FreeBSD/Linux Kernel Cross Reference
sys/fs/ext2fs/fs.h

     /*-
      *  modified for EXT2FS support in Lites 1.1
      *
      *  Aug 1995, Godmar Back (gback@cs.utah.edu)
      *  University of Utah, Department of Computer Science
      */
     /*-
      * 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.
     * 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        8.7 (Berkeley) 4/19/94
     * $FreeBSD$
     */
    
    #ifndef _FS_EXT2FS_FS_H_
    #define _FS_EXT2FS_FS_H_
    
    /*
     * 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.
     *
     * 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 SBSIZE          1024
    #define SBLOCK          2
    
    /*
     * 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
    
    /*
     * 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.
     *
     * XXX:FS_MAXCONTIG is set to 16 to conserve space. Here we set
     * EXT2_MAXCONTIG to 32 for better performance.
     */
    #define EXT2_MAXCONTIG  32
    
    /*
     * 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.
     * AVFPDIR is the expected number of files per directory. AVGDIRSIZE is
     * obtained by multiplying AVFPDIR and AVFILESIZ which is assumed to be
     * 16384.
     */
    
    #define AFPDIR          64
    #define AVGDIRSIZE      1048576
    
    /*
     * Macros for access to superblock array structures
     */
    
    /*
     * Turn file system block numbers into disk block addresses.
     * This maps file system blocks to device size blocks.
    */
   #define fsbtodb(fs, b)  ((daddr_t)(b) << (fs)->e2fs_fsbtodb)
   #define dbtofsb(fs, b)  ((b) >> (fs)->e2fs_fsbtodb)
   
   /* get group containing inode */
   #define ino_to_cg(fs, x)        (((x) - 1) / (fs->e2fs_ipg))
   
   /* get block containing inode from its number x */
   #define ino_to_fsba(fs, x)                                              \
           ((fs)->e2fs_gd[ino_to_cg((fs), (x))].ext2bgd_i_tables +         \
           (((x) - 1) % (fs)->e2fs->e2fs_ipg) / (fs)->e2fs_ipb)
   
   /* get offset for inode in block */
   #define ino_to_fsbo(fs, x)      ((x-1) % (fs->e2fs_ipb))
   
   /*
    * 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->e2fs->e2fs_first_dblock) / \
                           EXT2_BLOCKS_PER_GROUP(fs))
   #define dtogd(fs, d)    (((d) - fs->e2fs->e2fs_first_dblock) % \
                           EXT2_BLOCKS_PER_GROUP(fs))
   
   /*
    * 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)->e2fs_qbmask)
   
   #define lblktosize(fs, blk)     /* calculates (blk * fs->fs_bsize) */ \
           ((blk) << (fs->e2fs_bshift))
   
   #define lblkno(fs, loc)         /* calculates (loc / fs->fs_bsize) */ \
           ((loc) >> (fs->e2fs_bshift))
   
   /* no fragments -> logical block number equal # of frags */
   #define numfrags(fs, loc)       /* calculates (loc / fs->fs_fsize) */ \
           ((loc) >> (fs->e2fs_bshift))
   
   #define fragroundup(fs, size)   /* calculates roundup(size, fs->fs_fsize) */ \
           roundup(size, fs->e2fs_fsize)
           /* was (((size) + (fs)->fs_qfmask) & (fs)->fs_fmask) */
   
   /*
    * Determining the size of a file block in the file system.
    * easy w/o fragments
    */
   #define blksize(fs, ip, lbn) ((fs)->e2fs_fsize)
   
   /*
    * INOPB is the number of inodes in a secondary storage block.
    */
   #define INOPB(fs)       (fs->e2fs_ipb)
   
   /*
    * NINDIR is the number of indirects in a file system block.
    */
   #define NINDIR(fs)      (EXT2_ADDR_PER_BLOCK(fs))
   
   #endif  /* !_FS_EXT2FS_FS_H_ */

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