linux/fs/adfs/map.c

// 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) …

/*
 * 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)
{ … }

/*
 * 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)
{ … }

static int scan_map(struct adfs_sb_info *asb, unsigned int zone,
		    const u32 frag_id, unsigned int mapoff)
{ … }

/*
 * 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)
{ … }

int adfs_map_lookup(struct super_block *sb, u32 frag_id, unsigned int offset)
{ … }

static unsigned char adfs_calczonecheck(struct super_block *sb, unsigned char *map)
{ … }

static int adfs_checkmap(struct super_block *sb, struct adfs_discmap *dm)
{ … }

/*
 * 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)
{ … }

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

static void adfs_map_relse(struct adfs_discmap *dm, unsigned int nzones)
{ … }

struct adfs_discmap *adfs_read_map(struct super_block *sb, struct adfs_discrecord *dr)
{ … }

void adfs_free_map(struct super_block *sb)
{ … }