FreeBSD/Linux Kernel Cross Reference
sys/bsd/ufs/ffs/fs.h

     /*
      * Copyright (c) 2000-2003 Apple Computer, Inc. All rights reserved.
      *
      * @APPLE_LICENSE_HEADER_START@
      * 
      * The contents of this file constitute Original Code as defined in and
      * are subject to the Apple Public Source License Version 1.1 (the
      * "License").  You may not use this file except in compliance with the
      * License.  Please obtain a copy of the License at
     * http://www.apple.com/publicsource and read it before using this file.
     * 
     * This Original Code and all software distributed under the License are
     * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
     * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
     * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
     * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
     * License for the specific language governing rights and limitations
     * under the License.
     * 
     * @APPLE_LICENSE_HEADER_END@
     */
    /* Copyright (c) 1995 NeXT Computer, Inc. All Rights Reserved */
    /*
     * Copyright (c) 1982, 1986, 1993
     *      The Regents of the University of California.  All rights reserved.
     *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. All advertising materials mentioning features or use of this software
     *    must display the following acknowledgement:
     *      This product includes software developed by the University of
     *      California, Berkeley and its contributors.
     * 4. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     *      @(#)fs.h        8.13 (Berkeley) 3/21/95
     */
    #ifndef _FFS_FS_H_
    #define _FFS_FS_H_
    
    #include <sys/appleapiopts.h>
    
    #ifdef __APPLE_API_UNSTABLE
    /*
     * Each disk drive contains some number of file systems.
     * A file system consists of a number of cylinder groups.
     * Each cylinder group has inodes and data.
     *
     * A file system is described by its super-block, which in turn
     * describes the cylinder groups.  The super-block is critical
     * data and is replicated in each cylinder group to protect against
     * catastrophic loss.  This is done at `newfs' time and the critical
     * super-block data does not change, so the copies need not be
     * referenced further unless disaster strikes.
     *
     * For file system fs, the offsets of the various blocks of interest
     * are given in the super block as:
     *      [fs->fs_sblkno]         Super-block
     *      [fs->fs_cblkno]         Cylinder group block
     *      [fs->fs_iblkno]         Inode blocks
     *      [fs->fs_dblkno]         Data blocks
     * The beginning of cylinder group cg in fs, is given by
     * the ``cgbase(fs, cg)'' macro.
     *
     * The first boot and super blocks are given in absolute disk addresses.
     * The byte-offset forms are preferred, as they don't imply a sector size.
     */
    #define BBSIZE          8192
    #define SBSIZE          8192
    #define BBOFF           ((off_t)(0))
    #define SBOFF           ((off_t)(BBOFF + BBSIZE))
    #define BBLOCK          ((ufs_daddr_t)(0))
    #define SBLOCK          ((ufs_daddr_t)(BBLOCK + BBSIZE / DEV_BSIZE))
    
    /*
     * Addresses stored in inodes are capable of addressing fragments
     * of `blocks'. File system blocks of at most size MAXBSIZE can 
     * be optionally broken into 2, 4, or 8 pieces, each of which is
     * addressible; these pieces may be DEV_BSIZE, or some multiple of
     * a DEV_BSIZE unit.
    *
    * Large files consist of exclusively large data blocks.  To avoid
    * undue wasted disk space, the last data block of a small file may be
    * allocated as only as many fragments of a large block as are
    * necessary.  The file system format retains only a single pointer
    * to such a fragment, which is a piece of a single large block that
    * has been divided.  The size of such a fragment is determinable from
    * information in the inode, using the ``blksize(fs, ip, lbn)'' macro.
    *
    * The file system records space availability at the fragment level;
    * to determine block availability, aligned fragments are examined.
    */
   
   /*
    * MINBSIZE is the smallest allowable block size.
    * In order to insure that it is possible to create files of size
    * 2^32 with only two levels of indirection, MINBSIZE is set to 4096.
    * MINBSIZE must be big enough to hold a cylinder group block,
    * thus changes to (struct cg) must keep its size within MINBSIZE.
    * Note that super blocks are always of size SBSIZE,
    * and that both SBSIZE and MAXBSIZE must be >= MINBSIZE.
    */
   #define MINBSIZE        4096
   
