From: "Gabriel Somlo" <somlo@cmu.edu> This patch set makes QEMU fw_cfg blobs available for viewing (read-only) via SysFS. Several different architectures supported by QEMU are set up with a "firmware configuration" (fw_cfg) device, used to pass configuration "blobs" into the guest by the host running QEMU. Historically, these config blobs were mostly of interest to the guest BIOS, but since QEMU v2.4 it is possible to insert arbitrary blobs via the command line, which makes them potentially interesting to userspace (e.g. for passing early boot environment variables, etc.). In addition to cc-ing the people and lists indicated by get-maintainer.pl, I've added a few extra lists suggested by Matt Fleming on the qemu-devel list, as well as the qemu-devel list itself. Also cc-ing kernelnewbies, as this is my very first kenel contribution, so please go easy on me for whatever silly n00b mistakes I might have still missed, in spite of trying hard to do all my homework properly... :) The series consists of three patches: 1/3 - probes for the qemu fw_cfg device in locations known to work on the supported architectures, in decreasing order of "likelihood". While it *may* be possible to detect the presence of fw_cfg via acpi or dtb (on x86 and arm, respectively), there's no way I know of attempting that on sun4 and ppc/mac, so I've stuck with simply probing (the fw_cfg_modes[] structure and fw_cfg_io_probe() function) in fw_cfg.c. I could use some advice on how else that could be done more elegantly, if needed. Upon successfully detecting a present fw_cfg device, we set up /sys/firmware/fw_cfg/by_select entries for each blob available on the fw_cfg device. 2/3 - export kset_find_obj() (in lib/kobject.c) for use with modules, which will come in handy in patch #3, below. 3/3 - add a "user friendly" way of listing fw_cfg blobs by name rather than by unique selector key. Since fw_cfg blob names are traditionally set up to look like path names, it would be nice to mirror that fact when displaying them under /sys/firmware/fw_cfg in a "by_name" subdirectory. I'm using ksets to reflect subdirectories matching "dirname" tokens separated by '/' within each fw_cfg blob "filename", and symlinks into the "by_select" subdirectory for each "basename". Since the fw_cfg device doesn't enforce that blob names have well-behaved and non-conflicting names, it is possible (though unlikely) that there will be blobs named: "etc/foo/bar" and "etc/foo" where "foo" will try to be both a subdirectory AND a symlink under /sys/firmware/fw_cfg/by_name/etc/. In such an event, the latter fw_cfg blob will simply be skipped from having an entry created under the user-friendly "by_name" subdirectory, remaining listed only as an entry under the "by_select" subdirectory. I have tested this on x86_64 and armv7hl+lpae kernels. Builds and installs OK as both a module and linked directly into the kernel. TIA for the feedback and advice, --Gabriel Gabriel Somlo (3): firmware: introduce sysfs driver for QEMU's fw_cfg device kobject: export kset_find_obj() to be used from modules firmware: fw_cfg: create directory hierarchy for fw_cfg file names Documentation/ABI/testing/sysfs-firmware-fw_cfg | 211 +++++++++ drivers/firmware/Kconfig | 10 + drivers/firmware/Makefile | 1 + drivers/firmware/fw_cfg.c | 542 ++++++++++++++++++++++++ lib/kobject.c | 1 + 5 files changed, 765 insertions(+) create mode 100644 Documentation/ABI/testing/sysfs-firmware-fw_cfg create mode 100644 drivers/firmware/fw_cfg.c -- 2.4.3