Re: [Libguestfs] [PATCH libnbd 1/2] tests: Test nbd_connect_systemd_socket_activation

I had a think about this. nbd_connect_systemd_socket_activation uses SSA to pass in a listening socket (not a connected socket), so it is expected that the child calls accept(2) at least once on the socket passed in, and presumably anticipated that the child could call accept(2) multiple times. It therefore makes sense that other clients might use the SSA socket. But using nbd_get_uri to obtain this "secret" socket is an unexpected side effect of adding that API. Since it's a listening socket, that rules out future use of socketpair(2) (because that only creates connected sockets, and as far as I can tell there is no way to pass connected sockets through SSA). We might possibly change the implementation in future to use an abstract socket (a Linux extension). Those are in theory expressible as NBD URIs, although it's unlikely that any C library can handle such URIs properly, certainly not libxml2. So I think we can do this as proposed, BUT: - It needs to be documented in the nbd_connect_systemd_socket_activation man page. - Documentation needs to state that if nbd_get_uri() returns NULL or nbd_can_multi_conn() returns <= 0, then multi-conn isn't supported. - Need to also document how to close these shared sockets without deadlocking. I'm still wondering if some kind of nbd_share_systemd_socket_activation() call might be implemented. It would return the "secret" socket path, plus perhaps set a flag on the handle to note that the handle is shared and somehow fix the shutdown path. But I'm not sure how to make that work, and if it's just a more clumsy version of the above. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com Fedora Windows cross-compiler. Compile Windows programs, test, and build Windows installers. Over 100 libraries supported. http://fedoraproject.org/wiki/MinGW