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Re: [Qemu-devel] How to correctly use more than 2 floppy drives?
From: |
Hervé Poussineau |
Subject: |
Re: [Qemu-devel] How to correctly use more than 2 floppy drives? |
Date: |
Fri, 5 Apr 2019 18:35:41 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 |
Le 05/04/2019 à 12:29, Philippe Mathieu-Daudé a écrit :
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?
That was only an attempt to support 4 drives in code, as controller was able to
do it.
However, no emulated board took advantage of it, so that's why it kind-of
regressed.
Feel free to choose the solution you prefer.
Hervé
BTW this link is somehow interesting :)
https://www.seasip.info/VintagePC/floppies.html
Thanks,
Phil.