[PATCH] docs: Discourage users from using fwcfg

[Daniel P. Berrangé]

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

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.

Regards,
Daniel
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