[PATCH v3 4/4] qemu-img: Deprecate use of -b without -F

[Kashyap Chamarthy]

On Mon, Mar 09, 2020 at 10:42:25AM -0500, Eric Blake wrote:

[...]

> > > +qemu-img backing file without format (since 5.0.0)
> > > +''''''''''''''''''''''''''''''''''''''''''''''''''
> > > +
> > > +The use of ``qemu-img create``, ``qemu-img rebase``, ``qemu-img
> > > +convert``, or ``qemu-img amend`` to create or modify an image that
> > > +depends on a backing file now recommends that an explicit backing
> > > +format be provided.

Also for the `qemu-img amend` case, I'm not clear if the following scenario
ought to throw the warning:

    $> ~/build/qemu/qemu-img info --backing-chain overlay1.qcow2 
    image: overlay1.qcow2
    file format: qcow2
    virtual size: 4 GiB (4294967296 bytes)
    disk size: 196 KiB
    cluster_size: 65536
    backing file: base.raw
    Format specific information:
        compat: 1.1
        lazy refcounts: false
        refcount bits: 16
        corrupt: false
    
    image: base.raw
    file format: raw
    virtual size: 4 GiB (4294967296 bytes)
    disk size: 778 MiB

    $> ~/build/qemu/qemu-img amend -o compat=v3 overlay1.qcow2 

    $> echo $?
    0

I'm just trying to work out the scenarios where the warnings ought to
show up (for all the four cases: create, rebase, convert, amend).

[...]

-- 
/kashyap