Re: [PATCH v3 2/4] iotests: Switch nbd tests to use Unix rather than TCP

[Eric Blake]

On 11/18/19 11:42 AM, Eric Blake wrote:

> > > +++ b/tests/qemu-iotests/common.filter
> > > @@ -127,7 +127,8 @@ _filter_img_create()
> > >           -e "s#$TEST_DIR#TEST_DIR#g" \
> > >           -e "s#$SOCK_DIR#SOCK_DIR#g" \
> > >           -e "s#$IMGFMT#IMGFMT#g" \
> > > -        -e 's#nbd:127.0.0.1:10810#TEST_DIR/t.IMGFMT#g' \
> > > +        -e 's#nbd:127.0.0.1:[0-9]\\+#TEST_DIR/t.IMGFMT#g' \
> > > +        -e 's#nbd+unix:///\??socket=SOCK_DIR/nbd#TEST_DIR/t.IMGFMT#g' \
> >
> > Why the second question mark?  I thought the ? after the /// was 
> > mandatory.
>
> Some of our code outputs:
>
> nbd+unix://?socket=...
>
> when there is no export name, while other outputs:
>
> nbd+unix:///?socket=...

Re-reading 
https://github.com/NetworkBlockDevice/nbd/blob/master/doc/uri.md and RFC 
3986, I see that both forms appear to be valid URIs (both have empty 
authority, the first has empty path and the second has path '/', but NBD 
says leading / in path is stripped to form the export name).  However, 
the NBD document does not mention the 2-slash form with no URI authority 
or export name; perhaps we should amend that document to make it obvious 
that it is indeed valid.

> When there IS an export name, it outputs
>
> nbd+unix:///name?socket=...

While in this case, the 3-slash form is essential - with only two 
slashes, the URI 'nbd+unix://name?socket' would be trying to access a 
URI authority of 'name' with an empty path, rather than the intended 
empty authority and path of '/name' which gets translated to the NBD 
export 'name'.

> So the regex is matching 2 or 3 / (using \? to make the third optional), 
> then a mandatory ?.

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