   /*
    * The path name on which the file system is mounted is maintained
    * in fs_fsmnt. MAXMNTLEN defines the amount of space allocated in 
    * the super block for this name.
    */
   #define MAXMNTLEN       512
   
   /*
    * The limit on the amount of summary information per file system
    * is defined by MAXCSBUFS. It is currently parameterized for a
    * size of 128 bytes (2 million cylinder groups on machines with
    * 32-bit pointers, and 1 million on 64-bit machines). One pointer
    * is taken away to point to an array of cluster sizes that is
    * computed as cylinder groups are inspected.
    * There is a 128-byte region in the superblock reserved for in-core
    * pointers to summary information. Originally this included an array
    * of pointers to blocks of struct csum; now there are just three
    * pointers and the remaining space is padded with fs_ocsp[].
    *
    * NOCSPTRS determines the size of this padding. One pointer (fs_csp)
    * is taken away to point to a contiguous array of struct csum for
    * all cylinder groups; a second (fs_maxcluster) points to an array
    * of cluster sizes that is computed as cylinder groups are inspected,
    * and the third points to an array that tracks the creation of new
    * directories.
    */
   #define NOCSPTRS ((128 / sizeof(void *)) - 3)
   
   /*
    * A summary of contiguous blocks of various sizes is maintained
    * in each cylinder group. Normally this is set by the initial
    * value of fs_maxcontig. To conserve space, a maximum summary size
    * is set by FS_MAXCONTIG.
    */
   #define FS_MAXCONTIG    16
   
   /*
    * MINFREE gives the minimum acceptable percentage of file system
    * blocks which may be free. If the freelist drops below this level
    * only the superuser may continue to allocate blocks. This may
    * be set to 0 if no reserve of free blocks is deemed necessary,
    * however throughput drops by fifty percent if the file system
    * is run at between 95% and 100% full; thus the minimum default
    * value of fs_minfree is 5%. However, to get good clustering
    * performance, 10% is a better choice. hence we use 10% as our
    * default value. With 10% free space, fragmentation is not a
    * problem, so we choose to optimize for time.
    */
   #define MINFREE         5
   #define DEFAULTOPT      FS_OPTTIME
   
   /* Grigoriy Orlov <gluk@ptci.ru> has done some extensive work to fine
    * tune the layout preferences for directories within a filesystem.
    * His algorithm can be tuned by adjusting the following parameters
    * which tell the system the average file size and the average number
    * of files per directory. These defaults are well selected for typical
    * filesystems, but may need to be tuned for odd cases like filesystems
    * being used for squid caches or news spools.
    */
   #define AVFILESIZ       16384
   #define AFPDIR          64
   
   /*
    * Per cylinder group information; summarized in blocks allocated
    * from first cylinder group data blocks.  These blocks have to be
    * read in from fs_csaddr (size fs_cssize) in addition to the
    * super block.
    */
   struct csum {
           int32_t cs_ndir;                /* number of directories */
           int32_t cs_nbfree;              /* number of free blocks */
           int32_t cs_nifree;              /* number of free inodes */
           int32_t cs_nffree;              /* number of free frags */
   };
   
