x86: Export x86 boot_params to sysfs

kexec-tools use boot_params for getting the 1st kernel hardware_subarch,
the kexec kernel EFI runtime support also needs to read the old efi_info
from boot_params. Currently it exists in debugfs which is not a good
place for such infomation. Per HPA, we should avoid "sploit debugfs".

In this patch /sys/kernel/boot_params are exported, also the setup_data is
exported as a subdirectory. kexec-tools is using debugfs for hardware_subarch
for a long time now so we're not removing it yet.

Structure is like below:

/sys/kernel/boot_params
|__ data                /* boot_params in binary*/
|__ setup_data
|   |__ 0               /* the first setup_data node */
|   |   |__ data        /* setup_data node 0 in binary*/
|   |   |__ type        /* setup_data type of setup_data node 0, hex string */
[snip]
|__ version             /* boot protocal version (in hex, "0x" prefixed)*/

Signed-off-by: Dave Young <dyoung@redhat.com>
Acked-by: Borislav Petkov <bp@suse.de>
Tested-by: Toshi Kani <toshi.kani@hp.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>

1 files changed, 38 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-kernel-boot_params b/Documentation/ABI/testing/sysfs-kernel-boot_params
new file mode 100644
index 000000000000..eca38ce2852d
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-kernel-boot_params
@@ -0,0 +1,38 @@
+What:           /sys/kernel/boot_params
+Date:           December 2013
+Contact:        Dave Young <dyoung@redhat.com>
+Description:    The /sys/kernel/boot_params directory contains two
+                files: "data" and "version" and one subdirectory "setup_data".
+                It is used to export the kernel boot parameters of an x86
+                platform to userspace for kexec and debugging purpose.
+
+                If there's no setup_data in boot_params the subdirectory will
+                not be created.
+
+                "data" file is the binary representation of struct boot_params.
+
+                "version" file is the string representation of boot
+                protocol version.
+
+                "setup_data" subdirectory contains the setup_data data
+                structure in boot_params. setup_data is maintained in kernel
+                as a link list. In "setup_data" subdirectory there's one
+                subdirectory for each link list node named with the number
+                of the list nodes. The list node subdirectory contains two
+                files "type" and "data". "type" file is the string
+                representation of setup_data type. "data" file is the binary
+                representation of setup_data payload.
+
+                The whole boot_params directory structure is like below:
+                /sys/kernel/boot_params
+                |__ data
+                |__ setup_data
+                |   |__ 0
+                |   |   |__ data
+                |   |   |__ type
+                |   |__ 1
+                |       |__ data
+                |       |__ type
+                |__ version
+
+Users:          Kexec