fs/adfs/map.c

0001 // SPDX-License-Identifier: GPL-2.0-only
0002 /*
0003  *  linux/fs/adfs/map.c
0004  *
0005  *  Copyright (C) 1997-2002 Russell King
0006  */
0007 #include <linux/slab.h>
0008 #include <linux/statfs.h>
0009 #include <asm/unaligned.h>
0010 #include "adfs.h"
0011
0012 /*
0013  * The ADFS map is basically a set of sectors.  Each sector is called a
0014  * zone which contains a bitstream made up of variable sized fragments.
0015  * Each bit refers to a set of bytes in the filesystem, defined by
0016  * log2bpmb.  This may be larger or smaller than the sector size, but
0017  * the overall size it describes will always be a round number of
0018  * sectors.  A fragment id is always idlen bits long.
0019  *
0020  *  < idlen > <       n        > <1>
0021  * +---------+-------//---------+---+
0022  * | frag id |  0000....000000  | 1 |
0023  * +---------+-------//---------+---+
0024  *
0025  * The physical disk space used by a fragment is taken from the start of
0026  * the fragment id up to and including the '1' bit - ie, idlen + n + 1
0027  * bits.
0028  *
0029  * A fragment id can be repeated multiple times in the whole map for
0030  * large or fragmented files.  The first map zone a fragment starts in
0031  * is given by fragment id / ids_per_zone - this allows objects to start
0032  * from any zone on the disk.
0033  *
0034  * Free space is described by a linked list of fragments.  Each free
0035  * fragment describes free space in the same way as the other fragments,
0036  * however, the frag id specifies an offset (in map bits) from the end
0037  * of this fragment to the start of the next free fragment.
0038  *
0039  * Objects stored on the disk are allocated object ids (we use these as
0040  * our inode numbers.)  Object ids contain a fragment id and an optional
0041  * offset.  This allows a directory fragment to contain small files
0042  * associated with that directory.
0043  */
0044
0045 /*
0046  * For the future...
0047  */
0048 static DEFINE_RWLOCK(adfs_map_lock);
0049
0050 /*
0051  * This is fun.  We need to load up to 19 bits from the map at an
0052  * arbitrary bit alignment.  (We're limited to 19 bits by F+ version 2).
0053  */
0054 #define GET_FRAG_ID(_map,_start,_idmask)                \
0055     ({                              \
0056         unsigned char *_m = _map + (_start >> 3);       \
0057         u32 _frag = get_unaligned_le32(_m);         \
0058         _frag >>= (_start & 7);                 \
0059         _frag & _idmask;                    \
0060     })
0061
0062 /*
0063  * return the map bit offset of the fragment frag_id in the zone dm.
0064  * Note that the loop is optimised for best asm code - look at the
0065  * output of:
0066  *  gcc -D__KERNEL__ -O2 -I../../include -o - -S map.c
0067  */
0068 static int lookup_zone(const struct adfs_discmap *dm, const unsigned int idlen,
0069                const u32 frag_id, unsigned int *offset)
0070 {
0071     const unsigned int endbit = dm->dm_endbit;
0072     const u32 idmask = (1 << idlen) - 1;
0073     unsigned char *map = dm->dm_bh->b_data;
0074     unsigned int start = dm->dm_startbit;
0075     unsigned int freelink, fragend;
0076     u32 frag;
0077
0078     frag = GET_FRAG_ID(map, 8, idmask & 0x7fff);
0079     freelink = frag ? 8 + frag : 0;
0080
0081     do {
0082         frag = GET_FRAG_ID(map, start, idmask);
0083
0084         fragend = find_next_bit_le(map, endbit, start + idlen);
0085         if (fragend >= endbit)
0086             goto error;
0087
0088         if (start == freelink) {
0089             freelink += frag & 0x7fff;
0090         } else if (frag == frag_id) {
0091             unsigned int length = fragend + 1 - start;
0092
0093             if (*offset < length)
0094                 return start + *offset;
0095             *offset -= length;
0096         }
0097
0098         start = fragend + 1;
0099     } while (start < endbit);
0100     return -1;
0101
0102 error:
0103     printk(KERN_ERR "adfs: oversized fragment 0x%x at 0x%x-0x%x\n",
0104         frag, start, fragend);
0105     return -1;
0106 }
0107
0108 /*
0109  * Scan the free space map, for this zone, calculating the total
0110  * number of map bits in each free space fragment.
