On Thu, 28 Jan, at 09:23:10AM, Gabriel L. Somlo wrote:

From: "Gabriel Somlo" <somlo-D+Gtc/HYRWM@public.gmane.org>

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/...

This functionality is primarily intended to serve as a host->guest
configuration data transfer mechanism that is both:

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

        - out-of-band:  there is no need to commandeer a guest element
                        normally visible and available to the guest user
                        (e.g., kernel cmdline, mounting floppy/cdrom, etc.)

QEMU now allows arbitrary fw_cfg blobs to be added via the command line,
so it would be nice to make them easy to retrieve from within the guest
OS, and the niceset and easiest way I can think of is

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

New since v7:

	- kbuild testbot complained about a warning on ia64, so limit
	  the availability of fw_cfg in Kconfig to only architectures
	  on which QEMU makes it available, which include:

		(ARM || ARM64 || PPC_PMAC || SPARC || X86)

This is looking pretty good now. Does anyone have remaining
objections before this gets merged?