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/buffer_head.h>
11#include <asm/unaligned.h>
12#include "adfs.h"
13
14/*
15 * The ADFS map is basically a set of sectors.  Each sector is called a
16 * zone which contains a bitstream made up of variable sized fragments.
17 * Each bit refers to a set of bytes in the filesystem, defined by
18 * log2bpmb.  This may be larger or smaller than the sector size, but
19 * the overall size it describes will always be a round number of
20 * sectors.  A fragment id is always idlen bits long.
21 *
22 *  < idlen > <       n        > <1>
23 * +---------+-------//---------+---+
24 * | frag id |  0000....000000  | 1 |
25 * +---------+-------//---------+---+
26 *
27 * The physical disk space used by a fragment is taken from the start of
28 * the fragment id up to and including the '1' bit - ie, idlen + n + 1
29 * bits.
30 *
31 * A fragment id can be repeated multiple times in the whole map for
32 * large or fragmented files.  The first map zone a fragment starts in
33 * is given by fragment id / ids_per_zone - this allows objects to start
34 * from any zone on the disk.
35 *
36 * Free space is described by a linked list of fragments.  Each free
37 * fragment describes free space in the same way as the other fragments,
38 * however, the frag id specifies an offset (in map bits) from the end
39 * of this fragment to the start of the next free fragment.
40 *
41 * Objects stored on the disk are allocated object ids (we use these as
42 * our inode numbers.)  Object ids contain a fragment id and an optional
43 * offset.  This allows a directory fragment to contain small files
44 * associated with that directory.
45 */
46
47/*
48 * For the future...
49 */
50static DEFINE_RWLOCK(adfs_map_lock);
51
52/*
53 * This is fun.  We need to load up to 19 bits from the map at an
54 * arbitary bit alignment.  (We're limited to 19 bits by F+ version 2).
55 */
56#define GET_FRAG_ID(_map,_start,_idmask)				\
57	({								\
58		unsigned char *_m = _map + (_start >> 3);		\
59		u32 _frag = get_unaligned_le32(_m);			\
60		_frag >>= (_start & 7);					\
61		_frag & _idmask;					\
62	})
63
64/*
65 * return the map bit offset of the fragment frag_id in the zone dm.
66 * Note that the loop is optimised for best asm code - look at the
67 * output of:
68 *  gcc -D__KERNEL__ -O2 -I../../include -o - -S map.c
69 */
70static int
71lookup_zone(const struct adfs_discmap *dm, const unsigned int idlen,
72	    const unsigned int frag_id, unsigned int *offset)
73{
74	const unsigned int mapsize = dm->dm_endbit;
75	const u32 idmask = (1 << idlen) - 1;
76	unsigned char *map = dm->dm_bh->b_data + 4;
77	unsigned int start = dm->dm_startbit;
78	unsigned int mapptr;
79	u32 frag;
80
81	do {
82		frag = GET_FRAG_ID(map, start, idmask);
83		mapptr = start + idlen;
84
85		/*
86		 * find end of fragment
87		 */
88		{
89			__le32 *_map = (__le32 *)map;
90			u32 v = le32_to_cpu(_map[mapptr >> 5]) >> (mapptr & 31);
91			while (v == 0) {
92				mapptr = (mapptr & ~31) + 32;
93				if (mapptr >= mapsize)
94					goto error;
95				v = le32_to_cpu(_map[mapptr >> 5]);
96			}
97
98			mapptr += 1 + ffz(~v);
99		}
100
101		if (frag == frag_id)
102			goto found;
103again:
104		start = mapptr;
105	} while (mapptr < mapsize);
106	return -1;
107
108error:
109	printk(KERN_ERR "adfs: oversized fragment 0x%x at 0x%x-0x%x\n",
110		frag, start, mapptr);
111	return -1;
112
113found:
114	{
115		int length = mapptr - start;
116		if (*offset >= length) {
117			*offset -= length;
118			goto again;
119		}
120	}
121	return start + *offset;
122}
123
124/*
125 * Scan the free space map, for this zone, calculating the total
126 * number of map bits in each free space fragment.
127 *
128 * Note: idmask is limited to 15 bits [3.2]
129 */
130static unsigned int
131scan_free_map(struct adfs_sb_info *asb, struct adfs_discmap *dm)
132{
133	const unsigned int mapsize = dm->dm_endbit + 32;
134	const unsigned int idlen  = asb->s_idlen;
135	const unsigned int frag_idlen = idlen <= 15 ? idlen : 15;
136	const u32 idmask = (1 << frag_idlen) - 1;
137	unsigned char *map = dm->dm_bh->b_data;
138	unsigned int start = 8, mapptr;
139	u32 frag;
140	unsigned long total = 0;
141
142	/*
143	 * get fragment id
144	 */
145	frag = GET_FRAG_ID(map, start, idmask);
146
147	/*
148	 * If the freelink is null, then no free fragments
149	 * exist in this zone.
