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Re: [Qemu-devel] The State of the SaveVM format

From: Gerd Hoffmann
Subject: Re: [Qemu-devel] The State of the SaveVM format
Date: Wed, 09 Sep 2009 17:22:11 +0200
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Today, you make no attempt to support older versions even if their
format is quite sane. Take ps2_kbd as an example.

The new format (v3) is:

VMSTATE_STRUCT(common, PS2KbdState, 0, vmstate_ps2_common, PS2State),
VMSTATE_INT32(scan_enabled, PS2KbdState),
VMSTATE_INT32(translate, PS2KbdState),
VMSTATE_INT32_V(scancode_set, PS2KbdState,3),

This is nice and should support v2 and v3.

It doesn't ...

if (version_id == 3)

... setting scancode_set when loading v2 is missing.

I think vmstate fields need a default value to handle cases like this one without having to keep the old load function.

Which has to be an error. But this is the real problem with leaving the
old functions. It encourages sloppiness.

I think we can kill most of the old load functions. I'd keep the old ones only in case emulating the old load function with vmstate would make it unreasonable complex.

static void marshal_pci_irq_levels(void *opaque, const char *name,
size_t offset, int load, int version)
if (version == 2) {
for (i = 0; i < 4; i++)
d->irq_state->piix3->pci_irq_levels[i] = qemu_get_be32(f);

VMSTATE_FUNC_V(irq_state->piix3->pci_irq_levels, PCII440FXState,
marshal_pci_irq_levels, 2)

No. I don't want any free-form C code in vmstate. That will kill quite a few of the vmstate advantages. Imagine a tool dumping snapshot data. What this tool should do when it finds such a FUNC field? It has absolutely no idea what is in there ...


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