[Qemu-devel] How to correctly use more than 2 floppy drives?

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

Hi,

I am trying to understand the possible values for the MAX_FD variable
used by the floppy controller model (hw/block/fdc.c).

Looking at git history:

- 2004-01-05 7138fcfbf7dd + 8977f3c107ef (Jocelyn Mayer):
  FDC introduced with "#define MAX_FD 2"

- 2008-04-29 78ae820cfeb0 (Hervé Poussineau):
  Supports up to 4 floppy drives if MAX_FD is set to 4
  Migration stream knows about runtime value of MAX_FD

- 2009-09-10 d7a6c2703577 (Juan Quintela):
  FDC vmstate-ified
  Migration stream use compile time value of MAX_FD

Since 7138fcfbf7dd MAX_FD has always been defined as 2.

Since d7a6c2703577 MAX_FD can not be different than 2 without breaking
migration.

If I understand correctly migration, first we should change in
vmstate_fdc the user-definable MAX_FD by a constant 2 value.

Then to be able to use >2 floppy disks I have to modify the the
vmstate.version_id, and

1/ add a new field in the vmstate_fdc containing the number of drives
and add code to check >2 and adapt

or

2/ change MAX_FD to 4 for all the codebase, adding some code to migrate
to older FDC with only 2 disks...

Another option I don't like is:

3/ get ride of MAX_FD != 2 and clean the codebase...

$ git grep '#if MAX_FD'
hw/block/fdc.c:744:#if MAX_FD == 4
hw/block/fdc.c:758:#if MAX_FD == 4
hw/block/fdc.c:1317:#if MAX_FD == 4
hw/block/fdc.c:1340:#if MAX_FD == 4
hw/block/fdc.c:2041:#if MAX_FD == 4
hw/block/fdc.c:2079:#if MAX_FD == 4
hw/block/fdc.c:2104:#if MAX_FD == 4

Hervé, what board are/were you using with 4 floppy drives?

BTW this link is somehow interesting :)
https://www.seasip.info/VintagePC/floppies.html

Thanks,

Phil.