fs/adfs/map.c

   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  */
  56 static rwlock_t adfs_map_lock = RW_LOCK_UNLOCKED;
  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  */
  76 static int
  77 lookup_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;
 109 again:
 110                 start = mapptr;
 111         } while (mapptr < mapsize);
 112         return -1;
 113
 114 error:
 115         printk(KERN_ERR "adfs: oversized fragment 0x%x at 0x%x-0x%x\n",
 116                 frag, start, mapptr);
 117         return -1;
 118
 119 found:
 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  */
 136 static unsigned int
 137 scan_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;
 192 error:
 193         printk(KERN_ERR "adfs: oversized free fragment\n");
 194         return 0;
 195 }
 196
 197 static int
 198 scan_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;
 221 found:
 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  */
 235 unsigned int
 236 adfs_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
 253 int
 254 adfs_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
 292 bad_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 }