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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
- Unusable memory
- Persistent Memory (legacy)
- Persistent Memory
- Soft Reserved
- 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
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