[Qemu-devel] [PATCH v6 0/4] SysFS driver for QEMU fw_cfg device

[Gabriel L. Somlo]

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 v5:

        - fixed typos in documentation files (Patches 1/4 and 4/4

        - printf/scanf type modifier for phys_addr_t now matches
          arch-specific width (u32 vs. u64), avoiding compiler warnings.
          (tested on i386 with and without PAE, and on armv7hl with and
           without lpae -- the latter pair took quite a while on an
           emulated QEMU guest :) )

Thanks,
  --Gabriel

>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.
>
>>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 <address@hidden> 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 <address@hidden>),
>>                 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                     | 735 +++++++++++++++++++++
 lib/kobject.c                                      |   1 +
 6 files changed, 858 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