Re: [Qemu-devel] [PATCH 09/21] qcow2: Open images with refcount order != 4

[Max Reitz]

On 2014-11-10 at 18:03, Eric Blake wrote:
> On 11/10/2014 06:45 AM, Max Reitz wrote:
> > No longer refuse to open images with a different refcount entry width
> > than 16 bits; only reject images with a refcount width larger than 64
> > bits (which is prohibited by the specification).
> >
> > Signed-off-by: Max Reitz <address@hidden>
> > ---
> >   block/qcow2.c | 8 ++++----
> >   1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/block/qcow2.c b/block/qcow2.c
> > index d70e927..b718e75 100644
> > --- a/block/qcow2.c
> > +++ b/block/qcow2.c
> > @@ -677,10 +677,10 @@ static int qcow2_open(BlockDriverState *bs, QDict 
> > *options, int flags,
> >       }
> >   
> >       /* Check support for various header values */
> > -    if (header.refcount_order != 4) {
> > -        report_unsupported(bs, errp, "%d bit reference counts",
> > -                           1 << header.refcount_order);
> > -        ret = -ENOTSUP;
> > +    if (header.refcount_order > 6) {
> > +        error_setg(errp, "Reference count entry width too large (%i bit); may "
> > +                   "not exceed 64 bit", 1 << header.refcount_order);
> Overflows if I fuzz an image to put 32 or larger into
> header.refcount_order. It may be better to just tweak the error message
> to state that the order cannot exceed 6, rather than trying to display
> the actual bit width that the user is requesting, as then you avoid the
> '1 << problem'.

Yes, probably. Or we display it in binary: "0b1%0*i", 
header.refcount_order, 0 (which works since refcount_order is guaranteed 
to exceed 6).

Joking aside, yes, I'll omit the theoretical refcount width.

Max