fs/adfs/map.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  *  linux/fs/adfs/map.c
   4  *
   5  *  Copyright (C) 1997-2002 Russell King
   6  */
   7 #include <asm/unaligned.h>
   8 #include "adfs.h"
   9
  10 /*
  11  * The ADFS map is basically a set of sectors.  Each sector is called a
  12  * zone which contains a bitstream made up of variable sized fragments.
  13  * Each bit refers to a set of bytes in the filesystem, defined by
  14  * log2bpmb.  This may be larger or smaller than the sector size, but
  15  * the overall size it describes will always be a round number of
  16  * sectors.  A fragment id is always idlen bits long.
  17  *
  18  *  < idlen > <       n        > <1>
  19  * +---------+-------//---------+---+
  20  * | frag id |  0000....000000  | 1 |
  21  * +---------+-------//---------+---+
  22  *
  23  * The physical disk space used by a fragment is taken from the start of
  24  * the fragment id up to and including the '1' bit - ie, idlen + n + 1
  25  * bits.
  26  *
  27  * A fragment id can be repeated multiple times in the whole map for
  28  * large or fragmented files.  The first map zone a fragment starts in
  29  * is given by fragment id / ids_per_zone - this allows objects to start
  30  * from any zone on the disk.
  31  *
  32  * Free space is described by a linked list of fragments.  Each free
  33  * fragment describes free space in the same way as the other fragments,
  34  * however, the frag id specifies an offset (in map bits) from the end
  35  * of this fragment to the start of the next free fragment.
  36  *
  37  * Objects stored on the disk are allocated object ids (we use these as
  38  * our inode numbers.)  Object ids contain a fragment id and an optional
  39  * offset.  This allows a directory fragment to contain small files
  40  * associated with that directory.
  41  */
  42
  43 /*
  44  * For the future...
  45  */
  46 static DEFINE_RWLOCK(adfs_map_lock);
  47
  48 /*
  49  * This is fun.  We need to load up to 19 bits from the map at an
  50  * arbitrary bit alignment.  (We're limited to 19 bits by F+ version 2).
  51  */
  52 #define GET_FRAG_ID(_map,_start,_idmask)                                \
  53         ({                                                              \
  54                 unsigned char *_m = _map + (_start >> 3);               \
  55                 u32 _frag = get_unaligned_le32(_m);                     \
  56                 _frag >>= (_start & 7);                                 \
  57                 _frag & _idmask;                                        \
  58         })
  59
  60 /*
  61  * return the map bit offset of the fragment frag_id in the zone dm.
  62  * Note that the loop is optimised for best asm code - look at the
  63  * output of:
  64  *  gcc -D__KERNEL__ -O2 -I../../include -o - -S map.c
  65  */
  66 static int lookup_zone(const struct adfs_discmap *dm, const unsigned int idlen,
  67                        const u32 frag_id, unsigned int *offset)
  68 {
  69         const unsigned int mapsize = dm->dm_endbit;
  70         const u32 idmask = (1 << idlen) - 1;
  71         unsigned char *map = dm->dm_bh->b_data + 4;
  72         unsigned int start = dm->dm_startbit;
  73         unsigned int mapptr;
  74         u32 frag;
  75
  76         do {
  77                 frag = GET_FRAG_ID(map, start, idmask);
  78                 mapptr = start + idlen;
  79
  80                 /*
  81                  * find end of fragment
  82                  */
  83                 {
  84                         __le32 *_map = (__le32 *)map;
  85                         u32 v = le32_to_cpu(_map[mapptr >> 5]) >> (mapptr & 31);
  86                         while (v == 0) {
  87                                 mapptr = (mapptr & ~31) + 32;
  88                                 if (mapptr >= mapsize)
  89                                         goto error;
  90                                 v = le32_to_cpu(_map[mapptr >> 5]);
  91                         }
  92
  93                         mapptr += 1 + ffz(~v);
  94                 }
  95
  96                 if (frag == frag_id)
  97                         goto found;
  98 again:
  99                 start = mapptr;
 100         } while (mapptr < mapsize);
 101         return -1;
 102
 103 error:
 104         printk(KERN_ERR "adfs: oversized fragment 0x%x at 0x%x-0x%x\n",
 105                 frag, start, mapptr);
 106         return -1;
 107
 108 found:
 109         {
 110                 int length = mapptr - start;
 111                 if (*offset >= length) {
 112                         *offset -= length;
 113                         goto again;
 114                 }
 115         }
 116         return start + *offset;
 117 }
 118
 119 /*
 120  * Scan the free space map, for this zone, calculating the total
 121  * number of map bits in each free space fragment.