150	 */
151	if (frag == 0)
152		return 0;
153
154	do {
155		start += frag;
156
157		/*
158		 * get fragment id
159		 */
160		frag = GET_FRAG_ID(map, start, idmask);
161		mapptr = start + idlen;
162
163		/*
164		 * find end of fragment
165		 */
166		{
167			__le32 *_map = (__le32 *)map;
168			u32 v = le32_to_cpu(_map[mapptr >> 5]) >> (mapptr & 31);
169			while (v == 0) {
170				mapptr = (mapptr & ~31) + 32;
171				if (mapptr >= mapsize)
172					goto error;
173				v = le32_to_cpu(_map[mapptr >> 5]);
174			}
175
176			mapptr += 1 + ffz(~v);
177		}
178
179		total += mapptr - start;
180	} while (frag >= idlen + 1);
181
182	if (frag != 0)
183		printk(KERN_ERR "adfs: undersized free fragment\n");
184
185	return total;
186error:
187	printk(KERN_ERR "adfs: oversized free fragment\n");
188	return 0;
189}
190
191static int
192scan_map(struct adfs_sb_info *asb, unsigned int zone,
193	 const unsigned int frag_id, unsigned int mapoff)
194{
195	const unsigned int idlen = asb->s_idlen;
196	struct adfs_discmap *dm, *dm_end;
197	int result;
198
199	dm	= asb->s_map + zone;
200	zone	= asb->s_map_size;
201	dm_end	= asb->s_map + zone;
202
203	do {
204		result = lookup_zone(dm, idlen, frag_id, &mapoff);
205
206		if (result != -1)
207			goto found;
208
209		dm ++;
210		if (dm == dm_end)
211			dm = asb->s_map;
212	} while (--zone > 0);
213
214	return -1;
215found:
216	result -= dm->dm_startbit;
217	result += dm->dm_startblk;
218
219	return result;
220}
221
222/*
223 * calculate the amount of free blocks in the map.
224 *
225 *              n=1
226 *  total_free = E(free_in_zone_n)
227 *              nzones
228 */
229unsigned int
230adfs_map_free(struct super_block *sb)
231{
232	struct adfs_sb_info *asb = ADFS_SB(sb);
233	struct adfs_discmap *dm;
234	unsigned int total = 0;
235	unsigned int zone;
236
237	dm   = asb->s_map;
238	zone = asb->s_map_size;
239
240	do {
241		total += scan_free_map(asb, dm++);
242	} while (--zone > 0);
243
244	return signed_asl(total, asb->s_map2blk);
245}
246
247int
248adfs_map_lookup(struct super_block *sb, unsigned int frag_id,
249		unsigned int offset)
250{
251	struct adfs_sb_info *asb = ADFS_SB(sb);
252	unsigned int zone, mapoff;
253	int result;
254
255	/*
256	 * map & root fragment is special - it starts in the center of the
257	 * disk.  The other fragments start at zone (frag / ids_per_zone)
258	 */
259	if (frag_id == ADFS_ROOT_FRAG)
260		zone = asb->s_map_size >> 1;
261	else
262		zone = frag_id / asb->s_ids_per_zone;
263
264	if (zone >= asb->s_map_size)
265		goto bad_fragment;
266
267	/* Convert sector offset to map offset */
268	mapoff = signed_asl(offset, -asb->s_map2blk);
269
270	read_lock(&adfs_map_lock);
271	result = scan_map(asb, zone, frag_id, mapoff);
272	read_unlock(&adfs_map_lock);
273
274	if (result > 0) {
275		unsigned int secoff;
276
277		/* Calculate sector offset into map block */
278		secoff = offset - signed_asl(mapoff, asb->s_map2blk);
279		return secoff + signed_asl(result, asb->s_map2blk);
280	}
281
282	adfs_error(sb, "fragment 0x%04x at offset %d not found in map",
283		   frag_id, offset);
284	return 0;
285
286bad_fragment:
287	adfs_error(sb, "invalid fragment 0x%04x (zone = %d, max = %d)",
288		   frag_id, zone, asb->s_map_size);
289	return 0;
290}
291