Re: [Qemu-devel] [PATCH] qemu-img: allow rebase to a NULL backing file when unsafe

[Kevin Wolf]

Am 13.04.2011 16:51, schrieb Stefan Hajnoczi:
> From: Anthony Liguori <address@hidden>
> 
> QEMU can drop a backing file so that an image file no longer depends on
> the backing file, but this feature has not been exposed in qemu-img.
> This is useful in an image streaming usecase or when an image file has
> been fully allocated and no reads can hit the backing file anymore.
> 
> Since the dropping the backing file can make the image unusable, only
> allow this when the unsafe flag has been set.

I think it would also make sense to allow it in safe mode, it would have
the same effect as rebasing onto an empty new backing file. Might take
more than a one-liner, though.

In case you need a workaround for older qemu-img versions, -b "" works,
too (at least for qcow2).

> Signed-off-by: Anthony Liguori <address@hidden>
> Signed-off-by: Stefan Hajnoczi <address@hidden>
> ---
>  qemu-img.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/qemu-img.c b/qemu-img.c
> index d9c2c12..ed5ba91 100644
> --- a/qemu-img.c
> +++ b/qemu-img.c
> @@ -1240,7 +1240,7 @@ static int img_rebase(int argc, char **argv)
>          }
>      }
>  
> -    if ((optind >= argc) || !out_baseimg) {
> +    if ((optind >= argc) || (!unsafe && !out_baseimg)) {
>          help();
>      }
>      filename = argv[optind++];

Thanks, applied to the block branch.

Kevin