Re: [Qemu-devel] [PATCH v6 0/4] SysFS driver for QEMU fw_cfg device

[Gabriel L. Somlo]

Hi Pavel,

On Sat, Dec 19, 2015 at 10:12:28AM +0100, Pavel Machek wrote:
> On Thu 2015-12-17 11:09:23, Gabriel L. Somlo wrote:
> > ping ?
> > 
> > Also, for the corresponding patch set on the QEMU end of things,
> > ping on http://thread.gmane.org/gmane.comp.emulators.qemu/376321
> 
> I guess missing information is why such access is a good
> idea. Debugging?

Debugging did come up in earlier threads as well. However, personally,
I am interested in a mechanism for the host to pass information to the
guest in a way that's both

        - asynchronous: i.e., host doesn't need to wait for guest to
          be ready to accept data (e.g. by first starting an agent)

        - out-of-band: don't commandeer guest elements normally visible
          and available to guest *users* (e.g. kernel command line,
          mount a floppy/cdrom image, etc).

QEMU now allows arbitrary fw_cfg blobs to be added via the command
line, so it would be nice to make it easy to access them from the
guest OS -- and what's nicer and easier than:

        cat /sys/firmware/qemu-fw-cfg/.../some-blob-name/raw

Thanks,
--Gabriel

> > On Fri, Dec 04, 2015 at 10:29:02AM -0500, Gabriel L. Somlo wrote:
> > > Allow access to QEMU firmware blobs, passed into the guest VM via
> > > the fw_cfg device, through SysFS entries. Blob meta-data (e.g. name,
> > > size, and fw_cfg key), as well as the raw binary blob data may be
> > > accessed.
> > > 
> > > The SysFS access location is /sys/firmware/qemu_fw_cfg/... and was
> > > selected based on overall similarity to the type of information
> > > exposed under /sys/firmware/dmi/entries/...
> 
> -- 
> (english) http://www.livejournal.com/~pavelmachek
> (cesky, pictures) 
> http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html