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/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 }