Re: [PATCH v2 for-5.1 9/9] qemu-img: Reject broken -o ""

[Eric Blake <eblake@redhat.com>]

On 4/15/20 2:49 AM, Markus Armbruster wrote:
> qemu-img create, convert, amend, and measure use accumulate_options()
> to merge multiple -o options.  This is broken for -o "":
> 
>      $ qemu-img create -f qcow2 -o backing_file=a -o "" -o backing_fmt=raw,size=1M new.qcow2
>      qemu-img: warning: Could not verify backing image. This may become an error in future versions.
>      Could not open 'a,backing_fmt=raw': No such file or directory
>      Formatting 'new.qcow2', fmt=qcow2 size=1048576 backing_file=a,,backing_fmt=raw cluster_size=65536 lazy_refcounts=off refcount_bits=16
>      $ qemu-img info new.qcow2
>      image: new.qcow2
>      file format: qcow2
>      virtual size: 1 MiB (1048576 bytes)
>      disk size: 196 KiB
>      cluster_size: 65536
> --> backing file: a,backing_fmt=raw
>      Format specific information:
>          compat: 1.1
>          lazy refcounts: false
>          refcount bits: 16
>          corrupt: false
> 
> Merging these three -o the obvious way is wrong, because it results in
> an unwanted ',' escape:
> 
>      backing_file=a,,backing_fmt=raw,size=1M
>                    ~~
> 
> We could silently drop -o "", but Kevin asked me to reject it instead.
> 
> Signed-off-by: Markus Armbruster <armbru@redhat.com>
> ---
>   qemu-img.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)

This results in the error message:
qemu-img: Invalid option list:

with a trailing space and no indication that it was an empty string we 
were trying to warn about.  But that's tolerable.

Reviewed-by: Eric Blake <eblake@redhat.com>

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