[libvirt] [PATCH] util: storagefile: Properly set transport type when parsing NBD strings

[Peter Krempa]

On Thu, Jan 16, 2020 at 13:13:38 +0000, Richard W.M. Jones wrote:
> On Thu, Jan 16, 2020 at 12:41:37PM +0100, Peter Krempa wrote:
> > When parsing legacy NBD backing file strings such as
> > 'nbd:unix:/tmp/sock:exportname=/' we'd fail to set the transport to
> > VIR_STORAGE_NET_HOST_TRANS_UNIX. This started to be a problem once we
> > actually started to generate config of the backing store on the command
> > line with -blockdev as the JSON code would try to format it as TCP and
> > fail with:
> > 
> >  internal error: argument key 'host' must not have null value
> > 
> > Set the type properly and add a test.
> > 
> > This bug was found by the libguestfs test suite in:
> > 
> > https://bugzilla.redhat.com/show_bug.cgi?id=1791614
> 
> The bug was found by Ming Xie of the virt-v2v QE team.

I'll add a

Reported-by: Ming Xie <mxie at redhat.com>

> 
> The patch itself looks fine as far as I can tell.  But I'm having real
> problems actually testing it.  Can you suggest any way to test libvirt
> parsing these URIs?
> 
> My current method (which doesn't work for reasons that I don't
> understand) is:
> 
> (1) Compile libvirt from source.
> 
> (2) Run ./run src/libvirtd &
> 
> (3) Create an NBD server + overlay file:
> 
> rm /tmp/sock
> nbdkit -U /tmp/sock memory 1G
> qemu-img create -f qcow2 overlay.qcow2 -b nbd:unix:/tmp/sock:exportname=/ -F raw
> 
> (4) Try to boot a libvirt guest using the overlay:
> 
> virt-install --import --name test --disk path=overlay.qcow2,format=raw --memory 1024
> 
> But for some reason libvirt just ignores the overlay:

Do you also use qemu-4.2? The bug manifests itself only when -blockdev
is used. That's why it was dormant at least since 2014. I did not bother
looking further into the history.

At any rate, if it's inconvenient to install qemu-4.2 you can
force-enable blockdev for testing using:

<domain type='kvm' xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'>
   ...
   <qemu:capabilities>
     <qemu:add capability='blockdev'/>
   </qemu:capabilities>
</domain>



> 
> 2020-01-16 13:00:44.980+0000: 2378711: warning : virStorageBackendVolOpen:1527 : ignoring missing file 'nbd:unix:/tmp/sock'
> 
> I verified that the overlay works in programs like qemu-img so it
> doesn't seem to be a problem with the overlay itself.
> 
> Rich.
> 
> > Signed-off-by: Peter Krempa <pkrempa at redhat.com>
> > ---
> >  src/util/virstoragefile.c | 2 +-
> >  tests/virstoragetest.c    | 4 ++++
> >  2 files changed, 5 insertions(+), 1 deletion(-)
> > 
> > diff --git a/src/util/virstoragefile.c b/src/util/virstoragefile.c
> > index 1397f532fd..7a2af0ad94 100644
> > --- a/src/util/virstoragefile.c
> > +++ b/src/util/virstoragefile.c
> > @@ -2964,7 +2964,7 @@ virStorageSourceParseNBDColonString(const char *nbdstr,
> >          }
> > 
> >          src->hosts->socket = g_strdup(backing[2]);
> > -
> > +        src->hosts->transport = VIR_STORAGE_NET_HOST_TRANS_UNIX;
> >     } else {
> >          src->hosts->name = g_strdup(backing[1]);
> > 
> > diff --git a/tests/virstoragetest.c b/tests/virstoragetest.c
> > index 2862758752..370e19252b 100644
> > --- a/tests/virstoragetest.c
> > +++ b/tests/virstoragetest.c
> > @@ -1258,6 +1258,10 @@ mymain(void)
> >                         "<source protocol='nbd' name=':test'>\n"
> >                         "  <host name='example.org' port='6000'/>\n"
> >                         "</source>\n");
> > +    TEST_BACKING_PARSE("nbd:unix:/tmp/sock:exportname=/",
> > +                       "<source protocol='nbd' name='/'>\n"
> > +                       "  <host transport='unix' socket='/tmp/sock'/>\n"
> > +                       "</source>\n");
> >      TEST_BACKING_PARSE("nbd://example.org:1234",
> >                         "<source protocol='nbd'>\n"
> >                         "  <host name='example.org' port='1234'/>\n"
> > -- 
> > 2.24.1
> > 
> > --
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