Re: [PATCH v3 0/4] SysFS driver for QEMU fw_cfg device

[Gabriel L. Somlo]

On Mon, Oct 05, 2015 at 01:23:33PM +0100, Mark Rutland wrote:
> On Mon, Oct 05, 2015 at 01:48:52PM +0200, Paolo Bonzini wrote:
> > 
> > 
> > On 05/10/2015 12:00, Mark Rutland wrote:
> > > Some of the keys in the example look like they'd come from other sources
> > > (e.g. the *-tables entries), while others look like kernel/bootloader
> > > configuration options (e.g. etc/boot-fail-wait, bootorder) -- I'm
> > > concerned about redundancy here.
> > 
> > The redundancy is because the firmware and the bootloader actually
> > _consume_ these fw_cfg strings to produce the others (the ACPI tables,
> > the kernel configuration options).
> > 
> > On the other hand, hiding some strings just because they ought to have
> > been consumed already makes little sense.
> 
> Sure. However, I'm concerned that providing redundant interfaces for
> those could lead to people grabbing information from here (because it's
> convenient) rather than the existing canonical locations, which means we
> get more software that works on fewer systems for no good reason.
> 
> What I couldn't figure out was what _additional_ information this
> provided; it looked like a mixed bag of details we could already get
> from disparate sources. If that's all it does, then it seems to me like
> it doesn't add any benefit and potentially makes things worse.
> 
> So what do we get from this interface that we cannot get elsewhere, and
> why is this the best way of exposing it?

Starting with qemu 2.4, it is possible to insert arbitrary named
blobs into fw_cfg from the qemu command line. *Those* entries
might be interesting to userspace, which is why it might be handy
to access to fw_cfg blobs in general.

Thanks,
--Gabriel
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