   /*
    * Super block for an FFS file system.
    */
   struct fs {
           int32_t  fs_firstfield;         /* historic file system linked list, */
           int32_t  fs_unused_1;           /*     used for incore super blocks */
           ufs_daddr_t fs_sblkno;          /* addr of super-block in filesys */
           ufs_daddr_t fs_cblkno;          /* offset of cyl-block in filesys */
           ufs_daddr_t fs_iblkno;          /* offset of inode-blocks in filesys */
           ufs_daddr_t fs_dblkno;          /* offset of first data after cg */
           int32_t  fs_cgoffset;           /* cylinder group offset in cylinder */
           int32_t  fs_cgmask;             /* used to calc mod fs_ntrak */
           time_t   fs_time;               /* last time written */
           int32_t  fs_size;               /* number of blocks in fs */
           int32_t  fs_dsize;              /* number of data blocks in fs */
           int32_t  fs_ncg;                /* number of cylinder groups */
           int32_t  fs_bsize;              /* size of basic blocks in fs */
           int32_t  fs_fsize;              /* size of frag blocks in fs */
           int32_t  fs_frag;               /* number of frags in a block in fs */
   /* these are configuration parameters */
           int32_t  fs_minfree;            /* minimum percentage of free blocks */
           int32_t  fs_rotdelay;           /* num of ms for optimal next block */
           int32_t  fs_rps;                /* disk revolutions per second */
   /* these fields can be computed from the others */
           int32_t  fs_bmask;              /* ``blkoff'' calc of blk offsets */
           int32_t  fs_fmask;              /* ``fragoff'' calc of frag offsets */
           int32_t  fs_bshift;             /* ``lblkno'' calc of logical blkno */
           int32_t  fs_fshift;             /* ``numfrags'' calc number of frags */
   /* these are configuration parameters */
           int32_t  fs_maxcontig;          /* max number of contiguous blks */
           int32_t  fs_maxbpg;             /* max number of blks per cyl group */
   /* these fields can be computed from the others */
           int32_t  fs_fragshift;          /* block to frag shift */
           int32_t  fs_fsbtodb;            /* fsbtodb and dbtofsb shift constant */
           int32_t  fs_sbsize;             /* actual size of super block */
           int32_t  fs_csmask;             /* csum block offset (now unused) */
           int32_t  fs_csshift;            /* csum block number (now unused) */
           int32_t  fs_nindir;             /* value of NINDIR */
           int32_t  fs_inopb;              /* value of INOPB */
           int32_t  fs_nspf;               /* value of NSPF */
   /* yet another configuration parameter */
           int32_t  fs_optim;              /* optimization preference, see below */
   /* these fields are derived from the hardware */
           int32_t  fs_npsect;             /* # sectors/track including spares */
           int32_t  fs_interleave;         /* hardware sector interleave */
           int32_t  fs_trackskew;          /* sector 0 skew, per track */
           int32_t  fs_headswitch;         /* head switch time, usec */
           int32_t  fs_trkseek;            /* track-to-track seek, usec */
   /* sizes determined by number of cylinder groups and their sizes */
           ufs_daddr_t fs_csaddr;          /* blk addr of cyl grp summary area */
           int32_t  fs_cssize;             /* size of cyl grp summary area */
           int32_t  fs_cgsize;             /* cylinder group size */
   /* these fields are derived from the hardware */
           int32_t  fs_ntrak;              /* tracks per cylinder */
           int32_t  fs_nsect;              /* sectors per track */
           int32_t  fs_spc;                        /* sectors per cylinder */
   /* this comes from the disk driver partitioning */
           int32_t  fs_ncyl;               /* cylinders in file system */
   /* these fields can be computed from the others */
           int32_t  fs_cpg;                        /* cylinders per group */
           int32_t  fs_ipg;                        /* inodes per group */
           int32_t  fs_fpg;                        /* blocks per group * fs_frag */
   /* this data must be re-computed after crashes */
           struct  csum fs_cstotal;        /* cylinder summary information */
   /* these fields are cleared at mount time */
           int8_t   fs_fmod;               /* super block modified flag */
           int8_t   fs_clean;              /* file system is clean flag */
           int8_t   fs_ronly;              /* mounted read-only flag */
           int8_t   fs_flags;              /* currently unused flag */
           u_char   fs_fsmnt[MAXMNTLEN];   /* name mounted on */
   /* these fields retain the current block allocation info */
           int32_t  fs_cgrotor;            /* last cg searched */
           void    *fs_ocsp[NOCSPTRS];     /* list of fs_cs info buffers */
           u_int8_t *fs_contigdirs;        /* # of contiguously allocated dirs */
           struct  csum *fs_csp;           /* list of fs_cs info buffers */
           int32_t  *fs_maxcluster;        /* max cluster in each cyl group */
           int32_t  fs_cpc;                /* cyl per cycle in postbl */
           int16_t  fs_opostbl[16][8];     /* old rotation block list head */
           int32_t  fs_avgfilesize;        /* expected average file size */
           int32_t  fs_avgfpdir;           /* expected # of files per directory */
           int32_t  fs_sparecon[48];       /* reserved for future constants */
           int32_t  fs_contigsumsize;      /* size of cluster summary array */ 
           int32_t  fs_maxsymlinklen;      /* max length of an internal symlink */
           int32_t  fs_inodefmt;           /* format of on-disk inodes */
           u_int64_t fs_maxfilesize;       /* maximum representable file size */
           int64_t  fs_qbmask;             /* ~fs_bmask for use with 64-bit size */
           int64_t  fs_qfmask;             /* ~fs_fmask for use with 64-bit size */
           int32_t  fs_state;              /* validate fs_clean field */
           int32_t  fs_postblformat;       /* format of positional layout tables */
           int32_t  fs_nrpos;              /* number of rotational positions */
           int32_t  fs_postbloff;          /* (u_int16) rotation block list head */
           int32_t  fs_rotbloff;           /* (u_int8) blocks for each rotation */
           int32_t  fs_magic;              /* magic number */
           u_int8_t fs_space[1];           /* list of blocks for each rotation */
   /* actually longer */
   };
   
