Re: [PATCH 2/2] qemu-iotests: Test convert to qcow2 compressed to NBD

[Eric Blake]

On 7/27/20 9:35 AM, Nir Soffer wrote:

> > I guess it's okay that you don't create a real tar file here, but
> > listing the commands to create it (even as a comment) is better than
> > just saying "trust me".  And it doesn't seem like that much more work -
> > it looks like the key to your test is that you created a tar file
> > containing two files, where the first file was less than 512 bytes and
> > the second file is your target destination that you will be rewriting.
>
> The real code is more complicated, something like:
>
>      offset = tar.fileobj.tell() + BLOCK_SIZE
>
>      with open(tar.name, "r+") as f:
>          f.truncate(offset + measure["required"])
>
>      convert_image(image, tar.name, offset)
>
>      check = check_image(tar.name, offset)
>      size = check["image-end-offset"]
>
>      member = tarfile.TarInfo(name)
>      member.size = size
>      tar.addfile(member)
>
>      tar_size = offset + round_up(size)
>
>      tar.fileobj.seek(tar_size)
>      with open(tar.name, "r+") as f:
>          f.truncate(tar_size)
>
> I'm not sure it helps qemu developers working on these tests.

The closer the iotest is to reality, the more likely it will serve as a 
good regression test.  Cutting corners risks a test that passes in 
isolation even when we've done something that breaks the overall process 
in one of the corners you cut.


> > At any rate, given the urgency of getting pull requests for -rc2 in
> > before slamming Peter tomorrow, I'll probably try to touch up the issues
> > Max pointed out and queue it today.
>
> Thanks Max and Eric.
>
> Should I post a fixed version later today?

A v2 would be helpful.

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org