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Using netboot Debian installation images in the Hercules emulator

Most posts to the various Debian mailing lists are a question looking
for an answer.  This one is different.  This one is an answer looking
for a question.

Maybe I'm the only dolt who didn't already know this; but I just
figured something out; and just on the off chance that someone else
might not know this; I thought I'd share what I've learned.  For those
of you who already know this, please excuse the noise.

The netboot Debian installation images which are designed for use in
a virtual card reader in a virtual machine under z/VM work just fine
when installing "natively" in the Hercules emulator in a "real" card
reader.  Consider, for example, the following device definition in

000C 3505 /home/hercules/reader/kernel.debian /home/hercules/reader/parmfile.debian /home/hercules/reader/initrd.debian ebcdic autopad eof

(Regardless of how the above may look in your mail reader, the above is
actually one logical line.)  000C is the device number; 3505 is the
device type; then there are the three netboot image files in the proper
order; then Hercules options are after that.  The ebcdic option tells
Hercules not to do any ascii-to-ebcdic translation on the input files,
nor to look for line-feed characters as an indicator of logical records,
but to simply split up the input file into 80-byte pieces and pass each
piece as a separate card image to the program which is reading from the
card reader.  The autopad option tells Hercules to pad the last record
of each file to a length of 80 bytes with null characters (0x00) to make
the last record 80 bytes long, if the input file size is not a multiple
of 80 bytes.  The eof option tells Hercules to signal end-of-file
(unit exception in the device status) on the first read following the
end of each file.  An attention interruption will then be signaled by
Hercules when it is ready for the program to read the next file.  (No
attention interruption is signaled after the last file.)  Note that the
multifile option must *not* be used.  If the multifile option is used,
end-of-file is signaled only once (at the end of the last file).  The
three files are treated as one continuous file in that case.  This is
the equivalent of spooling a virtual reader continuous (CONT) in z/VM,
and that will not produce the expected results.

There is no need to do a list-directed IPL from a CD image, there is no
need to create an emulated tape file, etc.  Just use the netboot images
directly.  There is not even a need to pad the files to a multiple of
80 bytes, thanks to the autopad option.  You can use them "as is".  You
boot the installer by entering the "ipl 000C" command on the Hercules
console, of course.  (Or you may use "iplc 000C" if you want to do a
"load clear" instead of a "load normal".)  I hope this helps someone.

  .''`.     Stephen Powell    
 : :'  :
 `. `'`

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