Re: [Qemu-devel] [PATCH V4 4/4] fw_cfg: insert fw_cfg file blobs via qemu cmdline

[Laszlo Ersek <lersek@redhat.com>]

On 06/01/15 12:43, Paolo Bonzini wrote:
> 
> 
> On 01/06/2015 12:23, Michael S. Tsirkin wrote:
>> Still, reserving part of the namespace for QEMU internal use
>> is *not* policy, it's just good engineering.
>>
>> How about we forbid adding files under "etc/" ?
>>
>> That would be enough to avoid conflicts.
> 
> I do not understand.  What we're doing is free-beer.  We can always say
> no.  What's your worry?
> 
> One usecase of this feature is to avoid recompiling QEMU while playing
> with firmware.  If you cannot mimic QEMU's behavior (which is to add
> "etc/" files), the feature is pointless, or at least I totally cannot
> understand its purpose and I'm against merging it.

As far as I understand, the goal is indeed to expose fw_cfg to the host
user, without having to recompile QEMU. This would allow site-specific
fw_cfg files, for site-specific guest features. Gabriel wanted to
control some guest-agent like functionality (on windows too) with it,
IIRC. Matt Fleming @Intel might use it for custom OVMF development.

I think those are valid goals and should be possible to support even if
we isolate QEMU's own fw_cfg namespace strictly from the user (opt/)
namespace. This feature is not there to mess with QEMU's "own" fw_cfg
files; for those the existent command line switches should be used.

Thanks
Laszlo