fs/adfs/map.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  *  linux/fs/adfs/map.c
  *
  *  Copyright (C) 1997-2002 Russell King
  */
 #include <linux/slab.h>
 #include <linux/statfs.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 u32 frag_id, unsigned int *offset)
 {
 	const unsigned int endbit = dm->dm_endbit;
 	const u32 idmask = (1 << idlen) - 1;
 	unsigned char *map = dm->dm_bh->b_data;
 	unsigned int start = dm->dm_startbit;
 	unsigned int freelink, fragend;
 	u32 frag;

 	frag = GET_FRAG_ID(map, 8, idmask & 0x7fff);
 	freelink = frag ? 8 + frag : 0;

 	do {
 		frag = GET_FRAG_ID(map, start, idmask);

 		fragend = find_next_bit_le(map, endbit, start + idlen);
 		if (fragend >= endbit)
 			goto error;

 		if (start == freelink) {
 			freelink += frag & 0x7fff;
 		} else if (frag == frag_id) {
 			unsigned int length = fragend + 1 - start;

 			if (*offset < length)
 				return start + *offset;
 			*offset -= length;
 		}

 		start = fragend + 1;
 	} while (start < endbit);
 	return -1;

 error:
 	printk(KERN_ERR "adfs: oversized fragment 0x%x at 0x%x-0x%x\n",
 		frag, start, fragend);
 	return -1;
 }

 /*
  * 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 endbit = dm->dm_endbit;
 	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, fragend;
 	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;

 		frag = GET_FRAG_ID(map, start, idmask);

 		fragend = find_next_bit_le(map, endbit, start + idlen);
 		if (fragend >= endbit)
 			goto error;

 		total += fragend + 1 - 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 u32 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
  */
 void adfs_map_statfs(struct super_block *sb, struct kstatfs *buf)
 {
 	struct adfs_sb_info *asb = ADFS_SB(sb);
 	struct adfs_discrecord *dr = adfs_map_discrecord(asb->s_map);
 	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);

 	buf->f_blocks  = adfs_disc_size(dr) >> sb->s_blocksize_bits;
 	buf->f_files   = asb->s_ids_per_zone * asb->s_map_size;
 	buf->f_bavail  =
 	buf->f_bfree   = signed_asl(total, asb->s_map2blk);
 }

 int adfs_map_lookup(struct super_block *sb, u32 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;
 }

 static unsigned char adfs_calczonecheck(struct super_block *sb, unsigned char *map)
 {
 	unsigned int v0, v1, v2, v3;
 	int i;

 	v0 = v1 = v2 = v3 = 0;
 	for (i = sb->s_blocksize - 4; i; i -= 4) {
 		v0 += map[i]     + (v3 >> 8);
 		v3 &= 0xff;
 		v1 += map[i + 1] + (v0 >> 8);
 		v0 &= 0xff;
 		v2 += map[i + 2] + (v1 >> 8);
 		v1 &= 0xff;
 		v3 += map[i + 3] + (v2 >> 8);
 		v2 &= 0xff;
 	}
 	v0 +=           v3 >> 8;
 	v1 += map[1] + (v0 >> 8);
 	v2 += map[2] + (v1 >> 8);
 	v3 += map[3] + (v2 >> 8);

 	return v0 ^ v1 ^ v2 ^ v3;
 }

 static int adfs_checkmap(struct super_block *sb, struct adfs_discmap *dm)
 {
 	unsigned char crosscheck = 0, zonecheck = 1;
 	int i;

 	for (i = 0; i < ADFS_SB(sb)->s_map_size; i++) {
 		unsigned char *map;

 		map = dm[i].dm_bh->b_data;

 		if (adfs_calczonecheck(sb, map) != map[0]) {
 			adfs_error(sb, "zone %d fails zonecheck", i);
 			zonecheck = 0;
 		}
 		crosscheck ^= map[3];
 	}
 	if (crosscheck != 0xff)
 		adfs_error(sb, "crosscheck != 0xff");
 	return crosscheck == 0xff && zonecheck;
 }

 /*
  * Layout the map - the first zone contains a copy of the disc record,
  * and the last zone must be limited to the size of the filesystem.
  */
 static void adfs_map_layout(struct adfs_discmap *dm, unsigned int nzones,
 			    struct adfs_discrecord *dr)
 {
 	unsigned int zone, zone_size;
 	u64 size;

 	zone_size = (8 << dr->log2secsize) - le16_to_cpu(dr->zone_spare);

 	dm[0].dm_bh       = NULL;
 	dm[0].dm_startblk = 0;
 	dm[0].dm_startbit = 32 + ADFS_DR_SIZE_BITS;
 	dm[0].dm_endbit   = 32 + zone_size;

 	for (zone = 1; zone < nzones; zone++) {
 		dm[zone].dm_bh       = NULL;
 		dm[zone].dm_startblk = zone * zone_size - ADFS_DR_SIZE_BITS;
 		dm[zone].dm_startbit = 32;
 		dm[zone].dm_endbit   = 32 + zone_size;
 	}

