Re: [Qemu-devel] [PATCH] qemu-img: add the simplest format recognition

[Eric Blake <eblake@redhat.com>]

On 12/01/2017 02:05 PM, Klim Kireev wrote:
> Now, if you type something like
> 
> qemu-img create disk.qcow2 1G
> or
> qemu-img dd if=/dev/sda of=disk.qcow2
> 
> it creates a raw image and if you need you should
> manually specify an image format with -f qcow2. It would
> be more convenient if it could be detected from an extension.
> 
> This patch adds a simple heuristic to recognize the image format
> for qcow, qcow2, vmdk, vhdx, vdi
> 
> Signed-off-by: Klim Kireev <klim.kireev@virtuozzo.com>
> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>   qemu-img.c | 24 ++++++++++++++++++++++--
>   1 file changed, 22 insertions(+), 2 deletions(-)

Is it also worth warning the user that we guessed, and that they should 
specify -f if our guess was wrong?

> @@ -496,6 +510,9 @@ static int img_create(int argc, char **argv)
>   
>       /* Get the filename */
>       filename = (optind < argc) ? argv[optind] : NULL;
> +    if (fmt == NULL) {
> +        fmt = get_format(filename);

Particularly if fmt == "raw", because the user typed something like 
'foo.img' instead of 'foo.qcow2'. I suspect another common mis-guess 
would be users that type .qcow but want qcow2.

The idea makes sense to me, though.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org