Date: Sat, 19 Dec 2015 10:10:07 -0500
From: "Gabriel L. Somlo" <somlo@cmu.edu>
To: Pavel Machek <pavel@ucw.cz>
Cc: gregkh@linuxfoundation.org, robh+dt@kernel.org, pawel.moll@arm.com,
        mark.rutland@arm.com, ijc+devicetree@hellion.org.uk,
        galak@codeaurora.org, arnd@arndb.de, lersek@redhat.com,
        ralf@linux-mips.org, rmk+kernel@arm.linux.org.uk, eric@anholt.net,
        hanjun.guo@linaro.org, zajec5@gmail.com, sudeep.holla@arm.com,
        agross@codeaurora.org, linux-api@vger.kernel.org,
        linux-kernel@vger.kernel.org, devicetree@vger.kernel.org,
        qemu-devel@nongnu.org, jordan.l.justen@intel.com, mst@redhat.com,
        peter.maydell@linaro.org, leif.lindholm@linaro.org,
        ard.biesheuvel@linaro.org, pbonzini@redhat.com, kraxel@redhat.com,
        luto@amacapital.net, stefanha@gmail.com, revol@free.fr,
        matt@codeblueprint.co.uk
Subject: Re: [PATCH v6 0/4] SysFS driver for QEMU fw_cfg device
Message-ID: <20151219151006.GA11545@GLSMBP.INI.CMU.EDU>
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 <20151217160923.GI19448@HEDWIG.INI.CMU.EDU>
 <20151219091228.GA6024@amd>
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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
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