Re: [Qemu-devel] Re: qdev property bug?

[Michael S. Tsirkin]

On Mon, Dec 14, 2009 at 01:33:50PM -0600, Anthony Liguori wrote:
> Sebastian Herbszt wrote:
>> Anthony Liguori wrote:
>>> Michael S. Tsirkin wrote:
>>>>
>>>> Further, we should error out when device is added.
>>>> Doing this during boot is way too late, management
>>>> won't be able to understand such errors and
>>>> won't be able to recover.
>>>>   
>>>
>>> I don't quite understand this.
>>>
>>> In 0.11, we never loaded option roms unless a user specified -boot  
>>> n.  If a user specified -boot n and used more than one nic type, I'm  
>>> fairly certain it would error out during start up because it would  
>>> run out of option rom space.  Maybe it required three types of nics,  
>>> but the point still remains.
>>
>> I think it used to be possible to have two different nic types and  
>> only load
>> one rom, e.g. -net nic,model=pcnet -net nic,model=e1000 -option-rom  
>> e1000.rom
>> Then use the boot menu to select the e1000 nic.
>
> That's a super hack :-)  The fact that works is pure luck.
>
>>> In 0.12, we always load the option rom for a PCI device.  An easy  
>>> solution here would be to just gracefully handle the case where we  
>>> ran out of option rom space and (silently) stop loading additional  
>>> roms.  With respect to -boot n, it makes the behavior buggy (you  
>>> cannot boot from the second nic) but my original point is that that  
>>> is not a regression from 0.11.
>>
>> Even if i repeat myself [1] i suggest putting an option-rom loading  
>> flag to the -net option:
>> -net nic,model=e1000,rom=[on,off,e1000.bin]
>
> Well it ought to be a qdev property and it ought to be applicable to  
> every PCI device.
>
>>> For 0.13, we should probably allow a user to suppress option rom  
>>> loading for a given PCI device.  The limited space is a pretty good  
>>> justification for that.
>>
>> The default behaviour should be not loading option-roms; users should  
>> request those.
>
> I disagree.  A user should not have to decide whether they want PXE boot  
> or not when they create a VM.

At some level this is wrong. ROM presence is a hardware feature and you
definitely need to select your hardware when you create a VM.  For real
hardware, cards with PXE are sometimes more expensive than without as
they need ROM memory.  People do select hardware based on this.

Even when PXE is present in hardware, most BIOS
vendors will let you turn it on/off optionally,
for security if not for other reasons.

What the default should be depends on whether the
majority of our users use PXE. I guess not,
and if I am right default should be off.

>  The less decisions a user has to make up  
> front the easier qemu is to use.
>
> Regards,
>
> Anthony Liguori