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

[Glauber Costa <glommer@gmail.com>]

On Fri, Mar 27, 2009 at 8:12 PM, Carl-Daniel Hailfinger
<c-d.hailfinger.devel.2006@gmx.net> wrote:
> 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.

Such a check already exists.

-- 
Glauber  Costa.
"Free as in Freedom"
http://glommer.net

"The less confident you are, the more serious you have to act."