map.c

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/*
 *  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;
}