total;
192error:
193	printk(KERN_ERR "adfs: oversized free fragment\n");
194	return 0;
195}
196
197static int
198scan_map(struct adfs_sb_info *asb, unsigned int zone,
199	 const unsigned int frag_id, unsigned int mapoff)
200{
201	const unsigned int idlen = asb->s_idlen;
202	struct adfs_discmap *dm, *dm_end;
203	int result;
204
205	dm	= asb->s_map + zone;
206	zone	= asb->s_map_size;
207	dm_end	= asb->s_map + zone;
208
209	do {
210		result = lookup_zone(dm, idlen, frag_id, &mapoff);
211
212		if (result != -1)
213			goto found;
214
215		dm ++;
216		if (dm == dm_end)
217			dm = asb->s_map;
218	} while (--zone > 0);
219
220	return -1;
221found:
222	result -= dm->dm_startbit;
223	result += dm->dm_startblk;
224
225	return result;
226}
227
228/*
229 * calculate the amount of free blocks in the map.
230 *
231 *              n=1
232 *  total_free = E(free_in_zone_n)
233 *              nzones
234 */
235unsigned int
236adfs_map_free(struct super_block *sb)
237{
238	struct adfs_sb_info *asb = ADFS_SB(sb);
239	struct adfs_discmap *dm;
240	unsigned int total = 0;
241	unsigned int zone;
242
243	dm   = asb->s_map;
244	zone = asb->s_map_size;
245
246	do {
247		total += scan_free_map(asb, dm++);
248	} while (--zone > 0);
249
250	return signed_asl(total, asb->s_map2blk);
251}
252
253int
254adfs_map_lookup(struct super_block *sb, unsigned int frag_id,
255		unsigned int offset)
256{
257	struct adfs_sb_info *asb = ADFS_SB(sb);
258	unsigned int zone, mapoff;
259	int result;
260
261	/*
262	 * map & root fragment is special - it starts in the center of the
263	 * disk.  The other fragments start at zone (frag / ids_per_zone)
264	 */
265	if (frag_id == ADFS_ROOT_FRAG)
266		zone = asb->s_map_size >> 1;
267	else
268		zone = frag_id / asb->s_ids_per_zone;
269
270	if (zone >= asb->s_map_size)
271		goto bad_fragment;
272
273	/* Convert sector offset to map offset */
274	mapoff = signed_asl(offset, -asb->s_map2blk);
275
276	read_lock(&adfs_map_lock);
277	result = scan_map(asb, zone, frag_id, mapoff);
278	read_unlock(&adfs_map_lock);
279
280	if (result > 0) {
281		unsigned int secoff;
282
283		/* Calculate sector offset into map block */
284		secoff = offset - signed_asl(mapoff, asb->s_map2blk);
285		return secoff + signed_asl(result, asb->s_map2blk);
286	}
287
288	adfs_error(sb, "fragment 0x%04x at offset %d not found in map",
289		   frag_id, offset);
290	return 0;
291
292bad_fragment:
293	adfs_error(sb, "invalid fragment 0x%04x (zone = %d, max = %d)",
294		   frag_id, zone, asb->s_map_size);
295	return 0;
296}
297