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