[Unix-jun72] Anyone working on V1 mkfs?

Tim Newsham newsham at lava.net
Fri May 2 13:21:54 AEST 2008

> I gave up and decided to write mkfs from scratch :-)

I did a little more research on the disks, and added my notes
to the machine.txt file.  Included below.  Looks like we should
be able to craft a tape image with a list of files and use the
cold boot mechanism to initialize the rf0 disk (which has to be
the root fs).  We may still want an mkfs for initializing an
rf03 later.


    rf0 - 1024 blocks, always mounted, has root and swap.
          last 64 blocks (32kbyte) allocated to swap by u0.s
          u0.s can setup rudimentary fs on this if built with "cold=1"
    rk0 - 4871 blocks

u0.s sets up rf0 as:

    - superblock layout
      - free storage map contains 128 bytes
      - inode map contains 64 bytes

    - allocate top 64 blocks "to unix"  (960..1023)
    - allocate 17 blocks per process (nproc) (688..960 - 16 procs)
    - free blocks 687..34
    - zero out blocks 33..1 for use as inodes
      (and 2nd half of superblock which is unused?)

    - for each special inode i-1 to i-40 initialize it
      - mode 100017 (allocated, read, write, other read, othe write)
      - num links = 1
      - uid = 1 (yup, not root)
      - fill in timestamp info

   - write out premade i-nodes on i-41 .. i-47
     with premade directory data.
     i-41 root (with dev, bin, etc, usr, tmp)
     i-42 dev (with tty, ppt, mem, rf0, rk0, tap0 .. tap7, tty0..tty7, lpr, 
     i-43 bin (empty)
     i-44 etc (with init)
     i-45 usr (empty)
     i-46 tmp (empty)
     i-47 init (binary, included in u0.s)
          special version that opens /dev/tap0 and reads files from it,
          creates them, chmods them and chowns them

Tim Newsham

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