filsys.h file

/* The following disk-blocks are formatted or reserved:
 * 
 *      ipl block 0 - not changed by filesystem.
 *
 *      superblocks at  1 x 4096 (primary superblock) and  31 x
 *      4096 (secondary superblock). the secondary super-block  
 *      location is likely to be on a different disk-surface than
 *      the primary super-block. both structures are allocated as
 *      fragments in ".superblock".
 *
 *      fragments for .inodes according to BSD layout. each 
 *      allocation group contains a fixed number of disk inodes. 
 *      for fsv3 file systems, each allocation group contains one
 *      inode per 4096 byte fragment of the allocation group, 
 *      with the number of fragments within each group described
 *      by the s_agsize field of the superblock. for fsv3p file 
 *      systems, the number of inodes per group is described by 
 *      the s_iagsize field of the superblock and may be less 
 *      than or greater than the number of fragments per group. 
 *      for these file systems, s_agsize describes the number of   
 *      s_fragsize fragments contained within each allocation 
 *      group. 
 *
 *      the first allocation group inodes starts at 32 x
 *      4096 bytes and consumes consecutive fragments sufficient
 *      to hold the group's inodes. the inode fragments for all
 *      other allocation groups start in the first fragments of 
 *      the allocation group and continue in consecutive 
 *      fragments sufficient to hold the group's inodes. 
 *
 *      other fragments are allocated for .indirect, .diskmap, 
 *      .inodemap, and their indirect blocks starting in the 
 *      first allocation-group.
 *
 * The special fs inodes formatted and their usage is as follows:
 *
 *      inode 0 - never allocated - reserved by setting 
 *      n_link = 1
 *      inode 1 - inode for .superblock
 *      inode 2 - inode for root directory
 *      inode 3 - inode for .inodes
 *      inode 4 - inode for .indirect
 *      inode 5 - inode for .inodemap - allocation map for 
 *      .inodes
 *      inode 6 - inode for .diskmap - disk allocation map
 *      inode 7 - inode for .inodex - inode extensions
 *      inode 8 - inode for .inodexmap - allocation map for 
 *      .inodex
 *      inode 9 - 16 - reserved for future extensions
 *
 * except for the root directory, the special inodes are not in 
 * any directory.
 *
 */

#define 
IPL_B            0
#define SUPER_B 1
#define SUPER_B1         31
#define INODES_B         32
#define NON_B            0
#define SUPER_I 1
#define ROOTDIR_I        2
#define INODES_I         3
#define INDIR_I 4
#define INOMAP_I         5
#define DISKMAP_I        6
#define INODEX_I         7
#define INDOESMAP_I      8

/*
 * super block format. primary superblock is located in the 
 * second 4096 bytes of the file system. 
 * the secondary super-block is not used except for disaster 
 * recovery.
*/
 struct superblock
 {
   char s_magic[4];     /* magic number */
   char s_flag[4];      /* flag word (see below) */
   int  s_agsize;       /* fragments per allocation group */     
   int  s_logserial;  /* serial number of log when fs mounted */
   daddr_t s_fsize;     /* size (in 512 bytes) of entire fs */
   short s_bsize;       /* block size (in bytes) for this 
                
           system */
   short s_spare;       /* unused.                      */
   char  s_fname[6];  /* name of this file system        */
   char  s_fpack[6];  /* name of this volume             */
   dev_t s_logdev;      /* device address of log        */
  
  /* current file system state information, values change over 
time */
 char   s_fmod;    /* flag: set when file system is mounted */
 char   s_ronly;   /*flag: file system is read only */
 time_t   s_time;    /* time of last superblock update      */
 
  /* more persistent 
information              &
nbsp;               &
nbsp;*/
  int s_version;    /* version 
number               
           */
  int s_fragsize;    /* fragment size in bytes (fsv3p only)    */
  int s_iagsize;     /* disk inodes per alloc grp (fsv3p only) */
  int s_compress;    /* > 0 if data compression                */

};
  
    /* Version 4 fs magic number  */
    #define fsv4magic  "\102\041\207\145"  
    /* Version 4p fs magic number */
    #define fsv4pmagic "\145\207\041\102"  
    /* Version 4p version number  */
    #define fsv4pvers  1

if (strncmp(sp->s_magic,fsv3magic,4) == 0)

if (strncmp(sp->s_magic,fsv3pmagic,4) == 0 &&
    sp->s_version == fsv3pvers)