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  * SPDX-License-Identifier: BSD-3-Clause
    9  *
   10  * Copyright (c) 1982, 1986, 1993
   11  *      The Regents of the University of California.  All rights reserved.
   12  *
   13  * Redistribution and use in source and binary forms, with or without
   14  * modification, are permitted provided that the following conditions
   15  * are met:
   16  * 1. Redistributions of source code must retain the above copyright
   17  *    notice, this list of conditions and the following disclaimer.
   18  * 2. Redistributions in binary form must reproduce the above copyright
   19  *    notice, this list of conditions and the following disclaimer in the
   20  *    documentation and/or other materials provided with the distribution.
   21  * 3. Neither the name of the University nor the names of its contributors
   22  *    may be used to endorse or promote products derived from this software
   23  *    without specific prior written permission.
   24  *
   25  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   26  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   27  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   28  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   29  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   30  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   31  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   32  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   33  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   34  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   35  * SUCH DAMAGE.
   36  *
   37  *      @(#)fs.h        8.7 (Berkeley) 4/19/94
   38  * $FreeBSD: head/sys/fs/ext2fs/fs.h 346267 2019-04-16 11:20:10Z fsu $
   39  */
   40 
   41 #ifndef _FS_EXT2FS_FS_H_
   42 #define _FS_EXT2FS_FS_H_
   43 
   44 /*
   45  * Each disk drive contains some number of file systems.
   46  * A file system consists of a number of cylinder groups.
   47  * Each cylinder group has inodes and data.
   48  *
   49  * A file system is described by its super-block, which in turn
   50  * describes the cylinder groups.  The super-block is critical
   51  * data and is replicated in each cylinder group to protect against
   52  * catastrophic loss.  This is done at `newfs' time and the critical
   53  * super-block data does not change, so the copies need not be
   54  * referenced further unless disaster strikes.
   55  *
   56  * The first boot and super blocks are given in absolute disk addresses.
   57  * The byte-offset forms are preferred, as they don't imply a sector size.
   58  */
   59 #define SBSIZE          1024
   60 #define SBLOCK          2
   61 
   62 /*
   63  * The path name on which the file system is mounted is maintained
   64  * in fs_fsmnt. MAXMNTLEN defines the amount of space allocated in
   65  * the super block for this name.
   66  */
   67 #define MAXMNTLEN       512
   68 
   69 /*
   70  * A summary of contiguous blocks of various sizes is maintained
   71  * in each cylinder group. Normally this is set by the initial
   72  * value of fs_maxcontig.
   73  *
   74  * XXX:FS_MAXCONTIG is set to 16 to conserve space. Here we set
   75  * EXT2_MAXCONTIG to 32 for better performance.
   76  */
   77 #define EXT2_MAXCONTIG  32
   78 
   79 /*
   80  * Grigoriy Orlov <gluk@ptci.ru> has done some extensive work to fine
   81  * tune the layout preferences for directories within a filesystem.
   82  * His algorithm can be tuned by adjusting the following parameters
   83  * which tell the system the average file size and the average number
   84  * of files per directory. These defaults are well selected for typical
   85  * filesystems, but may need to be tuned for odd cases like filesystems
   86  * being used for squid caches or news spools.
   87  * AVFPDIR is the expected number of files per directory. AVGDIRSIZE is
   88  * obtained by multiplying AVFPDIR and AVFILESIZ which is assumed to be
   89  * 16384.
   90  */
   91 
   92 #define AFPDIR          64
   93 #define AVGDIRSIZE      1048576
   94 
   95 /*
   96  * Macros for access to superblock array structures
   97  */
   98 
   99 /*
  100  * Turn file system block numbers into disk block addresses.
  101  * This maps file system blocks to device size blocks.
  102  */
  103 #define fsbtodb(fs, b)  ((daddr_t)(b) << (fs)->e2fs_fsbtodb)
  104 #define dbtofsb(fs, b)  ((b) >> (fs)->e2fs_fsbtodb)
  105 
  106 /* get group containing inode */
  107 #define ino_to_cg(fs, x)        (((x) - 1) / (fs->e2fs_ipg))
  108 
  109 /* get block containing inode from its number x */
  110 #define ino_to_fsba(fs, x)                                              \
  111         (e2fs_gd_get_i_tables(&(fs)->e2fs_gd[ino_to_cg((fs), (x))]) +   \
  112         (((x) - 1) % (fs)->e2fs->e2fs_ipg) / (fs)->e2fs_ipb)
  113 
  114 /* get offset for inode in block */
  115 #define ino_to_fsbo(fs, x)      ((x-1) % (fs->e2fs_ipb))
  116 
  117 /*
  118  * Give cylinder group number for a file system block.
  119  * Give cylinder group block number for a file system block.
  120  */
  121 #define dtog(fs, d)     (((d) - fs->e2fs->e2fs_first_dblock) / \
  122                         EXT2_BLOCKS_PER_GROUP(fs))
  123 #define dtogd(fs, d)    (((d) - fs->e2fs->e2fs_first_dblock) % \
  124                         EXT2_BLOCKS_PER_GROUP(fs))
  125 
  126 /*
  127  * The following macros optimize certain frequently calculated
  128  * quantities by using shifts and masks in place of divisions
  129  * modulos and multiplications.
  130  */
  131 #define blkoff(fs, loc)         /* calculates (loc % fs->fs_bsize) */ \
  132         ((loc) & (fs)->e2fs_qbmask)
  133 
  134 #define lblktosize(fs, blk)     /* calculates (blk * fs->fs_bsize) */ \
  135         ((blk) << (fs->e2fs_bshift))
  136 
  137 #define lblkno(fs, loc)         /* calculates (loc / fs->fs_bsize) */ \
  138         ((loc) >> (fs->e2fs_bshift))
  139 
  140 /* no fragments -> logical block number equal # of frags */
  141 #define numfrags(fs, loc)       /* calculates (loc / fs->fs_fsize) */ \
  142         ((loc) >> (fs->e2fs_bshift))
  143 
  144 #define fragroundup(fs, size)   /* calculates roundup(size, fs->fs_fsize) */ \
  145         roundup(size, fs->e2fs_fsize)
  146         /* was (((size) + (fs)->fs_qfmask) & (fs)->fs_fmask) */
  147 
  148 /*
  149  * Determining the size of a file block in the file system.
  150  * easy w/o fragments
  151  */
  152 #define blksize(fs, ip, lbn) ((fs)->e2fs_fsize)
  153 
  154 /*
  155  * INOPB is the number of inodes in a secondary storage block.
  156  */
  157 #define INOPB(fs)       (fs->e2fs_ipb)
  158 
  159 /*
  160  * NINDIR is the number of indirects in a file system block.
  161  */
  162 #define NINDIR(fs)      (EXT2_ADDR_PER_BLOCK(fs))
  163 
  164 /*
  165  * Use if additional debug logging is required.
  166  */
  167 /* #define EXT2FS_PRINT_EXTENTS */
  168 
  169 #endif  /* !_FS_EXT2FS_FS_H_ */

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