 122  *
 123  * Note: idmask is limited to 15 bits [3.2]
 124  */
 125 static unsigned int
 126 scan_free_map(struct adfs_sb_info *asb, struct adfs_discmap *dm)
 127 {
 128         const unsigned int mapsize = dm->dm_endbit + 32;
 129         const unsigned int idlen  = asb->s_idlen;
 130         const unsigned int frag_idlen = idlen <= 15 ? idlen : 15;
 131         const u32 idmask = (1 << frag_idlen) - 1;
 132         unsigned char *map = dm->dm_bh->b_data;
 133         unsigned int start = 8, mapptr;
 134         u32 frag;
 135         unsigned long total = 0;
 136
 137         /*
 138          * get fragment id
 139          */
 140         frag = GET_FRAG_ID(map, start, idmask);
 141
 142         /*
 143          * If the freelink is null, then no free fragments
 144          * exist in this zone.
 145          */
 146         if (frag == 0)
 147                 return 0;
 148
 149         do {
 150                 start += frag;
 151
 152                 /*
 153                  * get fragment id
 154                  */
 155                 frag = GET_FRAG_ID(map, start, idmask);
 156                 mapptr = start + idlen;
 157
 158                 /*
 159                  * find end of fragment
 160                  */
 161                 {
 162                         __le32 *_map = (__le32 *)map;
 163                         u32 v = le32_to_cpu(_map[mapptr >> 5]) >> (mapptr & 31);
 164                         while (v == 0) {
 165                                 mapptr = (mapptr & ~31) + 32;
 166                                 if (mapptr >= mapsize)
 167                                         goto error;
 168                                 v = le32_to_cpu(_map[mapptr >> 5]);
 169                         }
 170
 171                         mapptr += 1 + ffz(~v);
 172                 }
 173
 174                 total += mapptr - start;
 175         } while (frag >= idlen + 1);
 176
 177         if (frag != 0)
 178                 printk(KERN_ERR "adfs: undersized free fragment\n");
 179
 180         return total;
 181 error:
 182         printk(KERN_ERR "adfs: oversized free fragment\n");
 183         return 0;
 184 }
 185
 186 static int scan_map(struct adfs_sb_info *asb, unsigned int zone,
 187                     const u32 frag_id, unsigned int mapoff)
 188 {
 189         const unsigned int idlen = asb->s_idlen;
 190         struct adfs_discmap *dm, *dm_end;
 191         int result;
 192
 193         dm      = asb->s_map + zone;
 194         zone    = asb->s_map_size;
 195         dm_end  = asb->s_map + zone;
 196
 197         do {
 198                 result = lookup_zone(dm, idlen, frag_id, &mapoff);
 199
 200                 if (result != -1)
 201                         goto found;
 202
 203                 dm ++;
 204                 if (dm == dm_end)
 205                         dm = asb->s_map;
 206         } while (--zone > 0);
 207
 208         return -1;
 209 found:
 210         result -= dm->dm_startbit;
 211         result += dm->dm_startblk;
 212
 213         return result;
 214 }
 215
 216 /*
 217  * calculate the amount of free blocks in the map.
 218  *
 219  *              n=1
 220  *  total_free = E(free_in_zone_n)
 221  *              nzones
 222  */
 223 unsigned int
 224 adfs_map_free(struct super_block *sb)
 225 {
 226         struct adfs_sb_info *asb = ADFS_SB(sb);
 227         struct adfs_discmap *dm;
 228         unsigned int total = 0;
 229         unsigned int zone;
 230
 231         dm   = asb->s_map;
 232         zone = asb->s_map_size;
 233
 234         do {
 235                 total += scan_free_map(asb, dm++);
 236         } while (--zone > 0);
 237
 238         return signed_asl(total, asb->s_map2blk);
 239 }
 240
 241 int adfs_map_lookup(struct super_block *sb, u32 frag_id, unsigned int offset)
 242 {
 243         struct adfs_sb_info *asb = ADFS_SB(sb);
 244         unsigned int zone, mapoff;
 245         int result;
 246
 247         /*
 248          * map & root fragment is special - it starts in the center of the
 249          * disk.  The other fragments start at zone (frag / ids_per_zone)
 250          */
 251         if (frag_id == ADFS_ROOT_FRAG)
 252                 zone = asb->s_map_size >> 1;
 253         else
 254                 zone = frag_id / asb->s_ids_per_zone;
 255
 256         if (zone >= asb->s_map_size)
 257                 goto bad_fragment;
 258
 259         /* Convert sector offset to map offset */
 260         mapoff = signed_asl(offset, -asb->s_map2blk);
 261
 262         read_lock(&adfs_map_lock);
 263         result = scan_map(asb, zone, frag_id, mapoff);
 264         read_unlock(&adfs_map_lock);
 265
 266         if (result > 0) {
 267                 unsigned int secoff;
 268
 269                 /* Calculate sector offset into map block */
 270                 secoff = offset - signed_asl(mapoff, asb->s_map2blk);
 271                 return secoff + signed_asl(result, asb->s_map2blk);
 272         }
 273
 274         adfs_error(sb, "fragment 0x%04x at offset %d not found in map",
 275                    frag_id, offset);
 276         return 0;
 277
 278 bad_fragment:
 279         adfs_error(sb, "invalid fragment 0x%04x (zone = %d, max = %d)",
 280                    frag_id, zone, asb->s_map_size);
 281         return 0;
 282 }