Re: [Qemu-block] [PATCH v2 13/13] qemu-iotests: Test the x-blockdev-reopen QMP command

[Alberto Garcia]

On Sat 13 Apr 2019 02:53:42 AM CEST, Max Reitz wrote:
>> Calling x-blockdev-reopen without 'backing' should only fail if
>> 
>>  a) the image has a backing file attached to it.
>>     In this case it doesn't: we just detached it in the previous line.
>> 
>>  b) there's a default backing file written on the image header.
>>     In this case there isn't (hd0 is created without one in setUp()).
>
> That’s what I thought, too, hence me applying effectively the same
> change to the test in v4 of my series as you in your "Fix check for
> default backing files" series:
>
> http://lists.nongnu.org/archive/html/qemu-block/2019-04/msg00308.html
>
>> So it should not fail. I think the bug is that the test for condition
>> (b) in bdrv_reopen_prepare() that returns "backing is missing..." is
>> using backing_file but it should use (correct me if I'm wrong)
>> auto_backing_file.
>
> Well, I think both should be fine, because...

Why would both be fine? backing_file refers to the backing file
currently attached, and auto_backing_file refers to the one written on
the image metadata, or am I wrong?

>> Not directly related to this, but should bdrv_backing_detach() also
>> clear backing_file ?
>
> ...I don’t think it should.  That’s what that my patch addresses. The
> real problem is that bs->backing_file is not a cache for
> bs->backing->bs->filename, so it shouldn’t be treated as such.

But what's the point of having backing_file set if no backing file is
attached?

Berto