text: /*
   *  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
   * 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_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;
  }
  