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

[Michael S. Tsirkin]

On Mon, Dec 14, 2009 at 02:43:38PM -0600, Anthony Liguori wrote:
> Michael S. Tsirkin wrote:
>> On Mon, Dec 14, 2009 at 09:32:30PM +0100, Gerd Hoffmann wrote:
>>   
>>> On 12/14/09 21:20, Michael S. Tsirkin wrote:
>>>     
>>>>> So far, it's not clear to me that anyone has demonstrated how this is
>>>>> harmful for people that don't want pxe booting.  Assuming we fix the bug
>>>>> about rom loading, then there's really no impact to users.
>>>>>         
>>> Fix (v2) is on the list already.
>>>
>>>     
>>>> PXE booting might have security impact. You do not want to
>>>> do this if you are on a hostile network.
>>>>       
>>> Option rom loaded doesn't imply pxe boot will be tried.  It only 
>>> means  PXE boot can be selected, either via
>>>
>>>   -boot order=[something with 'n' here]
>>>
>>> or via
>>>
>>>   -boot menu=on + F12 + picking menu entry
>>>
>>> By default qemu doesn't try to PXE-boot, even if no other bootable   
>>> device is available.
>>>
>>> cheers,
>>>   Gerd
>>>     
>>
>> I guess so. But then, why are we loading it in BIOS
>> and wasting memory? Let's only shadow the ROM
>> when PXE is selected?
>>   
>
> Because it can be selected by the user via the menu and because it can  
> be selected at runtime via the boot_set monitor command.

Yes, but it's not like we have nowhere to store them.
We could shadow ROM when it is actually needed.

> Also, the comment about "wasting memory" not quite accurate.  The memory  
> region in question is only used for roms.  If we didn't put roms there,  
> it would go to waste.

Some BIOSes I saw have an option not to use the first 1M for rom
shadowing :). Seriously as you see we are already
running out of that 1M.

> Currently, the only roms we load are pxe roms or things specified by  
> -option-rom.  You could certainly argue that making -option-rom higher  
> priority than implicit pxe roms is valuable but removing the pxe roms  
> really serves no purpose.
>
> Regards,
>
> Anthony Liguori

I am concerned about management.  User selects "PXE support" when
creating VM, and creationg succeeds, but in fact PXE can not work
because we can not shadow the ROM.

Sounds bad. If device creation failed,
user would get feedback when it is expected.

-- 
MST