Re: [PATCH v3 06/17] hw/sd/sdcard: Do not store vendor data on block drive (CMD56)

[Peter Xu <peterx@redhat.com>]

On Tue, Jul 09, 2024 at 05:38:54PM -0300, Fabiano Rosas wrote:
> Philippe Mathieu-Daudé <philmd@linaro.org> writes:
> 
> > "General command" (GEN_CMD, CMD56) is described as:
> >
> >   GEN_CMD is the same as the single block read or write
> >   commands (CMD24 or CMD17). The difference is that [...]
> >   the data block is not a memory payload data but has a
> >   vendor specific format and meaning.
> >
> > Thus this block must not be stored overwriting data block
> > on underlying storage drive. Keep it in a dedicated
> > 'vendor_data[]' array.
> >
> > Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> > Tested-by: Cédric Le Goater <clg@redhat.com>
> > ---
> > RFC: Is it safe to reuse VMSTATE_UNUSED_V() (which happens
> > to be the same size)?
> 
> Hi, sorry it took some time to get to this, I had just left for vacation
> when you first posted.

And I totally overlooked there's the email.. until you replied.  Welcome
back.

> 
> I think it's ok:
> 
> {
>   "field": "unused",
>   "version_id": 1,
>   "field_exists": false,
>   "size": 512
> },
> 
> vs.
> 
> {
>   "field": "vendor_data",
>   "version_id": 0,
>   "field_exists": false,
>   "num": 512,
>   "size": 1
> },
> 
> The unused field was introduced in 2016 so there's no chance of
> migrating a QEMU that old to/from 9.1.

What happens if an old qemu 9.0 sends rubbish here to a new QEMU, while the
new QEMU would consider it meaningful data?

-- 
Peter Xu