Re: [Xen-devel] [Qemu-devel] [PATCH] Do not emulate a floppy drive when -nodefaults

[John Snow <jsnow@xxxxxxxxxx>]

On 05/14/2015 10:07 AM, Michael S. Tsirkin wrote:
> On Thu, May 14, 2015 at 02:02:04PM +0200, Markus Armbruster wrote:
>> Correct.
>>
>> Here's how I think it should be done:
>>
>> * Create a machine option to control the FDC
>>
>>   This is a machine-specific option.  It should only exist for machine
>>   types that have an optional FDC.
>>
>>   Default must be "on" for old machine types.  Default may be "off" for
>>   new machine types.
>>
>>   It should certainly be off for pc-q35-2.4 and newer.  Real Q35 boards
>>   commonly don't have an FDC (depends on the Super I/O chip used).
>>
>>   We may want to keep it off for pc-i440fx-2.4 and newer.  I doubt
>>   there's a real i440FX without an FDC, but our virtual i440FX is quite
>>   unlike a real one in other ways already.
> 
> I think making it off by default is a bad idea, it will break
> command-line users.
> 
> 

If we can add a flag to disable it, I still think I wouldn't mind that,
if it could be worked out to not be hacky and gross.

>> * Create the FDC only if the option is "on".
>>
>> * Optional: make -drive if=floppy,... auto-enable it
> 
> Every time we do such auto hacks, we regret this later.
> Just do what we are told, fail if=floppy if disabled.
> 

I agree very much. Just because the current drive/device syntax is
almost totally hosed doesn't mean we should put more wood on the fire.

>>   I wouldn't bother doing the same for -global isa-fdc.driveA=... and
>>   such.
>>
>> Stefano, if you're willing to tackle this, go right ahead!


I'm definitely against a "--seriously-nothing" flag because the line for
what is embedded or not is fuzzy. Paolo raises some good points against
where you draw the line for what we decide to allow users to
include/exclude that is otherwise considered part of the board.

Still, given the hype train, if there is an API we could introduce that
is likely not to make our code gross (or make us belly-ache about how
dumb we were in 5 years) that disables the FDC, I don't think I would
mind terribly. I'll leave that to minds more opinionated than mine to
hash out, though.

Maybe the best option here really is to carefully separate optional from
non-optional components (FDC vs. Floppy Drive, Floppy Disk code) and
just give the core FDC code a good scrubbing.

--js

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