0111  *
0112  * Note: idmask is limited to 15 bits [3.2]
0113  */
0114 static unsigned int
0115 scan_free_map(struct adfs_sb_info *asb, struct adfs_discmap *dm)
0116 {
0117     const unsigned int endbit = dm->dm_endbit;
0118     const unsigned int idlen  = asb->s_idlen;
0119     const unsigned int frag_idlen = idlen <= 15 ? idlen : 15;
0120     const u32 idmask = (1 << frag_idlen) - 1;
0121     unsigned char *map = dm->dm_bh->b_data;
0122     unsigned int start = 8, fragend;
0123     u32 frag;
0124     unsigned long total = 0;
0125
0126     /*
0127      * get fragment id
0128      */
0129     frag = GET_FRAG_ID(map, start, idmask);
0130
0131     /*
0132      * If the freelink is null, then no free fragments
0133      * exist in this zone.
0134      */
0135     if (frag == 0)
0136         return 0;
0137
0138     do {
0139         start += frag;
0140
0141         frag = GET_FRAG_ID(map, start, idmask);
0142
0143         fragend = find_next_bit_le(map, endbit, start + idlen);
0144         if (fragend >= endbit)
0145             goto error;
0146
0147         total += fragend + 1 - start;
0148     } while (frag >= idlen + 1);
0149
0150     if (frag != 0)
0151         printk(KERN_ERR "adfs: undersized free fragment\n");
0152
0153     return total;
0154 error:
0155     printk(KERN_ERR "adfs: oversized free fragment\n");
0156     return 0;
0157 }
0158
0159 static int scan_map(struct adfs_sb_info *asb, unsigned int zone,
0160             const u32 frag_id, unsigned int mapoff)
0161 {
0162     const unsigned int idlen = asb->s_idlen;
0163     struct adfs_discmap *dm, *dm_end;
0164     int result;
0165
0166     dm  = asb->s_map + zone;
0167     zone    = asb->s_map_size;
0168     dm_end  = asb->s_map + zone;
0169
0170     do {
0171         result = lookup_zone(dm, idlen, frag_id, &mapoff);
0172
0173         if (result != -1)
0174             goto found;
0175
0176         dm ++;
0177         if (dm == dm_end)
0178             dm = asb->s_map;
0179     } while (--zone > 0);
0180
0181     return -1;
0182 found:
0183     result -= dm->dm_startbit;
0184     result += dm->dm_startblk;
0185
0186     return result;
0187 }
0188
0189 /*
0190  * calculate the amount of free blocks in the map.
