The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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

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    1 /*-
    2  *  modified for EXT2FS support in Lites 1.1
    3  *
    4  *  Aug 1995, Godmar Back (gback@cs.utah.edu)
    5  *  University of Utah, Department of Computer Science
    6  */
    7 /*-
    8  * Copyright (c) 1982, 1986, 1993
    9  *      The Regents of the University of California.  All rights reserved.
   10  *
   11  * Redistribution and use in source and binary forms, with or without
   12  * modification, are permitted provided that the following conditions
   13  * are met:
   14  * 1. Redistributions of source code must retain the above copyright
   15  *    notice, this list of conditions and the following disclaimer.
   16  * 2. Redistributions in binary form must reproduce the above copyright
   17  *    notice, this list of conditions and the following disclaimer in the
   18  *    documentation and/or other materials provided with the distribution.
   19  * 4. Neither the name of the University nor the names of its contributors
   20  *    may be used to endorse or promote products derived from this software
   21  *    without specific prior written permission.
   22  *
   23  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   24  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   25  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   26  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   27  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   28  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   29  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   30  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   31  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   32  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   33  * SUCH DAMAGE.
   34  *
   35  *      @(#)fs.h        8.7 (Berkeley) 4/19/94
   36  * $FreeBSD: releng/9.2/sys/fs/ext2fs/fs.h 252234 2013-06-26 04:34:16Z pfg $
   37  */
   38 
   39 #ifndef _FS_EXT2FS_FS_H_
   40 #define _FS_EXT2FS_FS_H_
   41 
   42 /*
   43  * Each disk drive contains some number of file systems.
   44  * A file system consists of a number of cylinder groups.
   45  * Each cylinder group has inodes and data.
   46  *
   47  * A file system is described by its super-block, which in turn
   48  * describes the cylinder groups.  The super-block is critical
   49  * data and is replicated in each cylinder group to protect against
   50  * catastrophic loss.  This is done at `newfs' time and the critical
   51  * super-block data does not change, so the copies need not be
   52  * referenced further unless disaster strikes.
   53  *
   54  * The first boot and super blocks are given in absolute disk addresses.
   55  * The byte-offset forms are preferred, as they don't imply a sector size.
   56  */
   57 #define SBSIZE          1024
   58 #define SBLOCK          2
   59 
   60 /*
   61  * The path name on which the file system is mounted is maintained
   62  * in fs_fsmnt. MAXMNTLEN defines the amount of space allocated in 
   63  * the super block for this name. 
   64  */
   65 #define MAXMNTLEN       512
   66 
   67 /*
   68  * A summary of contiguous blocks of various sizes is maintained
   69  * in each cylinder group. Normally this is set by the initial
   70  * value of fs_maxcontig.
   71  *
   72  * XXX:FS_MAXCONTIG is set to 16 to conserve space. Here we set
   73  * EXT2_MAXCONTIG to 32 for better performance.
   74  */
   75 #define EXT2_MAXCONTIG  32
   76 
   77 /*
   78  * Grigoriy Orlov <gluk@ptci.ru> has done some extensive work to fine
   79  * tune the layout preferences for directories within a filesystem.
   80  * His algorithm can be tuned by adjusting the following parameters
   81  * which tell the system the average file size and the average number
   82  * of files per directory. These defaults are well selected for typical
   83  * filesystems, but may need to be tuned for odd cases like filesystems
   84  * being used for squid caches or news spools.
   85  * AVFPDIR is the expected number of files per directory. AVGDIRSIZE is 
   86  * obtained by multiplying AVFPDIR and AVFILESIZ which is assumed to be 
   87  * 16384.
   88  */
   89 
   90 #define AFPDIR          64
   91 #define AVGDIRSIZE      1048576
   92 
   93 /*
   94  * Macros for access to superblock array structures
   95  */
   96 
   97 /*
   98  * Turn file system block numbers into disk block addresses.
   99  * This maps file system blocks to device size blocks.
  100  */
  101 #define fsbtodb(fs, b)  ((daddr_t)(b) << (fs)->e2fs_fsbtodb)
  102 #define dbtofsb(fs, b)  ((b) >> (fs)->e2fs_fsbtodb)
  103 
  104 /* get group containing inode */
  105 #define ino_to_cg(fs, x)        (((x) - 1) / (fs->e2fs_ipg))
  106 
  107 /* get block containing inode from its number x */
  108 #define ino_to_fsba(fs, x)                                              \
  109         ((fs)->e2fs_gd[ino_to_cg((fs), (x))].ext2bgd_i_tables +         \
  110         (((x) - 1) % (fs)->e2fs->e2fs_ipg) / (fs)->e2fs_ipb)
  111 
  112 /* get offset for inode in block */
  113 #define ino_to_fsbo(fs, x)      ((x-1) % (fs->e2fs_ipb))
  114 
  115 /*
  116  * Give cylinder group number for a file system block.
  117  * Give cylinder group block number for a file system block.
  118  */
  119 #define dtog(fs, d)     (((d) - fs->e2fs->e2fs_first_dblock) / \
  120                         EXT2_BLOCKS_PER_GROUP(fs))
  121 #define dtogd(fs, d)    (((d) - fs->e2fs->e2fs_first_dblock) % \
  122                         EXT2_BLOCKS_PER_GROUP(fs))
  123 
  124 /*
  125  * The following macros optimize certain frequently calculated
  126  * quantities by using shifts and masks in place of divisions
  127  * modulos and multiplications.
  128  */
  129 #define blkoff(fs, loc)         /* calculates (loc % fs->fs_bsize) */ \
  130         ((loc) & (fs)->e2fs_qbmask)
  131 
  132 #define lblktosize(fs, blk)     /* calculates (blk * fs->fs_bsize) */ \
  133         ((blk) << (fs->e2fs_bshift))
  134 
  135 #define lblkno(fs, loc)         /* calculates (loc / fs->fs_bsize) */ \
  136         ((loc) >> (fs->e2fs_bshift))
  137 
  138 /* no fragments -> logical block number equal # of frags */
  139 #define numfrags(fs, loc)       /* calculates (loc / fs->fs_fsize) */ \
  140         ((loc) >> (fs->e2fs_bshift))
  141 
  142 #define fragroundup(fs, size)   /* calculates roundup(size, fs->fs_fsize) */ \
  143         roundup(size, fs->e2fs_fsize)
  144         /* was (((size) + (fs)->fs_qfmask) & (fs)->fs_fmask) */
  145 
  146 /*
  147  * Determining the size of a file block in the file system.
  148  * easy w/o fragments
  149  */
  150 #define blksize(fs, ip, lbn) ((fs)->e2fs_fsize)
  151 
  152 /*
  153  * INOPB is the number of inodes in a secondary storage block.
  154  */
  155 #define INOPB(fs)       (fs->e2fs_ipb)
  156 
  157 /*
  158  * NINDIR is the number of indirects in a file system block.
  159  */
  160 #define NINDIR(fs)      (EXT2_ADDR_PER_BLOCK(fs))
  161 
  162 #endif /* !_FS_EXT2FS_FS_H_ */

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