Re: [Qemu-devel] [PATCH 0/4] target-sparc: Update to use VMStateDescription

[Mark Cave-Ayland]

On 10/08/15 13:34, Peter Maydell wrote:

> This patchset updates target-sparc to use VMStateDescription
> rather than hand-written save/load functions. (This and CRIS
> are the last two targets still using the old approach.)
> 
> It's based on some patches from back in 2012 by Juan which
> I've updated, rebased and made some tweaks to.
> 
> This is a migration compatibility break; we don't care about
> cross-version migration on SPARC guests, and not having to
> maintain the old wire format allows a cleaner vmstate
> description in several ways.
> 
> NB that the 'split cpu_put_psr' patch seems to me to be a
> bugfix in and of itself, since currently we might try to
> call cpu_check_irqs() and deliver interrupts while we're
> halfway through updating a PSR value...
> 
> Juan Quintela (2):
>   vmstate: introduce CPU_DoubleU arrays
>   target-sparc: Convert to VMStateDescription
> 
> Peter Maydell (2):
>   target-sparc: Split cpu_put_psr into side-effect and no-side-effect
>     parts
>   target-sparc: Don't flush TLB in cpu_load function
> 
>  hw/sparc64/sun4u.c          |  20 ---
>  include/migration/vmstate.h |   7 +
>  migration/vmstate.c         |  23 +++
>  target-sparc/cpu-qom.h      |   4 +
>  target-sparc/cpu.c          |   1 +
>  target-sparc/cpu.h          |   7 +-
>  target-sparc/machine.c      | 360 
> ++++++++++++++++++++------------------------
>  target-sparc/win_helper.c   |  19 ++-
>  8 files changed, 210 insertions(+), 231 deletions(-)

Hi Peter,

Thanks for looking into this! In general the patches look very
reasonable (although I will need to give them a more thorough testing
when I get a chance) - my only concern is the break in migration
compatibility. Am I right in thinking that with this patch applied a
loadvm cannot restore a savevm from an earlier version?

Not so much for qemu-system-sparc64 which is still somewhat
experimental, however qemu-system-sparc has become very usable since
2012 with the advent of the cg3 and OpenBIOS changes that can now run
Solaris/SunOS and I do have a slight concern that people could lose
their qcow2 snapshots. Then again if we document this loudly in the
release notes then I guess it is possible to convert a snapshot back to
a raw, boot that and then savevm it back to the newer qcow2 again...


ATB,

Mark.