Re: [Qemu-block] [Qemu-devel] [PATCH 2/2] qcow2: mark image as corrupt if failing during create

[Eric Blake]

On 2/19/19 6:50 AM, Daniel P. Berrangé wrote:
> During creation we write a minimal qcow2 header and then update it with
> extra features. If the updating fails for some reason we might still be
> left with a valid qcow2 image that will be mistakenly used for I/O. We
> cannot delete the image, since we don't know if we created the
> underlying storage or not. Thus we mark the header as corrupt to
> prevents its later usage.

Should we unconditionally mark the image as corrupt at the time we write
the minimal qcow2 header, and then update the image to non-corrupt on
the final update?

> 
> Signed-off-by: Daniel P. Berrangé <address@hidden>
> ---
>  block/qcow2.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/block/qcow2.c b/block/qcow2.c
> index ecc577175f..338513e652 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -3104,6 +3104,9 @@ qcow2_co_create(BlockdevCreateOptions *create_options, 
> Error **errp)
>  
>      ret = 0;
>  out:
> +    if (ret < 0) {
> +        qcow2_mark_corrupt(blk_bs(blk));
> +    }

If ret < 0 because of an EIO error, this may also fail to write the
change to the header. Hence my question as to whether this is too late.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org