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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/errno.h>

#include <linux/fs.h>

#include <linux/adfs_fs.h>

#include <linux/spinlock.h>

#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

 * arbitary 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((u32 *)_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;

}