Re: [PATCH for-5.1] qemu-img resize: Require --shrink for shrinking all image formats

[Kevin Wolf <kwolf@redhat.com>]

Am 10.07.2020 um 14:33 hat Peter Maydell geschrieben:
> On Fri, 10 Jul 2020 at 13:17, Kevin Wolf <kwolf@redhat.com> wrote:
> >
> > QEMU 2.11 introduced the --shrink option for qemu-img resize to avoid
> > accidentally shrinking images (commit 4ffca8904a3). However, for
> > compatibility reasons, it was not enforced for raw images yet, but only
> > a deprecation warning was printed. This warning has existed for long
> > enough that we can now finally require --shrink for raw images, too, and
> > error out if it's not given.
> >
> > Documentation already describes the state as it is after this patch.
> >
> > Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> > ---
> >  qemu-img.c | 17 +++--------------
> >  1 file changed, 3 insertions(+), 14 deletions(-)
> >
> > diff --git a/qemu-img.c b/qemu-img.c
> > index e3b2ec3e78..f6a2703039 100644
> > --- a/qemu-img.c
> > +++ b/qemu-img.c
> > @@ -4011,20 +4011,9 @@ static int img_resize(int argc, char **argv)
> >      }
> >
> >      if (total_size < current_size && !shrink) {
> > -        warn_report("Shrinking an image will delete all data beyond the "
> > -                    "shrunken image's end. Before performing such an "
> > -                    "operation, make sure there is no important data there.");
> > -
> > -        if (g_strcmp0(bdrv_get_format_name(blk_bs(blk)), "raw") != 0) {
> > -            error_report(
> > -              "Use the --shrink option to perform a shrink operation.");
> > -            ret = -1;
> > -            goto out;
> > -        } else {
> > -            warn_report("Using the --shrink option will suppress this message. "
> > -                        "Note that future versions of qemu-img may refuse to "
> > -                        "shrink images without this option.");
> > -        }
> > +        error_report("Use the --shrink option to perform a shrink operation.");
> 
> I think it would be nice to retain this bit of text:
> 
> > -        warn_report("Shrinking an image will delete all data beyond the "
> > -                    "shrunken image's end. Before performing such an "
> > -                    "operation, make sure there is no important data there.");
> 
> ie, make the raw-shrink case be the same as the non-raw-shrink
> case currently does.

I had this at first, but then the whole thing looked like a warning and
I wasn't sure that it would still be understood as an error. (Which is
of course a preexisting problem for non-raw.)

Maybe it becomes clearer if I just swap the order and print the error
first and only then the warning?

Kevin