Re: [Qemu-devel] [PATCH] get roms more room.

[Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@gmx.net>]

On 27.03.2009 21:45, Glauber Costa wrote:
> On Fri, Mar 27, 2009 at 5:29 PM, Carl-Daniel Hailfinger
> <c-d.hailfinger.devel.2006@gmx.net> wrote:
>   
>> On 27.03.2009 18:37, Glauber Costa wrote:
>>     
>>> This patch increases by 50 % the size available for option roms.
>>> The main motivator is that some roms grew bigger than the 64k we
>>> currently allocate for them (Hey, it's 2009!)
>>>
>>> One example is the gpxe project, that produces some roms with 69k,
>>> 70k, etc. The space proposed by this patch actually makes it as
>>> big as 84k. Probably still a fit for some time.
>>>
>>> But there is no free lunch. This space must come from somewhere,
>>> and we take it from vga rom space. Currently, our vga roms are
>>> around 35k in size. With this patch, they will be limited to
>>> 44k, instead of 64k, which seems reasonable to me.
>>>
>>>       
>> As a firmware developer, I have to speak up here. Although I agree that
>> option ROMs may be bigger than 64k, replacing one hardcoded magic limit
>> with another hardcoded magic limit seems to be a bit questionable.
>>
>> If you really want to hardcode this instead of calculating it
>> dynamically, please use at least some symbolic constants and tell the
>> user to change the symbolic constants and recompile Qemu if he hits the
>> size limit.
>>
>> This patch reduces the room for the VGA option ROM without checking for
>> its size. If we perform option ROM size checks, we may as well not
>> exclude the VGA option ROM from that check.
>>     
>
> We load the VGA rom before loading any option roms. Would you be
> okay with an approach that loads the vga rom, round up its size to the
> next boundary, and assign the remaining space to option roms?
>   

Excellent idea.
Could you please change the error message to tell the user that
VGA+other option ROMs may not exceed a total size?
A check for VGA ROM size to be less than the total allowed size may be
useful to prevent underflows in calculations of the remaining space for
other option ROMs.


Regards,
Carl-Daniel

-- 
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