   /*
    * Filesystem identification
    */
   #define FS_MAGIC        0x011954        /* the fast filesystem magic number */
   #define FS_OKAY         0x7c269d38      /* superblock checksum */
   #define FS_42INODEFMT   -1              /* 4.2BSD inode format */
   #define FS_44INODEFMT   2               /* 4.4BSD inode format */
   /*
    * Preference for optimization.
    */
   #define FS_OPTTIME      0       /* minimize allocation time */
   #define FS_OPTSPACE     1       /* minimize disk fragmentation */
   
   /*
    * Rotational layout table format types
    */
   #define FS_42POSTBLFMT          -1      /* 4.2BSD rotational table format */
   #define FS_DYNAMICPOSTBLFMT     1       /* dynamic rotational table format */
   /*
    * Macros for access to superblock array structures
    */
   #define fs_postbl(fs, cylno) \
       (((fs)->fs_postblformat == FS_42POSTBLFMT) \
       ? ((fs)->fs_opostbl[cylno]) \
       : ((int16_t *)((u_int8_t *)(fs) + \
           (fs)->fs_postbloff) + (cylno) * (fs)->fs_nrpos))
   #define fs_rotbl(fs) \
       (((fs)->fs_postblformat == FS_42POSTBLFMT) \
       ? ((fs)->fs_space) \
       : ((u_int8_t *)((u_int8_t *)(fs) + (fs)->fs_rotbloff)))
   
   /*
    * The size of a cylinder group is calculated by CGSIZE. The maximum size
    * is limited by the fact that cylinder groups are at most one block.
    * Its size is derived from the size of the maps maintained in the 
    * cylinder group and the (struct cg) size.
    */
   #define CGSIZE(fs) \
       /* base cg */       (sizeof(struct cg) + sizeof(int32_t) + \
       /* blktot size */   (fs)->fs_cpg * sizeof(int32_t) + \
       /* blks size */     (fs)->fs_cpg * (fs)->fs_nrpos * sizeof(int16_t) + \
       /* inode map */     howmany((fs)->fs_ipg, NBBY) + \
       /* block map */     howmany((fs)->fs_cpg * (fs)->fs_spc / NSPF(fs), NBBY) +\
       /* if present */    ((fs)->fs_contigsumsize <= 0 ? 0 : \
       /* cluster sum */   (fs)->fs_contigsumsize * sizeof(int32_t) + \
       /* cluster map */   howmany((fs)->fs_cpg * (fs)->fs_spc / NSPB(fs), NBBY)))
   
   /*
    * Convert cylinder group to base address of its global summary info.
    *
    * N.B. This macro assumes that sizeof(struct csum) is a power of two.
    */
   #define fs_cs(fs, indx) fs_csp[indx]
   
