283 строки
6.7 KiB
C
283 строки
6.7 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* linux/fs/adfs/map.c
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*
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* Copyright (C) 1997-2002 Russell King
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*/
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#include <asm/unaligned.h>
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#include "adfs.h"
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/*
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* The ADFS map is basically a set of sectors. Each sector is called a
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* zone which contains a bitstream made up of variable sized fragments.
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* Each bit refers to a set of bytes in the filesystem, defined by
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* log2bpmb. This may be larger or smaller than the sector size, but
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* the overall size it describes will always be a round number of
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* sectors. A fragment id is always idlen bits long.
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*
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* < idlen > < n > <1>
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* +---------+-------//---------+---+
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* | frag id | 0000....000000 | 1 |
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* +---------+-------//---------+---+
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*
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* The physical disk space used by a fragment is taken from the start of
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* the fragment id up to and including the '1' bit - ie, idlen + n + 1
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* bits.
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*
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* A fragment id can be repeated multiple times in the whole map for
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* large or fragmented files. The first map zone a fragment starts in
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* is given by fragment id / ids_per_zone - this allows objects to start
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* from any zone on the disk.
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*
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* Free space is described by a linked list of fragments. Each free
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* fragment describes free space in the same way as the other fragments,
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* however, the frag id specifies an offset (in map bits) from the end
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* of this fragment to the start of the next free fragment.
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*
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* Objects stored on the disk are allocated object ids (we use these as
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* our inode numbers.) Object ids contain a fragment id and an optional
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* offset. This allows a directory fragment to contain small files
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* associated with that directory.
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*/
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/*
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* For the future...
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*/
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static DEFINE_RWLOCK(adfs_map_lock);
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/*
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* This is fun. We need to load up to 19 bits from the map at an
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* arbitrary bit alignment. (We're limited to 19 bits by F+ version 2).
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*/
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#define GET_FRAG_ID(_map,_start,_idmask) \
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({ \
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unsigned char *_m = _map + (_start >> 3); \
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u32 _frag = get_unaligned_le32(_m); \
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_frag >>= (_start & 7); \
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_frag & _idmask; \
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})
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/*
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* return the map bit offset of the fragment frag_id in the zone dm.
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* Note that the loop is optimised for best asm code - look at the
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* output of:
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* gcc -D__KERNEL__ -O2 -I../../include -o - -S map.c
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*/
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static int lookup_zone(const struct adfs_discmap *dm, const unsigned int idlen,
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const u32 frag_id, unsigned int *offset)
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{
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const unsigned int mapsize = dm->dm_endbit;
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const u32 idmask = (1 << idlen) - 1;
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unsigned char *map = dm->dm_bh->b_data + 4;
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unsigned int start = dm->dm_startbit;
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unsigned int mapptr;
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u32 frag;
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do {
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frag = GET_FRAG_ID(map, start, idmask);
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mapptr = start + idlen;
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/*
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* find end of fragment
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*/
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{
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__le32 *_map = (__le32 *)map;
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u32 v = le32_to_cpu(_map[mapptr >> 5]) >> (mapptr & 31);
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while (v == 0) {
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mapptr = (mapptr & ~31) + 32;
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if (mapptr >= mapsize)
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goto error;
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v = le32_to_cpu(_map[mapptr >> 5]);
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}
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mapptr += 1 + ffz(~v);
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}
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if (frag == frag_id)
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goto found;
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again:
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start = mapptr;
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} while (mapptr < mapsize);
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return -1;
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error:
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printk(KERN_ERR "adfs: oversized fragment 0x%x at 0x%x-0x%x\n",
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frag, start, mapptr);
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return -1;
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found:
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{
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int length = mapptr - start;
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if (*offset >= length) {
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*offset -= length;
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goto again;
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}
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}
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return start + *offset;
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}
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/*
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* Scan the free space map, for this zone, calculating the total
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* number of map bits in each free space fragment.
