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

[Richard W.M. Jones]

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.

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:

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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