   /*
    * Cylinder group block for a file system.
    */
   #define CG_MAGIC        0x090255
   struct cg {
           int32_t  cg_firstfield;         /* historic cyl groups linked list */
           int32_t  cg_magic;              /* magic number */
           time_t   cg_time;               /* time last written */
           int32_t  cg_cgx;                /* we are the cgx'th cylinder group */
           int16_t  cg_ncyl;               /* number of cyl's this cg */
           int16_t  cg_niblk;              /* number of inode blocks this cg */
           int32_t  cg_ndblk;              /* number of data blocks this cg */
           struct  csum cg_cs;             /* cylinder summary information */
           int32_t  cg_rotor;              /* position of last used block */
           int32_t  cg_frotor;             /* position of last used frag */
           int32_t  cg_irotor;             /* position of last used inode */
           int32_t  cg_frsum[MAXFRAG];     /* counts of available frags */
           int32_t  cg_btotoff;            /* (int32) block totals per cylinder */
           int32_t  cg_boff;               /* (u_int16) free block positions */
           int32_t  cg_iusedoff;           /* (u_int8) used inode map */
           int32_t  cg_freeoff;            /* (u_int8) free block map */
           int32_t  cg_nextfreeoff;        /* (u_int8) next available space */
           int32_t  cg_clustersumoff;      /* (u_int32) counts of avail clusters */
           int32_t  cg_clusteroff;         /* (u_int8) free cluster map */
           int32_t  cg_nclusterblks;       /* number of clusters this cg */
           int32_t  cg_sparecon[13];       /* reserved for future use */
           u_int8_t cg_space[1];           /* space for cylinder group maps */
   /* actually longer */
   };
   
   /*
    * Macros for access to cylinder group array structures
    */
   #define cg_blktot(cgp) \
       (((cgp)->cg_magic != CG_MAGIC) \
       ? (((struct ocg *)(cgp))->cg_btot) \
       : ((int32_t *)((u_int8_t *)(cgp) + (cgp)->cg_btotoff)))
   #define cg_blks(fs, cgp, cylno) \
       (((cgp)->cg_magic != CG_MAGIC) \
       ? (((struct ocg *)(cgp))->cg_b[cylno]) \
       : ((int16_t *)((u_int8_t *)(cgp) + \
           (cgp)->cg_boff) + (cylno) * (fs)->fs_nrpos))
   #define cg_inosused(cgp) \
       (((cgp)->cg_magic != CG_MAGIC) \
       ? (((struct ocg *)(cgp))->cg_iused) \
       : ((u_int8_t *)((u_int8_t *)(cgp) + (cgp)->cg_iusedoff)))
   #define cg_blksfree(cgp) \
       (((cgp)->cg_magic != CG_MAGIC) \
       ? (((struct ocg *)(cgp))->cg_free) \
       : ((u_int8_t *)((u_int8_t *)(cgp) + (cgp)->cg_freeoff)))
   #define cg_chkmagic(cgp) \
       ((cgp)->cg_magic == CG_MAGIC || ((struct ocg *)(cgp))->cg_magic == CG_MAGIC)
   #define cg_clustersfree(cgp) \
       ((u_int8_t *)((u_int8_t *)(cgp) + (cgp)->cg_clusteroff))
   #define cg_clustersum(cgp) \
       ((int32_t *)((u_int8_t *)(cgp) + (cgp)->cg_clustersumoff))
   
   /*
    * The following structure is defined
    * for compatibility with old file systems.
    */
   struct ocg {
           int32_t  cg_firstfield;         /* historic linked list of cyl groups */
           int32_t  cg_unused_1;           /*     used for incore cyl groups */
           time_t   cg_time;               /* time last written */
           int32_t  cg_cgx;                /* we are the cgx'th cylinder group */
           int16_t  cg_ncyl;               /* number of cyl's this cg */
           int16_t  cg_niblk;              /* number of inode blocks this cg */
           int32_t  cg_ndblk;              /* number of data blocks this cg */
           struct  csum cg_cs;             /* cylinder summary information */
           int32_t  cg_rotor;              /* position of last used block */
           int32_t  cg_frotor;             /* position of last used frag */
           int32_t  cg_irotor;             /* position of last used inode */
           int32_t  cg_frsum[8];           /* counts of available frags */
           int32_t  cg_btot[32];           /* block totals per cylinder */
           int16_t  cg_b[32][8];           /* positions of free blocks */
           u_int8_t cg_iused[256];         /* used inode map */
           int32_t  cg_magic;              /* magic number */
           u_int8_t cg_free[1];            /* free block map */
   /* actually longer */
   };
   
