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+What: /sys/firmware/memmap/
+Date: June 2008
+Contact: Bernhard Walle <bernhard.walle@gmx.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::
+
+ #!/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