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Linux/fs/adfs/map.c

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  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  */
 50 static 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  * arbitrary 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  */
 70 static int
 71 lookup_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;
103 again:
104                 start = mapptr;
105         } while (mapptr < mapsize);
106         return -1;
107 
108 error:
109         printk(KERN_ERR "adfs: oversized fragment 0x%x at 0x%x-0x%x\n",
110                 frag, start, mapptr);
111         return -1;
112 
113 found:
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  */
130 static unsigned int
131 scan_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;
186 error:
187         printk(KERN_ERR "adfs: oversized free fragment\n");
188         return 0;
189 }
190 
191 static int
192 scan_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;
215 found:
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  */
229 unsigned int
230 adfs_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 
247 int
248 adfs_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 
286 bad_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 

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