   /*
    * Turn file system block numbers into disk block addresses.
    * This maps file system blocks to device size blocks.
    */
   #define fsbtodb(fs, b)  ((b) << (fs)->fs_fsbtodb)
   #define dbtofsb(fs, b)  ((b) >> (fs)->fs_fsbtodb)
   
   /*
    * Cylinder group macros to locate things in cylinder groups.
    * They calc file system addresses of cylinder group data structures.
    */
   #define cgbase(fs, c)   ((ufs_daddr_t)((fs)->fs_fpg * (c)))
   #define cgdmin(fs, c)   (cgstart(fs, c) + (fs)->fs_dblkno)      /* 1st data */
   #define cgimin(fs, c)   (cgstart(fs, c) + (fs)->fs_iblkno)      /* inode blk */
   #define cgsblock(fs, c) (cgstart(fs, c) + (fs)->fs_sblkno)      /* super blk */
   #define cgtod(fs, c)    (cgstart(fs, c) + (fs)->fs_cblkno)      /* cg block */
   #define cgstart(fs, c)                                                  \
           (cgbase(fs, c) + (fs)->fs_cgoffset * ((c) & ~((fs)->fs_cgmask)))
   
   /*
    * Macros for handling inode numbers:
    *     inode number to file system block offset.
    *     inode number to cylinder group number.
    *     inode number to file system block address.
    */
   #define ino_to_cg(fs, x)        ((x) / (fs)->fs_ipg)
   #define ino_to_fsba(fs, x)                                              \
           ((ufs_daddr_t)(cgimin(fs, ino_to_cg(fs, x)) +                   \
               (blkstofrags((fs), (((x) % (fs)->fs_ipg) / INOPB(fs))))))
   #define ino_to_fsbo(fs, x)      ((x) % INOPB(fs))
   
   /*
    * Give cylinder group number for a file system block.
    * Give cylinder group block number for a file system block.
    */
   #define dtog(fs, d)     ((d) / (fs)->fs_fpg)
   #define dtogd(fs, d)    ((d) % (fs)->fs_fpg)
   
   /*
    * Extract the bits for a block from a map.
    * Compute the cylinder and rotational position of a cyl block addr.
    */
   #define blkmap(fs, map, loc) \
       (((map)[(loc) / NBBY] >> ((loc) % NBBY)) & (0xff >> (NBBY - (fs)->fs_frag)))
   #define cbtocylno(fs, bno) \
       ((bno) * NSPF(fs) / (fs)->fs_spc)
   #define cbtorpos(fs, bno) \
       (((bno) * NSPF(fs) % (fs)->fs_spc / (fs)->fs_nsect * (fs)->fs_trackskew + \
        (bno) * NSPF(fs) % (fs)->fs_spc % (fs)->fs_nsect * (fs)->fs_interleave) % \
        (fs)->fs_nsect * (fs)->fs_nrpos / (fs)->fs_npsect)
   
   /*
    * The following macros optimize certain frequently calculated
    * quantities by using shifts and masks in place of divisions
    * modulos and multiplications.
    */
   #define blkoff(fs, loc)         /* calculates (loc % fs->fs_bsize) */ \
           ((loc) & (fs)->fs_qbmask)
   #define fragoff(fs, loc)        /* calculates (loc % fs->fs_fsize) */ \
           ((loc) & (fs)->fs_qfmask)
   #define lblktosize(fs, blk)     /* calculates (blk * fs->fs_bsize) */ \
           ((blk) << (fs)->fs_bshift)
   #define lblkno(fs, loc)         /* calculates (loc / fs->fs_bsize) */ \
           ((loc) >> (fs)->fs_bshift)
   #define numfrags(fs, loc)       /* calculates (loc / fs->fs_fsize) */ \
           ((loc) >> (fs)->fs_fshift)
   #define blkroundup(fs, size)    /* calculates roundup(size, fs->fs_bsize) */ \
           (((size) + (fs)->fs_qbmask) & (fs)->fs_bmask)
   #define fragroundup(fs, size)   /* calculates roundup(size, fs->fs_fsize) */ \
           (((size) + (fs)->fs_qfmask) & (fs)->fs_fmask)
   #define fragstoblks(fs, frags)  /* calculates (frags / fs->fs_frag) */ \
           ((frags) >> (fs)->fs_fragshift)
   #define blkstofrags(fs, blks)   /* calculates (blks * fs->fs_frag) */ \
           ((blks) << (fs)->fs_fragshift)
   #define fragnum(fs, fsb)        /* calculates (fsb % fs->fs_frag) */ \
           ((fsb) & ((fs)->fs_frag - 1))
   #define blknum(fs, fsb)         /* calculates rounddown(fsb, fs->fs_frag) */ \
           ((fsb) &~ ((fs)->fs_frag - 1))
   
