Re: [Qemu-devel] blkdebug and VMDK (iotests 033 failure on monolithicFlat)

[Max Reitz]

On 05.05.2015 12:44, Fam Zheng wrote:
> Max,
>
> Since you once fixed VMDK with the json descriptor filename, could you take a
> look at the error:
>
> $ ./check -vmdk -o "subformat=monolithicFlat" 033
>
> 033         - output mismatch (see 033.out.bad)
> --- /home/fam/qemu/tests/qemu-iotests/033.out   2015-05-05 10:52:50.524378312 
> +0800
> +++ 033.out.bad 2015-05-05 17:38:36.147369924 +0800
> @@ -2,54 +2,36 @@
>   Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728
>   
>   == preparing image ==
> -wrote 1024/1024 bytes at offset 512
> -1 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
> -wrote 1536/1536 bytes at offset 131072
> -1.500 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
> -wrote 131072/131072 bytes at offset 1024
> -128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
> +qemu-io: can't open device blkdebug::/tmp/qemu-iotests/t.vmdk: Cannot use relative extent paths with VMDK descriptor file 'json:{"image": {"driver": 
> "file", "filename": "/tmp/qemu-iotests/t.vmdk"}, "driver": "blkdebug", "align": "512"}'
> +qemu-io: can't open device blkdebug::/tmp/qemu-iotests/t.vmdk: Cannot use relative extent paths with VMDK descriptor file 'json:{"image": {"driver": 
> "file", "filename": "/tmp/qemu-iotests/t.vmdk"}, "driver": "blkdebug", "align": "512"}'
> +qemu-io: can't open device blkdebug::/tmp/qemu-iotests/t.vmdk: Cannot use relative extent paths with VMDK descriptor file 'json:{"image": {"driver": 
> "file", "filename": "/tmp/qemu-iotests/t.vmdk"}, "driver": "blkdebug", "align": "512"}'
>
> ...
>
>
> I'm not sure what's the best fix here. It's possible to dig out
> bs->file->file->filename in this case, but I'm not sure what's the rule of this
> filename mystery.
>
> Fam

Hi Fam,

The problem is that the align option is (consciously) set for blkdebug, 
so the blkdebug driver cannot just convert it to a blkdebug::$foo 
filename, but must create a JSON filename so that the align option is 
included.

I seem to recall that someone (me? I don't know) once proposed a way for 
block drivers not only to present a file name (which is json:{${baz}} in 
this case), but also the name of the directory they are in, or better, a 
template to which a relative path can be appended (in Unix syntax, that 
is, with / as separators and .. and so on). The difference to the file 
name would be that we can ignore all the options given to the block 
driver for controlling its behavior, we just need a path name.

I don't know why we didn't pursue that proposal, but it does seem to be 
necessary here.

I think we can integrate it into the existing bdrv_refresh_filename() 
"infrastructure", so it shouldn't be too difficult. I can take a shot at 
it, if you agree.

Max