Re: missing boot rom: is it really a fatal error?

[Markus Armbruster <armbru@redhat.com>]

"Michael S. Tsirkin" <mst@redhat.com> writes:

> On Sun, May 07, 2023 at 08:56:23PM +0300, Michael Tokarev wrote:
>> Hi!
>> 
>> In old good world ;), there was qemu which didn't require boot roms to be present
>> for all devices for which bootrom file is defined, missing rom was just a warning.
>> But this changed in 2014, 9 years ago, with this commit:
>> 
>> commit 178e785fb4507ec3462dc772bbe08303416ece47
>> From: Marcel Apfelbaum <marcel.a@redhat.com>
>> Date: Mon, 27 Oct 2014 19:34:41 +0200
>> Subject: [PATCH] hw/pci: fixed error flow in pci_qdev_init
>> 
>>   Verify return code for pci_add_option_rom.
>> 
>> where inability to load rom file started being treated as an error.
>> Up until now I didn't even know about this change, until today when someone bugged
>> me about non-working qemu on debian, due to missing network boot roms (this a
>> packaging issue due to me being unaware of the above change).
>> 
>> What is the reason to require boot roms to be present and throw an error if not?
>> 
>> I'm about to revert that old change on debian, to make it just a warning instead
>> of an error (the code is different now, but the same principle applies), - because
>> I dislike dependencies which are useless 99.9% of the time and are trivial to
>> install when actually needed.
>> 
>> Thanks,
>> 
>> /mjt
>> 
>
> I advise against it.
> If you boot guest on a system with boot rom not installed you will not
> be able to migrate to a system with boot rom installed.
> why not? because we don't know how big to make the rom BAR.

For what it's worth: we know when property "romsize" is set.

> And users will not discover until much much later after they have
> painted themselves into a corner.