[Libguestfs] [PATCH nbdkit 4/4] New filter: limit: Limit number of clients that can connect.
Richard W.M. Jones
rjones at redhat.com
Wed Mar 4 15:17:26 UTC 2020
---
filters/limit/nbdkit-limit-filter.pod | 61 ++++++++++++++
configure.ac | 2 +
filters/limit/Makefile.am | 60 ++++++++++++++
tests/Makefile.am | 3 +
filters/limit/limit.c | 115 ++++++++++++++++++++++++++
tests/test-limit.sh | 81 ++++++++++++++++++
TODO | 2 -
7 files changed, 322 insertions(+), 2 deletions(-)
diff --git a/filters/limit/nbdkit-limit-filter.pod b/filters/limit/nbdkit-limit-filter.pod
new file mode 100644
index 00000000..e334decb
--- /dev/null
+++ b/filters/limit/nbdkit-limit-filter.pod
@@ -0,0 +1,61 @@
+=head1 NAME
+
+nbdkit-limit-filter - limit number of clients that can connect
+
+=head1 SYNOPSIS
+
+ nbdkit --filter=limit PLUGIN [limit=N]
+
+=head1 DESCRIPTION
+
+C<nbdkit-limit-filter> is an nbdkit filter that limits the number of
+clients which can connect concurrently. If more than C<limit=N>
+(default: 1) clients try to connect at the same time then later
+clients are rejected.
+
+=head1 PARAMETERS
+
+=over 4
+
+=item B<limit=>N
+
+Limit the number of concurrent clients to C<N>. This parameter is
+optional. If not specified then the limit defaults to 1. You can
+also set this to 0 to make the number of clients unlimited (ie.
+disable the filter).
+
+=back
+
+=head1 FILES
+
+=over 4
+
+=item F<$filterdir/nbdkit-limit-filter.so>
+
+The filter.
+
+Use C<nbdkit --dump-config> to find the location of C<$filterdir>.
+
+=back
+
+=head1 VERSION
+
+C<nbdkit-limit-filter> first appeared in nbdkit 1.20.
+
+=head1 SEE ALSO
+
+L<nbdkit(1)>,
+L<nbdkit-exitlast-filter(1)>,
+L<nbdkit-ip-filter(1)>,
+L<nbdkit-noparallel-filter(1)>,
+L<nbdkit-rate-filter(1)>,
+L<nbdkit-filter(3)>,
+L<nbdkit-plugin(3)>.
+
+=head1 AUTHORS
+
+Richard W.M. Jones
+
+=head1 COPYRIGHT
+
+Copyright (C) 2020 Red Hat Inc.
diff --git a/configure.ac b/configure.ac
index 0b980238..2db4b546 100644
--- a/configure.ac
+++ b/configure.ac
@@ -102,6 +102,7 @@ filters="\
extentlist \
fua \
ip \
+ limit \
log \
nocache \
noextents \
@@ -1029,6 +1030,7 @@ AC_CONFIG_FILES([Makefile
filters/extentlist/Makefile
filters/fua/Makefile
filters/ip/Makefile
+ filters/limit/Makefile
filters/log/Makefile
filters/nocache/Makefile
filters/noextents/Makefile
diff --git a/filters/limit/Makefile.am b/filters/limit/Makefile.am
new file mode 100644
index 00000000..75704082
--- /dev/null
+++ b/filters/limit/Makefile.am
@@ -0,0 +1,60 @@
+# nbdkit
+# Copyright (C) 2019-2020 Red Hat Inc.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+# * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#
+# * Redistributions in binary form must reproduce the above copyright
+# notice, this list of conditions and the following disclaimer in the
+# documentation and/or other materials provided with the distribution.
+#
+# * Neither the name of Red Hat nor the names of its contributors may be
+# used to endorse or promote products derived from this software without
+# specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND
+# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+# THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
+# PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
+# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
+# USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+# ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+# OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+# OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+# SUCH DAMAGE.
