Re: [Qemu-devel] Failing iotests in CI (was: Add a gitlab-ci file for Continuous Integration testing on Gitlab)

[Kevin Wolf <kwolf@redhat.com>]

Am 19.02.2019 um 13:01 hat Daniel P. Berrangé geschrieben:
> On Tue, Feb 19, 2019 at 12:31:41PM +0100, Kevin Wolf wrote:
> > Am 19.02.2019 um 12:06 hat Daniel P. Berrangé geschrieben:
> > > On Tue, Feb 19, 2019 at 10:37:16AM +0100, Kevin Wolf wrote:
> > > > Am 19.02.2019 um 10:04 hat Thomas Huth geschrieben:
> > > > > 
> > > > >  https://gitlab.com/huth/qemu/-/jobs/163680780
> > > > > 
> > > > > Some of them apparently need encryption to be enabled (as already
> > > > > mentioned by Cleber in his patch) - thus should they really be in the
> > > > > quick check, too? Or could they at least check whether QEMU has been
> > > > > built with encryption?
> > > > 
> > > > The correct solution would be that they detect the situation
> > > > automatically and skip the test by calling _notrun.
> > > > 
> > > > I'm not sure how to detect if a given QEMU binary supports encryption,
> > > > but Dan might know.
> > > 
> > > It isn't easy & depends which encryption feature you're trying to use.
> > > 
> > > For TLS related features you can do something gross like
> > > 
> > >     qemu-img info --object tls-creds-anon,id=dummy README 2>&1
> > >     test $? != 0 && exit 0
> > > 
> > > This relies on fact that 'tls-creds-anon' object type will report a
> > > runtime error during initialization if gnutls isn't enabled.
> > > 
> > > For more general ciphers you pretty much have to just try the higher level
> > > feature and see if it fails.
> > 
> > Actually, I think for test cases we should see 'qemu-img create' failing
> > and could just skip the test if it returns a non-zero exit code.
> > 
> > But then I looked at Thomas' output again:
> > 
> >     --- /builds/huth/qemu/tests/qemu-iotests/188.out	2019-02-19 08:23:54.000000000 +0000
> >     +++ /builds/huth/qemu/tests/qemu-iotests/188.out.bad	2019-02-19 08:34:54.000000000 +0000
> >     @@ -1,4 +1,5 @@
> >      QA output created by 188
> >     +qemu-img: TEST_DIR/t.IMGFMT: No crypto library supporting PBKDF in this build: Function not implemented
> >      Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=16777216 encrypt.format=luks encrypt.key-secret=sec0 encrypt.iter-time=10
> > 
> >      == reading whole image ==--- /builds/huth/qemu/tests/qemu-iotests/188.out	2019-02-19 08:23:54.000000000 +0000
> > 
> > What is it actually doing there? There's clearly an error message, but
> > it almost looks like it's creating some kind of image anyway? The
> > following I/O works fine (i.e. this created image can even be opened
> > again with the luks driver), except that you can also access the image
> > with the wrong password.
> > 
> > Is this a real bug in either qcow2 or luks?
> 
> It is an artifact of the way qcow2 image creation happens in multiple
> phases. qcow2_co_create first creates a minimal qcow2 file, and then
> opens it and updates it to add in the various extra features, including
> luks encryption. We fail to create the luks encryption, but enough of
> the qcow2 file has been created that it is able to still do plain text
> I/O.

But why doesn't qcow2_update_options_prepare() fail then? If you pass
encryption options like 188 does, but the image isn't encrypted, then
the function at least attempts to error out. Where is this failing?

> Essentially the problem is that qcow2_co_create() doesn't unlink() the
> partially created image when things fail. This is a generic problem
> which can affect any part of qcow2_co_create that might fail, but it
> is especially problematic with luks.
> 
> The complication in fixing this is that can't just do an unlink() as
> we can't assume a local file. We need to have a bdrv_unlink() driver
> callback we can use to delegate to the right block driver APIs for
> deletion.

.bdrv_co_create can't unlink at all, because that would be undoing
something that it didn't even do itself. If I created a file (local or
on a remote server that is accessed over a network protocol) and my
blockdev-create command to create the qcow2 layer fails, I certainly
don't expect the resource that I manually created to go away.

What .bdrv_co_create could and probably should do is make the header
invalid so that it's still recognised as qcow2 (to avoid probing it as
raw), but opening it fails.

> This is something I think could be useful in general, to expose as a
> "qemu-img delete" command - especially for non-local formats like
> rbd, sheepdog, glusterfs the mgmt app can't simply run "rm $img".
> QEMU already knows how to talk to the native APis for these network
> drivers so can make life easier by exposing a 'delete' op.
> 
> For luks it would be desirable to allow options to the 'delete'
> operation, for example to request scrubbing of the key material
> headers.

This could still be useful, just not necessarily in the context of
blockdev-create. It could actually be used in 'qemu-img create', which
creates both the protocol layer and the format layer.

Kevin