[TUHS] Compiling the unix v5 kernel

[Warren Toomey]

here's the e-mail that I sent on to Mark in the hope that it would
give him enough information to get his 5th Edition kernel working
with a tape device. He has also now joined the list. Welcome aboard, Mark.

	Warren

----- Forwarded message from Warren Toomey <wkt at tuhs.org> -----

On Thu, Jul 10, 2014 at 05:56:04PM -0400, Mark Longridge wrote:
> There was no m40.s in v5 so I substituted mch.s for m40.s and that
> seemed to create a kernel and it booted but I can't access /dev/mt0.

Mark, glad to hear you were able to rebuild the kernel. I've never tried
on 5th Edition. Just reading through the 6th Edition docs, it says this:

-----
     Next  you  must  put in all of the special files in the
directory /dev using mknod‐VIII.   Print  the  configuration
file  c.c created above.  This is the major device switch of
each device class (block and character).  There is one  line
for  each  device  configured in your system and a null line
for place holding for those  devices  not  configured.   The
block special devices are put in first by executing the fol‐
lowing generic command for each disk or tape  drive.   (Note
that  some  of  these  files  already exist in the directory
/dev.  Examine each file with ls‐I with −l flag  to  see  if
the file should be removed.)

          /etc/mknod /dev/NAME b MAJOR MINOR

The NAME is selected from the following list:

     c.c  NAME device
     rf   rf0  RS fixed head disk
     tc   tap0 TU56 DECtape
     rk   rk0  RK03 RK05 moving head disk
     tm   mt0  TU10 TU16 magtape
     rp   rp0  RP moving head disk
     hs   hs0  RS03 RS04 fixed head disk
     hp   hp0  RP04 moving head disk

The  major  device  number  is selected by counting the line
number (from zero) of the device’s entry in the  block  con‐
figuration  table.  Thus the first entry in the table bdevsw
would be major device zero.

     The minor device is the drive number,  unit  number  or
partition as described under each device in section IV.  The
last digit of the name (all given as 0 in the  table  above)
should reflect the minor device number.  For tapes where the
unit is dial selectable, a special file may be made for each
possible selection.

     The  same  goes  for  the  character devices.  Here the
names are arbitrary except that devices meant to be used for
teletype  access  should  be named /dev/ttyX, where X is any
character.  The files tty8 (console), mem,  kmem,  null  are
already correctly configured.

     The  disk and magtape drivers provide a ‘raw’ interface
to the device which provides direct transmission between the
user’s  core  and  the  device and allows reading or writing
large records.  The raw device counts as a character device,
and should have the name of the corresponding standard block
special file with ‘r’ prepended.  Thus the raw magtape files
would be called /dev/rmtX.

     When  all  the  special  files  have been created, care
should be taken to change  the  access  modes  (chmod‐I)  on
these files to appropriate values.
-----

Looking at the c.c generated, it has:

int     (*bdevsw[])()
{
        &nulldev,       &nulldev,       &rkstrategy,    &rktab,
        &tmopen,        &tmclose,       &tmstrategy,    &tmtab,		/* 1 */
        &nulldev,       &tcclose,       &tcstrategy,    &tctab,
        0
};

int     (*cdevsw[])()
{
        &klopen,   &klclose,   &klread,   &klwrite,   &klsgtty,
        &nulldev,  &nulldev,   &mmread,   &mmwrite,   &nodev,
        &nulldev,  &nulldev,   &rkread,   &rkwrite,   &nodev,
        &tmopen,   &tmclose,   &tmread,   &tmwrite,   &nodev,		/* 3 */
        &dcopen,   &dcclose,   &dcread,   &dcwrite,   &dcsgtty,
        &lpopen,   &lpclose,   &nodev,    &lpwrite,   &nodev,
        0
};

Following on from the docs, you should be able to make the /dev/mt0
device file by doing:

	/etc/mknod /dev/tm0 b 1 0

And possibly also:

	/etc/mknod /dev/rmt0 c 3 0

Cheers,
	Warren