qemu broke booting of old RedHat floppies

From: Michael Tokarev <mjt@tls.msk.ru>
To: qemu-devel qemu-devel <qemu-devel@nongnu.org>,
	John Snow <jsnow@redhat.com>
Subject: qemu broke booting of old RedHat floppies
Date: Wed, 20 Jan 2021 18:11:41 +0300	[thread overview]
Message-ID: <0bca1cd0-69c3-c07a-b4cf-015dcdbc6d61@msgid.tls.msk.ru> (raw)

As someone noticed on IRC, old (2.x) RedHat floppies does not boot
in current qemu.  When qemu is booted from floppy image at
  https://archive.org/details/RedHatLinuxBootDisk521998
(download the "ISO image" link there, it really is an 1.44 floppy),
seabios says Boot failed and that's it.

I run git bisect with it, knowing that qemu 2.1 works fine, and
it pointed out to this commit which is oldish qemu-2.5+:

commit 4812fa27fa75bce89738a82a191755853dd88408
Author: John Snow <jsnow@redhat.com>
Date:   Fri Jan 22 15:51:05 2016 -0500

     fdc: change auto fallback drive for ISA FDC to 288

     The 2.88 drive is more suitable as a default because
     it can still read 1.44 images correctly, but the reverse
     is not true.

     Since there exist virtio-win drivers that are shipped on
     2.88 floppy images, this patch will allow VMs booted without
     a floppy disk inserted to later insert a 2.88MB floppy and
     have that work.

     This patch has been tested with msdos, freedos, fedora,
     windows 8 and windows 10 without issue: if problems do
     arise for certain guests being unable to cope with 2.88MB
     drives as the default, they are in the minority and can use
     type=144 as needed (or insert a proper boot medium and omit
     type=144/288 or use type=auto) to obtain different drive types.

     As icing, the default will remain auto/144 for any pre-2.6
     machine types, hopefully minimizing the impact of this change
     in legacy hw to basically zero.

     Reviewed-by: Eric Blake <eblake@redhat.com>
     Signed-off-by: John Snow <jsnow@redhat.com>
     Message-id: 1453495865-9649-13-git-send-email-jsnow@redhat.com

Now, I don't even know where to put that "type=144/288/auto" thing,
I tried this:

  -drive file=RedHatLinuxBootDisk521998.disk1of1.img,if=floppy,format=raw,type=144

but it says that format=raw does not support "type=144" option.

And it's even more: I don't remember which size should be an 1.44Mb floppy :))
The file size of that image is 1492992 bytes which does not look like it is of
standard size, but I can't find which size it should be.

Thanks!

/mjt