 	size = adfs_disc_size(dr) >> dr->log2bpmb;
 	size -= (nzones - 1) * zone_size - ADFS_DR_SIZE_BITS;
 	dm[nzones - 1].dm_endbit = 32 + size;
 }

 static int adfs_map_read(struct adfs_discmap *dm, struct super_block *sb,
 			 unsigned int map_addr, unsigned int nzones)
 {
 	unsigned int zone;

 	for (zone = 0; zone < nzones; zone++) {
 		dm[zone].dm_bh = sb_bread(sb, map_addr + zone);
 		if (!dm[zone].dm_bh)
 			return -EIO;
 	}

 	return 0;
 }

 static void adfs_map_relse(struct adfs_discmap *dm, unsigned int nzones)
 {
 	unsigned int zone;

 	for (zone = 0; zone < nzones; zone++)
 		brelse(dm[zone].dm_bh);
 }

 struct adfs_discmap *adfs_read_map(struct super_block *sb, struct adfs_discrecord *dr)
 {
 	struct adfs_sb_info *asb = ADFS_SB(sb);
 	struct adfs_discmap *dm;
 	unsigned int map_addr, zone_size, nzones;
 	int ret;

 	nzones    = dr->nzones | dr->nzones_high << 8;
 	zone_size = (8 << dr->log2secsize) - le16_to_cpu(dr->zone_spare);

 	asb->s_idlen = dr->idlen;
 	asb->s_map_size = nzones;
 	asb->s_map2blk = dr->log2bpmb - dr->log2secsize;
 	asb->s_log2sharesize = dr->log2sharesize;
 	asb->s_ids_per_zone = zone_size / (asb->s_idlen + 1);

 	map_addr = (nzones >> 1) * zone_size -
 		     ((nzones > 1) ? ADFS_DR_SIZE_BITS : 0);
 	map_addr = signed_asl(map_addr, asb->s_map2blk);

 	dm = kmalloc_array(nzones, sizeof(*dm), GFP_KERNEL);
 	if (dm == NULL) {
 		adfs_error(sb, "not enough memory");
 		return ERR_PTR(-ENOMEM);
 	}

 	adfs_map_layout(dm, nzones, dr);

 	ret = adfs_map_read(dm, sb, map_addr, nzones);
 	if (ret) {
 		adfs_error(sb, "unable to read map");
 		goto error_free;
 	}

 	if (adfs_checkmap(sb, dm))
 		return dm;

 	adfs_error(sb, "map corrupted");

 error_free:
 	adfs_map_relse(dm, nzones);
 	kfree(dm);
 	return ERR_PTR(-EIO);
 }

 void adfs_free_map(struct super_block *sb)
 {
 	struct adfs_sb_info *asb = ADFS_SB(sb);

 	adfs_map_relse(asb->s_map, asb->s_map_size);
 	kfree(asb->s_map);
 }
	// SPDX-License-Identifier: GPL-2.0-only
	/*
	* linux/fs/adfs/map.c
	*
	* Copyright (C) 1997-2002 Russell King
	*/
	#include <linux/slab.h>
	#include <linux/statfs.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 u32 frag_id, unsigned int *offset)
	{
	const unsigned int endbit = dm->dm_endbit;
	const u32 idmask = (1 << idlen) - 1;
	unsigned char *map = dm->dm_bh->b_data;
	unsigned int start = dm->dm_startbit;
	unsigned int freelink, fragend;
	u32 frag;

	frag = GET_FRAG_ID(map, 8, idmask & 0x7fff);
	freelink = frag ? 8 + frag : 0;

	do {
	frag = GET_FRAG_ID(map, start, idmask);

	fragend = find_next_bit_le(map, endbit, start + idlen);
	if (fragend >= endbit)
	goto error;

	if (start == freelink) {
	freelink += frag & 0x7fff;
	} else if (frag == frag_id) {
	unsigned int length = fragend + 1 - start;

	if (*offset < length)
	return start + *offset;
	*offset -= length;
	}

	start = fragend + 1;
	} while (start < endbit);
	return -1;

	error:
	printk(KERN_ERR "adfs: oversized fragment 0x%x at 0x%x-0x%x\n",
	frag, start, fragend);
	return -1;
	}

	/*
	* 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 endbit = dm->dm_endbit;
	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, fragend;
	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;

	frag = GET_FRAG_ID(map, start, idmask);

	fragend = find_next_bit_le(map, endbit, start + idlen);
	if (fragend >= endbit)
	goto error;

	total += fragend + 1 - 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 u32 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
	*/
	void adfs_map_statfs(struct super_block sb, struct kstatfs buf)
	{
	struct adfs_sb_info *asb = ADFS_SB(sb);
	struct adfs_discrecord *dr = adfs_map_discrecord(asb->s_map);
	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);

	buf->f_blocks = adfs_disc_size(dr) >> sb->s_blocksize_bits;
	buf->f_files = asb->s_ids_per_zone * asb->s_map_size;
	buf->f_bavail =
	buf->f_bfree = signed_asl(total, asb->s_map2blk);
	}

	int adfs_map_lookup(struct super_block *sb, u32 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;
	}

	static unsigned char adfs_calczonecheck(struct super_block sb, unsigned char map)
	{
	unsigned int v0, v1, v2, v3;
	int i;

