logo.gif (6996 bytes)

Block header

A Root block contains very important information about the structure of a SFS disk.   It has information on the location and size of the disk, the blocksize used, locations of various important blocks, version information and some filesystem specific settings.

A SFS disk has two Root blocks; one located at the start of the partition and one at the end.  On startup the filesystem will check both Roots to see if it is a valid SFS disk.  If either one is missing SFS can still continue (although at the moment it won't).

A Root block could be missing on purpose.  For example, if you extend the partition at the end (adding a few MB's) then SFS can detect this with the information stored in the Root block located at the beginning (since only the end-offset has changed).   Same goes for the other way around, as long as you don't change start and end point at the same time.

When a Root block is missing because the partition has been made a bit larger, then SFS will in the future be able to resize itself without re-formatting the disk.

Field Type Description
bheader struct fsBlockHeader Standard block header.
version UWORD The version of the filesystem block structure.  You can check this field to identify what version of the filesystem your dealing with it and to see if you can handle this structure correctly.  Don't try to interpret the disk's structure when this field contains an unknown version number!
sequencenumber UWORD Used to identify which Root block was written last in case the sequencenumber on both Root blocks don't match.
datecreated ULONG Creation date of this volume.  This is the date when the disk was last formatted and will never be changed.
bits UBYTE Various settings, see below.
pad1 UBYTE Reserved, leave zero.
pad2 UWORD Reserved, leave zero.
reserved1 ULONG[2] Reserved, leave zero.
firstbyteh ULONG High 32-bits of a 64-bit number.  This is the first byte of our partition relative to the start of the disk.
firstbyte ULONG Low 32-bits of a 64-bit number.
lastbyteh ULONG High 32-bits of a 64-bit number.  This is the last byte (exclusive) of our partition relative to the start of the disk.
lastbyte ULONG Low 32-bits of a 64-bit number.
totalblocks ULONG The total number of blocks this partition consists of.
blocksize ULONG The size of a block of this partition.
reserved2 ULONG[2] Reserved, leave zero.
reserved3 ULONG[8] Reserved, leave zero.
bitmapbase BLCK Block number of the start of the Bitmap.
adminspacecontainer BLCK Block number of the first AdminSpaceContainer.
rootobjectcontainer BLCK Block number of the ObjectContainer which contains the root of the disk (this is where the volume name is stored).
extentbnoderoot BLCK Block number of the root of the Extent B-Tree.
reserved4 ULONG[4] Reserved, leave zero.
struct fsRootBlock {
  struct fsBlockHeader bheader;
  UWORD version;
  UWORD sequencenumber;
  ULONG datecreated;
  UBYTE bits;
  UBYTE pad1;
  UWORD pad2;
  ULONG reserved1[2];
  ULONG firstbyteh;
  ULONG firstbyte;
  ULONG lastbyteh;
  ULONG lastbyte;
  BLCK  totalblocks;
  ULONG blocksize;
  ULONG reserved2[2];
  ULONG reserved3[8];
  BLCK  bitmapbase;
  BLCK  adminspacecontainer;
  BLCK  rootobjectcontainer;
  BLCK  extentbnoderoot;
  ULONG reserved4[4];

All rights reserved.
For comments, problems or questions regarding this page contact John Hendrikx.
Last updated: 17 oktober 1998.