The /dev/acpi character device gives an aperture into physical memory
that allows only read access to known ACPI tables: RSDP, XSDT/RSDT, and
the root tables. Adapt acpidump(8) to use this interface by default,
falling back to the old /dev/mem method if it is not available or if
ACPIDUMP_USE_DEVMEM=1 is set in the environment. The user visible benefit
of this change is that "options INSECURE" is no longer required to
dump ACPI tables.
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