Test connecting using systemd socket activation, and using the handle URI to connect additional handles. The tests reveals a deadlock when closing the first handle owning the nbdkit server. Closing the first handle last avoids this issue. Signed-off-by: Nir Soffer <nsoffer(a)redhat.com&gt; --- tests/Makefile.am | 5 ++ tests/connect-systemd-socket-activation.c | 83 +++++++++++++++++++++++ 2 files changed, 88 insertions(+) create mode 100644 tests/connect-systemd-socket-activation.c diff --git a/tests/Makefile.am b/tests/Makefile.am index 7f00f6f..1451fb8 100644 --- a/tests/Makefile.am +++ b/tests/Makefile.am @@ -192,6 +192,7 @@ check_PROGRAMS += \ opt-list \ opt-info \ opt-list-meta \ + connect-systemd-socket-activation \ connect-unix \ connect-tcp \ connect-tcp6 \ @@ -235,6 +236,7 @@ TESTS += \ opt-list \ opt-info \ opt-list-meta \ + connect-systemd-socket-activation \ connect-unix \ connect-tcp \ connect-tcp6 \ @@ -424,6 +426,9 @@ opt_info_LDADD = $(top_builddir)/lib/libnbd.la opt_list_meta_SOURCES = opt-list-meta.c opt_list_meta_LDADD = $(top_builddir)/lib/libnbd.la +connect_systemd_socket_activation_SOURCES = connect-systemd-socket-activation.c +connect_systemd_socket_activation_LDADD = $(top_builddir)/lib/libnbd.la + connect_unix_SOURCES = connect-unix.c connect_unix_LDADD = $(top_builddir)/lib/libnbd.la diff --git a/tests/connect-systemd-socket-activation.c b/tests/connect-systemd-socket-activation.c new file mode 100644 index 0000000..d64319a --- /dev/null +++ b/tests/connect-systemd-socket-activation.c @@ -0,0 +1,83 @@ +/* NBD client library in userspace + * Copyright (C) 2021 Red Hat Inc. + * + * This library is free software; you can redistribute it and/or + * modify it under the terms of the GNU Lesser General Public + * License as published by the Free Software Foundation; either + * version 2 of the License, or (at your option) any later version. + * + * This library is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + * Lesser General Public License for more details. + * + * You should have received a copy of the GNU Lesser General Public + * License along with this library; if not, write to the Free Software + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA + */ + +/* Test connecting using systemd socket activation. */ + +#include <config.h> + +#include <stdio.h> +#include <stdlib.h> + +#include <libnbd.h> + +#define CONNECTIONS 4 + +int +main (int argc, char *argv[]) +{ + char *args[] = {"nbdkit", "-f", "memory", "size=1m", NULL}; + struct nbd_handle *nbd[CONNECTIONS] = {0}; + char *uri = NULL; + int result = EXIT_FAILURE; + + printf("Connecting handle 0 with systemd socket actication\n"); + + nbd[0] = nbd_create (); + if (nbd[0] == NULL) + goto out; + + if (nbd_connect_systemd_socket_activation (nbd[0], args) == -1) + goto out; + + uri = nbd_get_uri (nbd[0]); + if (uri == NULL) + goto out; + + printf("Using URI: %s\n", uri); + + for (int i = 1; i < CONNECTIONS; i++) { + printf ("Connecting handle %d to URI\n", i); + + nbd[i] = nbd_create (); + if (nbd[i] == NULL) + goto out; + + if (nbd_connect_uri (nbd[i], uri) == -1) + goto out; + } + + printf ("All handles connected\n"); + result = EXIT_SUCCESS; + +out: + if (result == EXIT_FAILURE) + fprintf (stderr, "%s\n", nbd_get_error ()); + + free (uri); + + /* Closing the first connection deadlocks, so we close the additional + * connections first. */ + for (int i = CONNECTIONS - 1; i >= 0; i--) { + if (nbd[i]) { + printf ("Closing handle %d\n", i); + nbd_close (nbd[i]); + } + } + + exit (result); +} -- 2.31.1

On Sun, Nov 07, 2021 at 03:27:46PM +0200, Nir Soffer wrote: The test needs to skip if nbdkit and/or the memory plugin is not available. This can be done using: #include "requires.h" ... requires ("nbdkit --version"); requires ("nbdkit memory --version"); I'm not sure what nbd_get_uri should show here - possibly it *ought* to return NULL (since there's no URI that should connect back to a server launched with systemd-socket-activation). But later ... Now I'm intrigued. I'm guessing the URI exposes the internal socket we create (/tmp/libnbdXXXXXX/sock) for SSA. Which sounds like an "interesting" corner of the API. It also prevents us from changing this in future -- eg. to use socketpair or a socket in the anonymous space. Also this test needs to check for nbd_can_multi_conn >= 1 before actually doing this (although nbdkit will always return it). And this seems like a bear-trap. I support the idea of making this work, but I'm not sure that doing it this way is a good API. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-p2v converts physical machines to virtual machines. Boot with a live CD or over the network (PXE) and turn machines into KVM guests. http://libguestfs.org/virt-v2v

On Sun, Nov 7, 2021 at 3:58 PM Richard W.M. Jones <rjones(a)redhat.com&gt; wrote: Thanks, I'll add it. This is the case: $ tests/connect-systemd-socket-activation Connecting handle 0 with systemd socket activation Using URI: nbd+unix:///?socket=/tmp/libnbd9BNa21/sock Connecting handle 1 to URI Yes we don't document that socket activation uses unix socket, and using this may break in future versions. I think this the user should be in control here. For example: nbd_connect_systemd_socket_activation(h, args, LIBNBD_SA_UNIX) If the user does not care about the type of the socket: nbd_connect_systemd_socket_activation(h, args, LIBNBD_SA_AUTO) Sure, although this is not an example code, just a test. We can cut corners to simplify the test. I suspect this is caused by multiple bugs: - libnbd sends SIGTERM and wait - if the server does not terminate, it will block forever. - nbdkit does not terminate if there are active connections? (I did not investigate yet) So this is not an API issue, just rough edges in libnbd. All this can be done by the user outside of libnbd, but using socket activation in linbd makes this really easy to use.