[PATCH] docs: Discourage users from using fwcfg

[Laszlo Ersek]

On 09/08/20 19:26, Daniel P. Berrangé wrote:
> On Tue, Sep 08, 2020 at 10:17:08AM +0200, Laszlo Ersek wrote:
>> On 09/07/20 16:38, Daniel P. Berrangé wrote:
>>> On Mon, Sep 07, 2020 at 04:20:02PM +0200, Michal Privoznik wrote:
>>>> On 9/7/20 3:57 PM, Martin Kletzander wrote:
>>>>> On Mon, Sep 07, 2020 at 03:48:16PM +0200, Michal Privoznik wrote:
>>>>>> Even though this was brought up in upstream discussion [1] it
>>>>>> missed my patches: users should prefer <oemStrings/> over fwcfg.
>>>>>> The reason is that fwcfg is considered somewhat internal to QEMU
>>>>>> and it has limited number of slots and neither of these applies
>>>>>> to <oemStrings/>.
>>>>>>
>>>>>> While I'm at it, I'm fixing the example too (because it contains
>>>>>> incorrect element name) and clarifying sysfs/ exposure.
>>>>>>
>>>>>> 1: https://www.redhat.com/archives/libvir-list/2020-May/msg00957.html
>>>>>>
>>>>>> Reported-by: Laszlo Ersek <lersek at redhat.com>
>>>>>> Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
>>>>>> ---
>>>>>> docs/formatdomain.rst | 14 +++++++++-----
>>>>>> 1 file changed, 9 insertions(+), 5 deletions(-)
>>>>>>
>>>>
>>>>
>>>>> It's nice that you say that, but people who would like to use fw_cfg for
>>>>> passing
>>>>> in a huge blob, which is saved in a file, will read this, go to
>>>>> <oemStrings/>
>>>>> and see that there is no way to pass a file as an input.  Should that be
>>>>> dealt
>>>>> with somehow?  Or would that be discouraged as well?
>>>>
>>>> Unfortunately, QEMU doesn't allow reading OEM strings from a file (at least
>>>> quick glance over hw/smbios/smbios.c doesn't show any signs it's allowed).
>>>
>>> Indeed, that is an RFE I've never got around to
>>
>> Yes, I remember that -- I remember that we discussed this, and also that
>> you didn't have time for it. Which is entirely justifiable; other stuff
>> has been (and continues to be) more important.
>>
>> For reference, here's the launchpad ticket that tracks the RFE for QEMU:
>>
>>   https://bugs.launchpad.net/qemu/+bug/1826200
> 
> I spent some time today (more than expected in fact!) implementing
> this....
> 
>   https://lists.gnu.org/archive/html/qemu-devel/2020-09/msg03023.html

That was quick! Thank you!

> I hit a possible EDK2 bug when SMBIOS 3.0 where it hangs when the
> size exceeds about 128 KB, but I don't intend to investigate it
> further.

I'll look into it.

Thanks!
Laszlo