[Qemu-devel] [PATCH v4 0/4] SysFS driver for QEMU fw_cfg device

["Gabriel L. Somlo" <somlo@cmu.edu>]

From: "Gabriel Somlo" <somlo@cmu.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/...

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@redhat.com> 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@amacapital.net>),
		   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.

Thanks much,
  --Gabriel

>  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         | 240 +++++++
 Documentation/devicetree/bindings/arm/fw-cfg.txt   |  37 +-
 drivers/firmware/Kconfig                           |  19 +
 drivers/firmware/Makefile                          |   1 +
 drivers/firmware/qemu_fw_cfg.c                     | 714 +++++++++++++++++++++
 lib/kobject.c                                      |   1 +
 6 files changed, 977 insertions(+), 35 deletions(-)
 create mode 100644 Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg
 create mode 100644 drivers/firmware/qemu_fw_cfg.c

-- 
2.4.3