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*
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* Note: idmask is limited to 15 bits [3.2]
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*/
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static unsigned int
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scan_free_map(struct adfs_sb_info *asb, struct adfs_discmap *dm)
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{
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const unsigned int mapsize = dm->dm_endbit + 32;
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const unsigned int idlen = asb->s_idlen;
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const unsigned int frag_idlen = idlen <= 15 ? idlen : 15;
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const u32 idmask = (1 << frag_idlen) - 1;
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unsigned char *map = dm->dm_bh->b_data;
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unsigned int start = 8, mapptr;
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u32 frag;
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unsigned long total = 0;
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/*
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* get fragment id
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*/
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frag = GET_FRAG_ID(map, start, idmask);
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/*
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* If the freelink is null, then no free fragments
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* exist in this zone.
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*/
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if (frag == 0)
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return 0;
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do {
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start += frag;
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/*
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* get fragment id
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*/
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frag = GET_FRAG_ID(map, start, idmask);
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mapptr = start + idlen;
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/*
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* find end of fragment
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*/
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{
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__le32 *_map = (__le32 *)map;
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u32 v = le32_to_cpu(_map[mapptr >> 5]) >> (mapptr & 31);
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while (v == 0) {
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mapptr = (mapptr & ~31) + 32;
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if (mapptr >= mapsize)
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goto error;
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v = le32_to_cpu(_map[mapptr >> 5]);
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}
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mapptr += 1 + ffz(~v);
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}
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total += mapptr - start;
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} while (frag >= idlen + 1);
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if (frag != 0)
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printk(KERN_ERR "adfs: undersized free fragment\n");
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return total;
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error:
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printk(KERN_ERR "adfs: oversized free fragment\n");
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return 0;
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}
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static int scan_map(struct adfs_sb_info *asb, unsigned int zone,
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const u32 frag_id, unsigned int mapoff)
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{
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const unsigned int idlen = asb->s_idlen;
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struct adfs_discmap *dm, *dm_end;
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int result;
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dm = asb->s_map + zone;
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zone = asb->s_map_size;
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dm_end = asb->s_map + zone;
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do {
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result = lookup_zone(dm, idlen, frag_id, &mapoff);
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if (result != -1)
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goto found;
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dm ++;
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if (dm == dm_end)
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dm = asb->s_map;
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} while (--zone > 0);
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return -1;
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found:
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result -= dm->dm_startbit;
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result += dm->dm_startblk;
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return result;
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}
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/*
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* calculate the amount of free blocks in the map.
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*
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* n=1
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* total_free = E(free_in_zone_n)
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* nzones
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*/
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unsigned int
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adfs_map_free(struct super_block *sb)
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{
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struct adfs_sb_info *asb = ADFS_SB(sb);
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struct adfs_discmap *dm;
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unsigned int total = 0;
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unsigned int zone;
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dm = asb->s_map;
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zone = asb->s_map_size;
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do {
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total += scan_free_map(asb, dm++);
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} while (--zone > 0);
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return signed_asl(total, asb->s_map2blk);
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}
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int adfs_map_lookup(struct super_block *sb, u32 frag_id, unsigned int offset)
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{
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struct adfs_sb_info *asb = ADFS_SB(sb);
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unsigned int zone, mapoff;
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int result;
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/*
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* map & root fragment is special - it starts in the center of the
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* disk. The other fragments start at zone (frag / ids_per_zone)
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*/
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if (frag_id == ADFS_ROOT_FRAG)
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zone = asb->s_map_size >> 1;
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else
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zone = frag_id / asb->s_ids_per_zone;
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if (zone >= asb->s_map_size)
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goto bad_fragment;
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/* Convert sector offset to map offset */
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mapoff = signed_asl(offset, -asb->s_map2blk);
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read_lock(&adfs_map_lock);
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result = scan_map(asb, zone, frag_id, mapoff);
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read_unlock(&adfs_map_lock);
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if (result > 0) {
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unsigned int secoff;
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/* Calculate sector offset into map block */
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secoff = offset - signed_asl(mapoff, asb->s_map2blk);
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return secoff + signed_asl(result, asb->s_map2blk);
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}
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adfs_error(sb, "fragment 0x%04x at offset %d not found in map",
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frag_id, offset);
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return 0;
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bad_fragment:
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adfs_error(sb, "invalid fragment 0x%04x (zone = %d, max = %d)",
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frag_id, zone, asb->s_map_size);
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return 0;
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}
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