linux-kernel - Re: [PATCH 1/3] firmware: introduce sysfs driver for QEMU's fw

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Message-ID: <20150810191509.GA7264@kroah.com>
Date:	Mon, 10 Aug 2015 12:15:09 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	"Gabriel L. Somlo" <somlo@....edu>
Cc:	ralf@...ux-mips.org, zajec5@...il.com, paul@...an.com,
	galak@...eaurora.org, linux-api@...r.kernel.org,
	linux-kernel@...r.kernel.org, matt.fleming@...el.com,
	x86@...nel.org, linux-efi@...r.kernel.org, qemu-devel@...gnu.org,
	lersek@...hat.com, jordan.l.justen@...el.com,
	gleb@...udius-systems.com, pbonzini@...hat.com, kraxel@...hat.com,
	eblake@...hat.com, rjones@...hat.com,
	kernelnewbies@...nelnewbies.org
Subject: Re: [PATCH 1/3] firmware: introduce sysfs driver for QEMU's fw_cfg
 device

On Mon, Aug 10, 2015 at 03:02:22PM -0400, Gabriel L. Somlo wrote:
> Mainly, qemu's fw_cfg is a read-only "device", so one wouldn't ever
> care to try writing anything to it. /sys/firmware/... feels like a fit
> because fw_cfg contains binary blobs originally meant to be used by
> the bios (it's how SeaBIOS and OVMF pull smbios and acpi tables out of
> the host and set them up in guest memory before booting the guest kernel,
> as one of the many examples).
> 
> The most similar example (and the existing driver I used as an example
> during implementation) is dmi-sysfs.c, which also exposes all the
> metadata for each smbios table as numeric (or string) read-only attributes,
> and has a "raw" attribute which allows dumping each table in its
> entirety. Same thing here -- I want to expose the name, size, and
> select key for each blob, but also allow access to the "payload", i.e.
> the blob itself.

That's great, and you can have these "blobs" be an attribute for a
struct device.  Just using a "raw" kobject as you are is hard, as you
have seen, and messy.  Making it a "real" device makes this all much
easier and simpler.

Now if you want to keep things in /sys/firmware/ that's another issue,
and would have to stay as a kobject.  so maybe it does need to remain,
need to think about that...

thanks,

greg k-h
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