[Qemu-devel] Re: [PATCH] add VMSTATE_BOOL

[Michael S. Tsirkin]

On Tue, Nov 09, 2010 at 02:28:37PM +0100, Gerd Hoffmann wrote:
> On 11/09/10 14:05, Michael S. Tsirkin wrote:
> >On Tue, Nov 09, 2010 at 12:50:11PM +0100, Gerd Hoffmann wrote:
> >>   Hi,
> >>
> >>>>>>+static int get_bool(QEMUFile *f, void *pv, size_t size)
> >>>>>>+{
> >>>>>>+    bool *v = pv;
> >>>>>>+    *v = qemu_get_byte(f);
> >>>>>>+    return 0;
> >>
> >>>I think we should verify that value is 0 or 1 and fail
> >>>migration otherwise, to make it more robust.
> >>
> >>I still think such a check doesn't belong into the migration code as
> >>such a bug would exist without migration too.  And if anything we
> >>should check on save not on load, otherwise qemu can write out
> >>savevm images which it will refuse to load.  I wouldn't call this
> >>"robust".
> >>
> >>cheers,
> >>   Gerd
> >
> >I think we should verify on load: e.g. the image could have
> >got corrupted.
> 
> For catching corruption checksums work much better.

Unless there's a bug in software that writes the file, then checksum
will match.

> >What, exactly, do you want to check on save?
> 
> I don't want to check anything.

Why did you suggest it above then?

> I'm just saying that *if* we are sanity-checking bool

My patch doesn't check bool. Look at it. I am sanity
checking a byte read from file. File can have any values,
there is no guarantee that it has the same value
that the same version of qemu wrote out.

> to catch bugs
> it is much more useful to do that when saving.

There's nothing we *can* check.
        if (v == true || v == false)
is always true according to the language standard.
How is it useful to stick always true conditions that compiler
will likely remove in code?

> >savevm: validate bool values on load
> >
> >We always save 0 or 1 values for booleans.  Validate on input to
> >increase the chance of detecting input corruption.
> 
> NACK.
> 
> cheers,
>   Gerd