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>

Documentation/ABI/testing/sysfs-firmware-memmap

@@ -0,0 +1,71 @@
+What:		/sys/firmware/memmap/
+Date:		June 2008
+Contact:	Bernhard Walle <bwalle@suse.de>
+Description:
+		On all platforms, the firmware provides a memory map which the
+		kernel reads. The resources from that memory map are registered
+		in the kernel resource tree and exposed to userspace via
+		/proc/iomem (together with other resources).
+
+		However, on most architectures that firmware-provided memory
+		map is modified afterwards by the kernel itself, either because
+		the kernel merges that memory map with other information or
+		just because the user overwrites that memory map via command
+		line.
+
+		kexec needs the raw firmware-provided memory map to setup the
+		parameter segment of the kernel that should be booted with
+		kexec. Also, the raw memory map is useful for debugging. For
+		that reason, /sys/firmware/memmap is an interface that provides
+		the raw memory map to userspace.
+
+		The structure is as follows: Under /sys/firmware/memmap there
+		are subdirectories with the number of the entry as their name:
+
+			/sys/firmware/memmap/0
+			/sys/firmware/memmap/1
+			/sys/firmware/memmap/2
+			/sys/firmware/memmap/3
+			...
+
+		The maximum depends on the number of memory map entries provided
+		by the firmware. The order is just the order that the firmware
+		provides.
+
+		Each directory contains three files:
+
+		start	: The start address (as hexadecimal number with the
+			  '0x' prefix).
+		end	: The end address, inclusive (regardless whether the
+			  firmware provides inclusive or exclusive ranges).
+		type	: Type of the entry as string. See below for a list of
+			  valid types.
+
+		So, for example:
+
+			/sys/firmware/memmap/0/start
+			/sys/firmware/memmap/0/end
+			/sys/firmware/memmap/0/type
+			/sys/firmware/memmap/1/start
+			...
+
+		Currently following types exist:
+
+		  - System RAM
+		  - ACPI Tables
+		  - ACPI Non-volatile Storage
+		  - reserved
+
+		Following shell snippet can be used to display that memory
+		map in a human-readable format:
+
+		-------------------- 8< ----------------------------------------
+		  #!/bin/bash
+		  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 ----------------------------------------