[Qemu-devel] [PATCH v2 0/3] Migration-safe ACPI table sizing algorithm

[Paolo Bonzini <pbonzini@redhat.com>]

In the emergency last-minute patches of QEMU 2.1 we did two things:

- fixed migration problems from 1.7 or 2.0 to 2.1 due to changes in
  ACPI table sizes

- ensured that future versions will not break migration compatibility
  with 2.2 for reasonable configurations (with ACPI tables smaller
  than a hundred kilobytes, roughly)

However, this came at the cost of wasting 128 KB unconditionally on
even the smaller configuration, and we didn't provide a mechanism to
ensure compatibility with larger configurations.

This series provides this mechanism.  As mentioned early, the design
is to consider the SSDT immutable and versioned (together with other
non-AML tables such as HPET, TPMA and MADT, SRAT, MCFG, DMAR).
The DSDT instead can change more or less arbitrarily.  To do this,
we add padding after the DSDT to allow for future growth (patch 1).

Once we do this, the size of the ACPI table fw_cfg "file" is constant
given a machine type and a command-line, so we do not need anymore the
larger 128KB padding (patch 2).

Patch 3 is just cleanups.

Paolo

v1->v2: drop linuxboot changes, instead modify the option ROM
        in a separate patch

Paolo Bonzini (3):
  pc: introduce new ACPI table sizing algorithm
  pc: go back to smaller ACPI tables
  pc: clean up pre-2.1 compatibility code

 hw/i386/acpi-build.c | 20 +++++++++++---------
 hw/i386/pc_piix.c    | 20 +++++++++++++++++++-
 hw/i386/pc_q35.c     |  6 ++++--
 include/hw/i386/pc.h |  2 ++
 4 files changed, 36 insertions(+), 12 deletions(-)

-- 
2.1.0