What: /sys/firmware/memmap/
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Date: June 2008
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Contact: Bernhard Walle <bernhard.walle@gmx.de>
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Description:
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On all platforms, the firmware provides a memory map which the
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kernel reads. The resources from that memory map are registered
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in the kernel resource tree and exposed to userspace via
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/proc/iomem (together with other resources).
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However, on most architectures that firmware-provided memory
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map is modified afterwards by the kernel itself, either because
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the kernel merges that memory map with other information or
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just because the user overwrites that memory map via command
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line.
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kexec needs the raw firmware-provided memory map to setup the
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parameter segment of the kernel that should be booted with
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kexec. Also, the raw memory map is useful for debugging. For
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that reason, /sys/firmware/memmap is an interface that provides
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the raw memory map to userspace.
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The structure is as follows: Under /sys/firmware/memmap there
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are subdirectories with the number of the entry as their name::
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/sys/firmware/memmap/0
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/sys/firmware/memmap/1
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/sys/firmware/memmap/2
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/sys/firmware/memmap/3
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...
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The maximum depends on the number of memory map entries provided
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by the firmware. The order is just the order that the firmware
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provides.
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Each directory contains three files:
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======== =====================================================
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start The start address (as hexadecimal number with the
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'0x' prefix).
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end The end address, inclusive (regardless whether the
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firmware provides inclusive or exclusive ranges).
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type Type of the entry as string. See below for a list of
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valid types.
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======== =====================================================
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So, for example::
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/sys/firmware/memmap/0/start
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/sys/firmware/memmap/0/end
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/sys/firmware/memmap/0/type
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/sys/firmware/memmap/1/start
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...
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Currently following types exist:
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- System RAM
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- ACPI Tables
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- ACPI Non-volatile Storage
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- reserved
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Following shell snippet can be used to display that memory
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map in a human-readable format::
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#!/bin/bash
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cd /sys/firmware/memmap
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for dir in * ; do
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start=$(cat $dir/start)
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end=$(cat $dir/end)
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type=$(cat $dir/type)
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printf "%016x-%016x (%s)\n" $start $[ $end +1] "$type"
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done
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