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

[Peter Maydell <peter.maydell@linaro.org>]

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.

thanks
-- PMM