sysfs: add /sys/firmware/memmap

This patch adds /sys/firmware/memmap interface that represents the BIOS
(or Firmware) provided memory map. The tree looks like:

    /sys/firmware/memmap/0/start   (hex number)
                           end     (hex number)
                           type    (string)
    ...                 /1/start
                           end
                           type

With the following shell snippet one can print the memory map in the same form
the kernel prints itself when booting on x86 (the E820 map).

  --------- 8< --------------------------
    #!/bin/sh
    cd /sys/firmware/memmap
    for dir in * ; do
        start=$(cat $dir/start)
        end=$(cat $dir/end)
        type=$(cat $dir/type)
        printf "%016x-%016x (%s)\n" $start $[ $end +1] "$type"
    done
  --------- >8 --------------------------

That patch only provides the needed interface:

 1. The sysfs interface.
 2. The structure and enumeration definition.
 3. The function firmware_map_add() and firmware_map_add_early()
    that should be called from architecture code (E820/EFI, for
    example) to add the contents to the interface.

If the kernel is compiled without CONFIG_FIRMWARE_MEMMAP, the interface does
nothing without cluttering the architecture-specific code with #ifdef's.

The purpose of the new interface is kexec: While /proc/iomem represents
the *used* memory map (e.g. modified via kernel parameters like 'memmap'
and 'mem'), the /sys/firmware/memmap tree represents the unmodified memory
map provided via the firmware. So kexec can:

 - use the original memory map for rebooting,
 - use the /proc/iomem for setting up the ELF core headers for kdump
   case that should only represent the memory of the system.

The patch has been tested on i386 and x86_64.

Signed-off-by: Bernhard Walle <bwalle@suse.de>
Acked-by: Greg KH <gregkh@suse.de>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Cc: kexec@lists.infradead.org
Cc: yhlu.kernel@gmail.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 10 insertions, 0 deletions

diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
index dc2cec6127d1..ebb9e51deb0c 100644
--- a/drivers/firmware/Kconfig
+++ b/drivers/firmware/Kconfig
@@ -26,6 +26,16 @@ config EDD_OFF
           kernel. Say N if you want EDD enabled by default. EDD can be dynamically set
           using the kernel parameter 'edd={on|skipmbr|off}'.
 
+config FIRMWARE_MEMMAP
+    bool "Add firmware-provided memory map to sysfs" if EMBEDDED
+    default (X86_64 || X86_32)
+    help
+      Add the firmware-provided (unmodified) memory map to /sys/firmware/memmap.
+      That memory map is used for example by kexec to set up parameter area
+      for the next kernel, but can also be used for debugging purposes.
+
+      See also Documentation/ABI/testing/sysfs-firmware-memmap.
+
 config EFI_VARS
         tristate "EFI Variable Support via sysfs"
         depends on EFI