Re: [PATCH] qemu-img: Unify [-b [-F]] documentation

[Kevin Wolf <kwolf@redhat.com>]

Am 31.01.2022 um 14:59 hat Hanna Reitz geschrieben:
> qemu-img convert documents the backing file and backing format options
> as follows:
>     [-B backing_file [-F backing_fmt]]
> whereas qemu-img create has this:
>     [-b backing_file] [-F backing_fmt]
> 
> That is, for convert, we document that -F cannot be given without -B,
> while for create, way say that they are independent.
> 
> Indeed, it is technically possible to give -F without -b, because it is
> left to the block driver to decide whether this is an error or not, so
> sometimes it is:
> 
> $ qemu-img create -f qed -F qed test.qed 64M
> Formatting 'test.qed', fmt=qed size=67108864 backing_fmt=qed [...]
> 
> And sometimes it is not:
> 
> $ qemu-img create -f qcow2 -F qcow2 test.qcow2 64M
> Formatting 'test.qcow2', fmt=qcow2 cluster_size=65536 [...]
> qemu-img: test.qcow2: Backing format cannot be used without backing file
> 
> Generally, it does not make much sense, though, and users should only
> give -F with -b, so document it that way, as we have already done for
> qemu-img convert (commit 1899bf47375ad40555dcdff12ba49b4b8b82df38).
> 
> Reported-by: Tingting Mao <timao@redhat.com>
> Signed-off-by: Hanna Reitz <hreitz@redhat.com>

Thanks, applied to the block branch.

Kevin