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

From: Max Reitz
Subject: Re: [Qemu-devel] [PATCH for-2.10 3/3] qemu-img/convert: Move bs_n > 1 && -B check down
Date: Wed, 19 Apr 2017 14:38:36 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.0

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 <address@hidden>
>> Signed-off-by: Max Reitz <address@hidden>
>> ---
>>  qemu-img.c                 | 14 +++++++-------
>>  tests/qemu-iotests/122.out |  4 ++--
>>  2 files changed, 9 insertions(+), 9 deletions(-)
> Reviewed-by: Eric Blake <address@hidden>

Thanks, as always!


> 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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