[PATCH v5 0/4] SysFS driver for QEMU fw_cfg device

Gabriel L. Somlo
2015-11-23T15:57:40Z

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/...

New since v4:

Documentation (Patches 1/4 and 4/4) now points to the authoritative
file in the QEMU source tree for any details related to the "hardware
interface" of the fw_cfg device; Only details specific to sysfs (1/4)
and DT (4/4) should stay in the kernel docs.

Thanks,
--Gabriel

>New (since v3):
>
> Patch 1/4: Device probing now works with either ACPI, DT, or
> optionally by manually specifying a base, size, and
> register offsets on the command line. This way, all
> architectures offering fw_cfg can be supported, although
> x86 and ARM get *automatic* support via ACPI and/or DT.
>
> HUGE thanks to Laszlo Ersek <lersek-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> for
> pointing out drivers/virtio/virtio_mmio.c, as an example
> on how to pull this off !!!
>
> Stefan: I saw Marc's DMA patches to fw_cfg. Since only
> x86 and ARM will support it starting with QEMU 2.5, and
> since I expect to get lots of otherwise interesting (but
> otherwise orthogonal) feedback on this series, I'd like
> to stick with ioread8() across the board for now. We can
> always patch in DMA support in a backward compatible way
> later, once this series gets (hopefully) accepted :)
>
> Patch 2/4: (was 3/4 in v3): unchanged. Exports kset_find_obj() so
> modules can call it.
>
> Patch 3/4: (was 4/4 in v3): rebased, but otherwise the same.
> Essentially, creates a "human readable" directory
> hierarchy from "path-like" tokens making up fw_cfg
> blob names. I'm not really sure there's a way to make
> this happen via udev rules, but I have at least one
> potential use case for doing it *before* udev becomes
> available (cc: Andy Lutomirski <luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org>),
> so I'd be happy to leave this functionality in the
> kernel module. See further below for an illustration
> of this.
>
> Patch 4/4: Updates the existing ARM DT documentation for fw_cfg,
> mainly by pointing at the more comprehensive document
> introduced with Patch 1/4 for details on the fw_cfg
> device interface, leaving only the specific ARM/DT
> address/size node information in place.
>
>> In addition to the "by_key" blob listing, e.g.:
>>
>> $ tree /sys/firmware/qemu_fw_cfg/
>> /sys/firmware/qemu_fw_cfg/
>> |-- by_key
>> | |-- 32
>> | | |-- key
>> | | |-- name ("etc/boot-fail-wait")
>> | | |-- raw
>> | | `-- size
>> | |-- 33
>> | | |-- key
>> | | |-- name ("etc/smbios/smbios-tables")
>> | | |-- raw
>> | | `-- size
>> | |-- 34
>> | | |-- key
>> | | |-- name ("etc/smbios/smbios-anchor")
>> | | |-- raw
>> | | `-- size
>> | |-- 35
>> | | |-- key
>> | | |-- name ("etc/e820")
>> | | |-- raw
>> | | `-- size
>> | |-- 36
>> | | |-- key
>> | | |-- name ("genroms/kvmvapic.bin")
>> | | |-- raw
>> | | `-- size
>> | |-- 37
>> | | |-- key
>> | | |-- name ("etc/system-states")
>> | | |-- raw
>> | | `-- size
>> | |-- 38
>> | | |-- key
>> | | |-- name ("etc/acpi/tables")
>> | | |-- raw
>> | | `-- size
>> | |-- 39
>> | | |-- key
>> | | |-- name ("etc/table-loader")
>> | | |-- raw
>> | | `-- size
>> | |-- 40
>> | | |-- key
>> | | |-- name ("etc/tpm/log")
>> | | |-- raw
>> | | `-- size
>> | |-- 41
>> | | |-- key
>> | | |-- name ("etc/acpi/rsdp")
>> | | |-- raw
>> | | `-- size
>> | `-- 42
>> | |-- key
>> | |-- name ("bootorder")
>> | |-- raw
>> | `-- size
>> |
>> ...
>>
>> Patch 3/4 also gets us a "human readable" "by_name" listing, like so:
>>
>> ...
>> |-- by_name
>> | |-- bootorder -> ../by_key/42
>> | |-- etc
>> | | |-- acpi
>> | | | |-- rsdp -> ../../../by_key/41
>> | | | `-- tables -> ../../../by_key/38
>> | | |-- boot-fail-wait -> ../../by_key/32
>> | | |-- e820 -> ../../by_key/35
>> | | |-- smbios
>> | | | |-- smbios-anchor -> ../../../by_key/34
>> | | | `-- smbios-tables -> ../../../by_key/33
>> | | |-- system-states -> ../../by_key/37
>> | | |-- table-loader -> ../../by_key/39
>> | | `-- tpm
>> | | `-- log -> ../../../by_key/40
>> | `-- genroms
>> | `-- kvmvapic.bin -> ../../by_key/36
>> `-- rev
>

Gabriel Somlo (4):
firmware: introduce sysfs driver for QEMU's fw_cfg device
kobject: export kset_find_obj() for module use
firmware: create directory hierarchy for sysfs fw_cfg entries
devicetree: update documentation for fw_cfg ARM bindings

.../ABI/testing/sysfs-firmware-qemu_fw_cfg | 100 +++
Documentation/devicetree/bindings/arm/fw-cfg.txt | 38 +-
drivers/firmware/Kconfig | 19 +
drivers/firmware/Makefile | 1 +
drivers/firmware/qemu_fw_cfg.c | 714 +++++++++++++++++++++
lib/kobject.c | 1 +
6 files changed, 837 insertions(+), 36 deletions(-)
create mode 100644 Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg
create mode 100644 drivers/firmware/qemu_fw_cfg.c

--
2.4.3