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 */
  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 * 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 */
  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
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