0191  *
0192  *              n=1
0193  *  total_free = E(free_in_zone_n)
0194  *              nzones
0195  */
0196 void adfs_map_statfs(struct super_block *sb, struct kstatfs *buf)
0197 {
0198     struct adfs_sb_info *asb = ADFS_SB(sb);
0199     struct adfs_discrecord *dr = adfs_map_discrecord(asb->s_map);
0200     struct adfs_discmap *dm;
0201     unsigned int total = 0;
0202     unsigned int zone;
0203
0204     dm   = asb->s_map;
0205     zone = asb->s_map_size;
0206
0207     do {
0208         total += scan_free_map(asb, dm++);
0209     } while (--zone > 0);
0210
0211     buf->f_blocks  = adfs_disc_size(dr) >> sb->s_blocksize_bits;
0212     buf->f_files   = asb->s_ids_per_zone * asb->s_map_size;
0213     buf->f_bavail  =
0214     buf->f_bfree   = signed_asl(total, asb->s_map2blk);
0215 }
0216
0217 int adfs_map_lookup(struct super_block *sb, u32 frag_id, unsigned int offset)
0218 {
0219     struct adfs_sb_info *asb = ADFS_SB(sb);
0220     unsigned int zone, mapoff;
0221     int result;
0222
0223     /*
0224      * map & root fragment is special - it starts in the center of the
0225      * disk.  The other fragments start at zone (frag / ids_per_zone)
0226      */
0227     if (frag_id == ADFS_ROOT_FRAG)
0228         zone = asb->s_map_size >> 1;
0229     else
0230         zone = frag_id / asb->s_ids_per_zone;
0231
0232     if (zone >= asb->s_map_size)
0233         goto bad_fragment;
0234
0235     /* Convert sector offset to map offset */
0236     mapoff = signed_asl(offset, -asb->s_map2blk);
0237
0238     read_lock(&adfs_map_lock);
0239     result = scan_map(asb, zone, frag_id, mapoff);
0240     read_unlock(&adfs_map_lock);
0241
0242     if (result > 0) {
0243         unsigned int secoff;
0244
0245         /* Calculate sector offset into map block */
0246         secoff = offset - signed_asl(mapoff, asb->s_map2blk);
0247         return secoff + signed_asl(result, asb->s_map2blk);
0248     }
0249
0250     adfs_error(sb, "fragment 0x%04x at offset %d not found in map",
0251            frag_id, offset);
0252     return 0;
0253
0254 bad_fragment:
0255     adfs_error(sb, "invalid fragment 0x%04x (zone = %d, max = %d)",
0256            frag_id, zone, asb->s_map_size);
0257     return 0;
0258 }
0259
0260 static unsigned char adfs_calczonecheck(struct super_block *sb, unsigned char *map)
0261 {
0262     unsigned int v0, v1, v2, v3;
0263     int i;
0264
0265     v0 = v1 = v2 = v3 = 0;
0266     for (i = sb->s_blocksize - 4; i; i -= 4) {
0267         v0 += map[i]     + (v3 >> 8);
0268         v3 &= 0xff;
0269         v1 += map[i + 1] + (v0 >> 8);
0270         v0 &= 0xff;
0271         v2 += map[i + 2] + (v1 >> 8);
0272         v1 &= 0xff;
0273         v3 += map[i + 3] + (v2 >> 8);
0274         v2 &= 0xff;
0275     }
0276     v0 +=           v3 >> 8;
0277     v1 += map[1] + (v0 >> 8);
0278     v2 += map[2] + (v1 >> 8);
0279     v3 += map[3] + (v2 >> 8);
0280
0281     return v0 ^ v1 ^ v2 ^ v3;
0282 }
0283
0284 static int adfs_checkmap(struct super_block *sb, struct adfs_discmap *dm)
0285 {
0286     unsigned char crosscheck = 0, zonecheck = 1;
0287     int i;
0288
0289     for (i = 0; i < ADFS_SB(sb)->s_map_size; i++) {
0290         unsigned char *map;
0291
0292         map = dm[i].dm_bh->b_data;
0293
0294         if (adfs_calczonecheck(sb, map) != map[0]) {
0295             adfs_error(sb, "zone %d fails zonecheck", i);
0296             zonecheck = 0;
0297         }
0298         crosscheck ^= map[3];
0299     }
0300     if (crosscheck != 0xff)
0301         adfs_error(sb, "crosscheck != 0xff");
0302     return crosscheck == 0xff && zonecheck;
0303 }
0304
0305 /*
0306  * Layout the map - the first zone contains a copy of the disc record,
0307  * and the last zone must be limited to the size of the filesystem.
