Re: [Qemu-devel] [PATCH for-2.10 3/3] qemu-img/convert: Move bs_n > 1 && -B check down

[Max Reitz <mreitz@redhat.com>]

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On 13.04.2017 23:17, Eric Blake wrote:
> On 04/13/2017 03:34 PM, Max Reitz wrote:
>> It does not make much sense to use a backing image for the target when
>> you concatenate multiple images (because then there is no correspondence
>> between the source images' backing files and the target's); but it was
>> still possible to give one by using -o backing_file=X instead of -B X.
>>
>> Fix this by moving the check.
>>
>> (Also, change the error message because -B is not the only way to
>>  specify the backing file, evidently.)
> 
> For that matter, 'create -B' is intentionally? undocumented in the
> qemu-img --help and man page.  (Personally, I don't know why we don't
> want it documented - is it because it it not a universal option because
> not all formats support backing files?)

(I suppose you mean convert instead of create)

Well, the man page at least documents that you can use backing_file for
the destination and what it will do. So documenting would probably be
just "Oh, you can also use -B, by the way."

I won't promise to write a patch to fix that, but I do hope I will. :-)

>> Cc: qemu-stable <qemu-stable@nongnu.org>
>> Signed-off-by: Max Reitz <mreitz@redhat.com>
>> ---
>>  qemu-img.c                 | 14 +++++++-------
>>  tests/qemu-iotests/122.out |  4 ++--
>>  2 files changed, 9 insertions(+), 9 deletions(-)
>>
> 
> Reviewed-by: Eric Blake <eblake@redhat.com>

Thanks, as always!

Max

> Having a backing file for the destination may still make sense for some
> convoluted workflow, but you can get that with a followup qemu-img rebase.


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