linux-kernel - Re: [PATCH v8 0/4] SysFS driver for QEMU fw

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Date:	Wed, 3 Feb 2016 22:47:29 +0000
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	"Gabriel L. Somlo" <somlo@....edu>
Cc:	gregkh@...uxfoundation.org, robh+dt@...nel.org, pawel.moll@....com,
	mark.rutland@....com, ijc+devicetree@...lion.org.uk,
	galak@...eaurora.org, arnd@...db.de, lersek@...hat.com,
	ralf@...ux-mips.org, rmk+kernel@....linux.org.uk, eric@...olt.net,
	hanjun.guo@...aro.org, zajec5@...il.com, sudeep.holla@....com,
	agross@...eaurora.org, linux-api@...r.kernel.org,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	qemu-devel@...gnu.org, mst@...hat.com, imammedo@...hat.com,
	peter.maydell@...aro.org, leif.lindholm@...aro.org,
	ard.biesheuvel@...aro.org, pbonzini@...hat.com, kraxel@...hat.com,
	ehabkost@...hat.com, luto@...capital.net, stefanha@...il.com,
	revol@...e.fr, rth@...ddle.net
Subject: Re: [PATCH v8 0/4] SysFS driver for QEMU fw_cfg device

On Thu, 28 Jan, at 09:23:10AM, Gabriel L. Somlo wrote:
> From: "Gabriel Somlo" <somlo@....edu>
> 
> 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?