   /*
    * Determine the number of available frags given a
    * percentage to hold in reserve.
    */
   #define freespace(fs, percentreserved) \
           (blkstofrags((fs), (fs)->fs_cstotal.cs_nbfree) + \
           (fs)->fs_cstotal.cs_nffree - ((fs)->fs_dsize * (percentreserved) / 100))
   
   /*
    * Determining the size of a file block in the file system.
    */
   #define blksize(fs, ip, lbn) \
           (((lbn) >= NDADDR || (ip)->i_size >= ((lbn) + 1) << (fs)->fs_bshift) \
               ? (fs)->fs_bsize \
               : (fragroundup(fs, blkoff(fs, (ip)->i_size))))
   #define dblksize(fs, dip, lbn) \
           (((lbn) >= NDADDR || (dip)->di_size >= ((lbn) + 1) << (fs)->fs_bshift) \
               ? (fs)->fs_bsize \
               : (fragroundup(fs, blkoff(fs, (dip)->di_size))))
   
   /*
    * Number of disk sectors per block/fragment; assumes DEV_BSIZE byte
    * sector size.
    */
   #define NSPB(fs)        ((fs)->fs_nspf << (fs)->fs_fragshift)
   #define NSPF(fs)        ((fs)->fs_nspf)
   
   /*
    * Number of inodes in a secondary storage block/fragment.
    */
   #define INOPB(fs)       ((fs)->fs_inopb)
   #define INOPF(fs)       ((fs)->fs_inopb >> (fs)->fs_fragshift)
   
   /*
    * Number of indirects in a file system block.
    */
   #define NINDIR(fs)      ((fs)->fs_nindir)
   
   /*
    * This macro controls whether the file system format is byte swapped or not.
    * At NeXT, all little endian machines read and write big endian file systems.
    */
   #define BIG_ENDIAN_FS   (__LITTLE_ENDIAN__)
   
   #ifdef __APPLE_API_PRIVATE
   extern int inside[], around[];
   extern u_char *fragtbl[];
   #endif /* __APPLE_API_PRIVATE */
   
   
   /*
    * UFS Label:
    *   The purpose of this label is to name a UFS/FFS filesystem.  The label
    *   is located at offset 7K (BBSIZE=8K - UFS_LABEL_SIZE=1K = 7K) of the 
    *   partition.  The first 7K is still available for boot blocks.
    */
   
   #define UFS_LABEL_MAGIC         { 'L', 'A', 'B', 'L' }
   #define UFS_LABEL_SIZE          1024
   #define UFS_LABEL_OFFSET        (BBSIZE - UFS_LABEL_SIZE) /* top 1K */
   #define UFS_LABEL_VERSION       1
   #define UFS_MAX_LABEL_NAME      512
   
   struct ufslabel {
       u_int32_t           ul_magic;
       u_int16_t           ul_checksum;    /* checksum over entire label*/
       u_int32_t           ul_version;     /* label version */
       u_int32_t           ul_time;        /* creation time */
       u_int16_t           ul_namelen;     /* filesystem name length */
       u_char              ul_name[UFS_MAX_LABEL_NAME]; /* filesystem name */
       u_int64_t           ul_uuid;        /* filesystem uuid */
       u_char              ul_reserved[24];/* reserved for future use */
       u_char              ul_unused[460]; /* pad out to 1K */
   };
   
   #endif /* __APPLE_API_UNSTABLE */
   #endif /* ! _FFS_FS_H_ */

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