text: // 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);
  }
  