	v0 = v1 = v2 = v3 = 0;
	for (i = sb->s_blocksize - 4; i; i -= 4) {
	v0 += map[i] + (v3 >> 8);
	v3 &= 0xff;
	v1 += map[i + 1] + (v0 >> 8);
	v0 &= 0xff;
	v2 += map[i + 2] + (v1 >> 8);
	v1 &= 0xff;
	v3 += map[i + 3] + (v2 >> 8);
	v2 &= 0xff;
	}
	v0 += v3 >> 8;
	v1 += map[1] + (v0 >> 8);
	v2 += map[2] + (v1 >> 8);
	v3 += map[3] + (v2 >> 8);

	return v0 ^ v1 ^ v2 ^ v3;
	}

	static int adfs_checkmap(struct super_block sb, struct adfs_discmap dm)
	{
	unsigned char crosscheck = 0, zonecheck = 1;
	int i;

	for (i = 0; i < ADFS_SB(sb)->s_map_size; i++) {
	unsigned char *map;

	map = dm[i].dm_bh->b_data;

	if (adfs_calczonecheck(sb, map) != map[0]) {
	adfs_error(sb, "zone %d fails zonecheck", i);
	zonecheck = 0;
	}
	crosscheck ^= map[3];
	}
	if (crosscheck != 0xff)
	adfs_error(sb, "crosscheck != 0xff");
	return crosscheck == 0xff && zonecheck;
	}

	/*
	* Layout the map - the first zone contains a copy of the disc record,
	* and the last zone must be limited to the size of the filesystem.
	*/
	static void adfs_map_layout(struct adfs_discmap *dm, unsigned int nzones,
	struct adfs_discrecord *dr)
	{
	unsigned int zone, zone_size;
	u64 size;

	zone_size = (8 << dr->log2secsize) - le16_to_cpu(dr->zone_spare);

	dm[0].dm_bh = NULL;
	dm[0].dm_startblk = 0;
	dm[0].dm_startbit = 32 + ADFS_DR_SIZE_BITS;
	dm[0].dm_endbit = 32 + zone_size;

	for (zone = 1; zone < nzones; zone++) {
	dm[zone].dm_bh = NULL;
	dm[zone].dm_startblk = zone * zone_size - ADFS_DR_SIZE_BITS;
	dm[zone].dm_startbit = 32;
	dm[zone].dm_endbit = 32 + zone_size;
	}

	size = adfs_disc_size(dr) >> dr->log2bpmb;
	size -= (nzones - 1) * zone_size - ADFS_DR_SIZE_BITS;
	dm[nzones - 1].dm_endbit = 32 + size;
	}

	static int adfs_map_read(struct adfs_discmap dm, struct super_block sb,
	unsigned int map_addr, unsigned int nzones)
	{
	unsigned int zone;

	for (zone = 0; zone < nzones; zone++) {
	dm[zone].dm_bh = sb_bread(sb, map_addr + zone);
	if (!dm[zone].dm_bh)
	return -EIO;
	}

	return 0;
	}

	static void adfs_map_relse(struct adfs_discmap *dm, unsigned int nzones)
	{
	unsigned int zone;

	for (zone = 0; zone < nzones; zone++)
	brelse(dm[zone].dm_bh);
	}

	struct adfs_discmap adfs_read_map(struct super_block sb, struct adfs_discrecord *dr)
	{
	struct adfs_sb_info *asb = ADFS_SB(sb);
	struct adfs_discmap *dm;
	unsigned int map_addr, zone_size, nzones;
	int ret;

	nzones = dr->nzones \| dr->nzones_high << 8;
	zone_size = (8 << dr->log2secsize) - le16_to_cpu(dr->zone_spare);

	asb->s_idlen = dr->idlen;
	asb->s_map_size = nzones;
	asb->s_map2blk = dr->log2bpmb - dr->log2secsize;
	asb->s_log2sharesize = dr->log2sharesize;
	asb->s_ids_per_zone = zone_size / (asb->s_idlen + 1);

	map_addr = (nzones >> 1) * zone_size -
	((nzones > 1) ? ADFS_DR_SIZE_BITS : 0);
	map_addr = signed_asl(map_addr, asb->s_map2blk);

	dm = kmalloc_array(nzones, sizeof(*dm), GFP_KERNEL);
	if (dm == NULL) {
	adfs_error(sb, "not enough memory");
	return ERR_PTR(-ENOMEM);
	}

	adfs_map_layout(dm, nzones, dr);

	ret = adfs_map_read(dm, sb, map_addr, nzones);
	if (ret) {
	adfs_error(sb, "unable to read map");
	goto error_free;
	}

	if (adfs_checkmap(sb, dm))
	return dm;

	adfs_error(sb, "map corrupted");

	error_free:
	adfs_map_relse(dm, nzones);
	kfree(dm);
	return ERR_PTR(-EIO);
	}

	void adfs_free_map(struct super_block *sb)
	{
	struct adfs_sb_info *asb = ADFS_SB(sb);

	adfs_map_relse(asb->s_map, asb->s_map_size);
	kfree(asb->s_map);
	}