Date: Mon, 10 Aug 2015 12:15:09 -0700
From: Greg KH <gregkh@linuxfoundation.org>
To: "Gabriel L. Somlo" <somlo@cmu.edu>
Cc: ralf@linux-mips.org, zajec5@gmail.com, paul@pwsan.com,
        galak@codeaurora.org, linux-api@vger.kernel.org,
        linux-kernel@vger.kernel.org, matt.fleming@intel.com, x86@kernel.org,
        linux-efi@vger.kernel.org, qemu-devel@nongnu.org, lersek@redhat.com,
        jordan.l.justen@intel.com, gleb@cloudius-systems.com,
        pbonzini@redhat.com, kraxel@redhat.com, eblake@redhat.com,
        rjones@redhat.com, kernelnewbies@kernelnewbies.org
Subject: Re: [PATCH 1/3] firmware: introduce sysfs driver for QEMU's fw_cfg
 device
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 <3b039351aba44759627fa77a0003dad685a9f21d.1439220623.git.somlo@cmu.edu>
 <20150810183054.GA18817@kroah.com>
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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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