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