Final Year Project: Using Linux Filesystems Under Windows   Chris Bryden BEng. Electronics and Software Engineering    School of Computer Science   University of Birmingham 13 · =s_log_frag_size - This is used to calculate the fragment size (in bytes). The actual  fragment  size  is  given  by:  1024  <<  s_log  frag_size  if  s_log_frag _size   is   positive   and   1024   >>   -s_log_frag_size   if   s_log_frag_size   is negative. · =s_blocks_per_group - The total number of blocks per group. · =s_frags_per_group - The total number of fragments per group. · =s_mtime - The time when the filesystem was last mounted. · =s_wtime - The time when the superblock was last written. · =s_mnt_count - The number of times the filesystem has been mounted in read- write mode without being checked. · =s_max_mnt_count -  The  number  of  times  the  filesystem  can  be  mounted  in read-write mode before a check is forced. · =s_magic - The superblock magic number, used for identification purposes. For a  normal  ext2  filesystem  the  magic  number  is  0xEF53,  on  older  filesystems (prior to version 0.2b) it is 0xEF51. · =s_state - The current state of the filesystem, it contains either of two values: EXT2_VALID_FS (0x0001) for a clean filesystem, or EXT2_ERROR_FS (0x0002) for a filesystem that was not unmounted cleanly. · =s_errors - Indicates which operation to perform when errors are detected. · =s_pad - Unused padding. · =s_lastcheck - The time when the last check was made on the filesystem. · =s_checkinterval -   The   maximum   possible   time   between   checks   on   the filesystem. · =s_reserved - Unused. All times are measured in seconds since 00:00:00 GMT, January 1^st 1970. On mounting a filesystem, the first operation is to read the superblock and perform  checks  for  the  validity  of  the  filesystem.  As  can  be  seen  from  the descriptions  above,  the  superblock  contains  information  that  is  fundamental  to the operation of the filesystem, it is for this reason that spare copies are made at the beginning of each block group.