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/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;
 }
	// SPDX-License-Identifier: GPL-2.0-only
	/*
	* linux/fs/adfs/map.c
	*
	* Copyright (C) 1997-2002 Russell King
	*/
	#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;
	}