Libguestfs - Nov 2021 - [PATCH libnbd 0/2] Support concurrent connections using socket activation

Add missing test for socket activation and fix the server socket to use larger
backlog, allowing concurrent connections.

Nir Soffer (2):
  tests: Test nbd_connect_systemd_socket_activation
  socket-activation: Allow multiple connections

 generator/states-connect-socket-activation.c |  2 +-
 tests/Makefile.am                            |  5 ++
 tests/connect-systemd-socket-activation.c    | 83 ++++++++++++++++++++
 3 files changed, 89 insertions(+), 1 deletion(-)
 create mode 100644 tests/connect-systemd-socket-activation.c

-- 
2.31.1

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 at redhat.com>
---
 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

When using qemu-nbd with systemd socket activation, trying to connect
additional clients concurrently fails with:

    nbd_connect_uri: connect: server backlog overflowed, see
    https://bugzilla.redhat.com/1925045: Resource temporarily
    unavailable

But this bug was fixed in qemu-nbd long time ago; turns out that libnbd
has the same bug, creating the server socket with:

    listen(s, 1);

Use SOMAXCONN so we can have multiple connections for better
performance. I think this can be very useful for nbdcopy.

Signed-off-by: Nir Soffer <nsoffer at redhat.com>
---
 generator/states-connect-socket-activation.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/generator/states-connect-socket-activation.c
b/generator/states-connect-socket-activation.c
index 800d963..2abf61b 100644
--- a/generator/states-connect-socket-activation.c
+++ b/generator/states-connect-socket-activation.c
@@ -147,7 +147,7 @@ STATE_MACHINE {
     return 0;
   }
 
-  if (listen (s, 1) == -1) {
+  if (listen (s, SOMAXCONN) == -1) {
     SET_NEXT_STATE (%.DEAD);
     set_error (errno, "listen");
     close (s);
-- 
2.31.1