On 2012-08-29 09:05, Pavel Dovgaluk wrote: >> -----Original Message----- >> From: Jan Kiszka [mailto:jan.kis...@web.de] >> Sent: Tuesday, August 28, 2012 11:13 AM >> To: Pavel Dovgaluk >> Cc: 'qemu-devel' >> Subject: Re: [PATCH] Save/load PC speaker internal state (v2) >> >> On 2012-08-28 08:58, Pavel Dovgaluk wrote: >>> Save PC speaker state to remove differences between system >>> states after saving the snapshot and after loading it again. >>> This patch is needed for deterministic replay of the execution. >>> >>> v2: Do not save the data that cannot affect the guest code behavior. >>> >>> Signed-off-by: Pavel Dovgalyuk<pavel.dovga...@gmail.com> >>> --- >>> hw/pcspk.c | 17 +++++++++++++++-- >>> 1 files changed, 15 insertions(+), 2 deletions(-) >>> >>> diff --git a/hw/pcspk.c b/hw/pcspk.c >>> index e430324..07a3de0 100644 >>> --- a/hw/pcspk.c >>> +++ b/hw/pcspk.c >>> @@ -46,8 +46,8 @@ typedef struct { >>> unsigned int pit_count; >>> unsigned int samples; >>> unsigned int play_pos; >>> - int data_on; >>> - int dummy_refresh_clock; >>> + uint8_t data_on; >>> + uint8_t dummy_refresh_clock; >>> } PCSpkState; >>> >>> static const char *s_spk = "pcspk"; >>> @@ -159,6 +159,18 @@ static const MemoryRegionOps pcspk_io_ops = { >>> }, >>> }; >>> >>> +static const VMStateDescription vmstate_spk = { >>> + .name = "pcspk", >>> + .version_id = 1, >>> + .minimum_version_id = 1, >>> + .minimum_version_id_old = 1, >>> + .fields = (VMStateField[]) { >>> + VMSTATE_UINT8(data_on, PCSpkState), >>> + VMSTATE_UINT8(dummy_refresh_clock, PCSpkState), >> >> Just to understand the plan: The intention is to leave the audio >> disabled after resume, just saving those bits that can be read back via >> IO port, correct? Then please document this in a comment, otherwise fix it. > > The plan is to make guest system behavior deterministic. > Resuming the audio is not needed for this but could be a useful side effect. > I thought about solutions of this problem and got the following: > we cannot reinitialize the buffer in post_load function, because pit used for > samples generation could be not reloaded yet at that moment and the buffer's > state > will be invalid in this case. > So the only solution is saving and loading the complete state of the audio > buffer.
Theoretically, you could save the required PIT state inside the pcspk VMSD to solve this (still less bytes than saving the buffer). However, I see no relevant loss in leaving audio off until the guest fiddles with the controls again. I'm just asking for documenting this. Jan
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