0308  */
0309 static void adfs_map_layout(struct adfs_discmap *dm, unsigned int nzones,
0310                 struct adfs_discrecord *dr)
0311 {
0312     unsigned int zone, zone_size;
0313     u64 size;
0314
0315     zone_size = (8 << dr->log2secsize) - le16_to_cpu(dr->zone_spare);
0316
0317     dm[0].dm_bh       = NULL;
0318     dm[0].dm_startblk = 0;
0319     dm[0].dm_startbit = 32 + ADFS_DR_SIZE_BITS;
0320     dm[0].dm_endbit   = 32 + zone_size;
0321
0322     for (zone = 1; zone < nzones; zone++) {
0323         dm[zone].dm_bh       = NULL;
0324         dm[zone].dm_startblk = zone * zone_size - ADFS_DR_SIZE_BITS;
0325         dm[zone].dm_startbit = 32;
0326         dm[zone].dm_endbit   = 32 + zone_size;
0327     }
0328
0329     size = adfs_disc_size(dr) >> dr->log2bpmb;
0330     size -= (nzones - 1) * zone_size - ADFS_DR_SIZE_BITS;
0331     dm[nzones - 1].dm_endbit = 32 + size;
0332 }
0333
0334 static int adfs_map_read(struct adfs_discmap *dm, struct super_block *sb,
0335              unsigned int map_addr, unsigned int nzones)
0336 {
0337     unsigned int zone;
0338
0339     for (zone = 0; zone < nzones; zone++) {
0340         dm[zone].dm_bh = sb_bread(sb, map_addr + zone);
0341         if (!dm[zone].dm_bh)
0342             return -EIO;
0343     }
0344
0345     return 0;
0346 }
0347
0348 static void adfs_map_relse(struct adfs_discmap *dm, unsigned int nzones)
0349 {
0350     unsigned int zone;
0351
0352     for (zone = 0; zone < nzones; zone++)
0353         brelse(dm[zone].dm_bh);
0354 }
0355
0356 struct adfs_discmap *adfs_read_map(struct super_block *sb, struct adfs_discrecord *dr)
0357 {
0358     struct adfs_sb_info *asb = ADFS_SB(sb);
0359     struct adfs_discmap *dm;
0360     unsigned int map_addr, zone_size, nzones;
0361     int ret;
0362
0363     nzones    = dr->nzones | dr->nzones_high << 8;
0364     zone_size = (8 << dr->log2secsize) - le16_to_cpu(dr->zone_spare);
0365
0366     asb->s_idlen = dr->idlen;
0367     asb->s_map_size = nzones;
0368     asb->s_map2blk = dr->log2bpmb - dr->log2secsize;
0369     asb->s_log2sharesize = dr->log2sharesize;
0370     asb->s_ids_per_zone = zone_size / (asb->s_idlen + 1);
0371
0372     map_addr = (nzones >> 1) * zone_size -
0373              ((nzones > 1) ? ADFS_DR_SIZE_BITS : 0);
0374     map_addr = signed_asl(map_addr, asb->s_map2blk);
0375
0376     dm = kmalloc_array(nzones, sizeof(*dm), GFP_KERNEL);
0377     if (dm == NULL) {
0378         adfs_error(sb, "not enough memory");
0379         return ERR_PTR(-ENOMEM);
0380     }
0381
0382     adfs_map_layout(dm, nzones, dr);
0383
0384     ret = adfs_map_read(dm, sb, map_addr, nzones);
0385     if (ret) {
0386         adfs_error(sb, "unable to read map");
0387         goto error_free;
0388     }
0389
0390     if (adfs_checkmap(sb, dm))
0391         return dm;
0392
0393     adfs_error(sb, "map corrupted");
0394
0395 error_free:
0396     adfs_map_relse(dm, nzones);
0397     kfree(dm);
0398     return ERR_PTR(-EIO);
0399 }
0400
0401 void adfs_free_map(struct super_block *sb)
0402 {
0403     struct adfs_sb_info *asb = ADFS_SB(sb);
0404
0405     adfs_map_relse(asb->s_map, asb->s_map_size);
0406     kfree(asb->s_map);
0407 }