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

[Markus Armbruster]

Hervé Poussineau <address@hidden> writes:

> 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.

Since no user has appeared since 2008, it feels safe enough to assume
that none will appear going forward.  I lean towards your "3/ get ride
of MAX_FD != 2 and clean the codebase..."  Explain in a comment that we
emulate only a 2-drive floppy controller, not the genuine IBM PC 4-drive
floppy controller.