+
+include $(top_srcdir)/common-rules.mk
+
+EXTRA_DIST = nbdkit-limit-filter.pod
+
+filter_LTLIBRARIES = nbdkit-limit-filter.la
+
+nbdkit_limit_filter_la_SOURCES = \
+ limit.c \
+ $(top_srcdir)/include/nbdkit-filter.h \
+ $(NULL)
+
+nbdkit_limit_filter_la_CPPFLAGS = -I$(top_srcdir)/include
+nbdkit_limit_filter_la_CFLAGS = $(WARNINGS_CFLAGS)
+nbdkit_limit_filter_la_LDFLAGS = \
+ -module -avoid-version -shared \
+ -Wl,--version-script=$(top_srcdir)/filters/filters.syms \
+ $(NULL)
+
+if HAVE_POD
+
+man_MANS = nbdkit-limit-filter.1
+CLEANFILES += $(man_MANS)
+
+nbdkit-limit-filter.1: nbdkit-limit-filter.pod
+ $(PODWRAPPER) --section=1 --man $@ \
+ --html $(top_builddir)/html/$@.html \
+ $<
+
+endif HAVE_POD
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 2ac8fb31..324339c1 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -1064,6 +1064,9 @@ TESTS += test-fua.sh
# ip filter test.
TESTS += test-ip-filter.sh
+# limit filter test.
+TESTS += test-limit.sh
+
# log filter test.
TESTS += test-log.sh
diff --git a/filters/limit/limit.c b/filters/limit/limit.c
new file mode 100644
index 00000000..c7308e9c
--- /dev/null
+++ b/filters/limit/limit.c
@@ -0,0 +1,115 @@
+/* nbdkit
+ * Copyright (C) 2019-2020 Red Hat Inc.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ * * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * * Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ *
+ * * Neither the name of Red Hat nor the names of its contributors may be
+ * used to endorse or promote products derived from this software without
+ * specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
+ * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
+ * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <config.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <nbdkit-filter.h>
+
+#ifdef HAVE_STDATOMIC_H
+#include <stdatomic.h>
+#else
+/* Some old platforms lack atomic types, but 32 bit ints are usually
+ * "atomic enough".
+ */
+#define _Atomic /**/
+#endif
+
+/* Counts client connections. */
+static _Atomic unsigned connections;
+
+/* Client limit (0 = filter is disabled). */
+static unsigned limit = 1;
+
+static int
+limit_config (nbdkit_next_config *next, nbdkit_backend *nxdata,
+ const char *key, const char *value)
+{
+ if (strcmp (key, "limit") == 0) {
+ if (nbdkit_parse_unsigned ("limit", value, &limit) == -1)
+ return -1;
+ return 0;
+ }
+
+ return next (nxdata, key, value);
+}
+
+/* We limit connections in the preconnect stage (in particular before
+ * any heavyweight NBD or TLS negotiations has been done). However we
+ * count connections in the open/close calls since clients can drop
+ * out between preconnect and open.
+ */
+static int
+limit_preconnect (nbdkit_next_preconnect *next, nbdkit_backend *nxdata,
+ int readonly)
+{
+ if (next (nxdata, readonly) == -1)
+ return -1;
+
+ if (limit == 0 || connections < limit)
+ return 0;
+
+ nbdkit_error ("limit: too many clients connected, connection rejected");
+ return -1;
+}
+
+static void *
+limit_open (nbdkit_next_open *next, nbdkit_backend *nxdata,
+ int readonly)
+{
+ if (next (nxdata, readonly) == -1)
+ return NULL;
+
+ connections++;
+
+ return NBDKIT_HANDLE_NOT_NEEDED;
+}
+
+static void
+limit_close (void *handle)
+{
+ --connections;
+}
+
+static struct nbdkit_filter filter = {
+ .name = "limit",
+ .longname = "nbdkit limit filter",
+ .config = limit_config,
+ .preconnect = limit_preconnect,
+ .open = limit_open,
+ .close = limit_close,
+};
+
+NBDKIT_REGISTER_FILTER(filter)
diff --git a/tests/test-limit.sh b/tests/test-limit.sh
new file mode 100755
index 00000000..aa7c2b19
--- /dev/null
+++ b/tests/test-limit.sh
@@ -0,0 +1,81 @@
+#!/usr/bin/env bash
+# nbdkit
+# Copyright (C) 2019-2020 Red Hat Inc.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+# * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#
+# * Redistributions in binary form must reproduce the above copyright
+# notice, this list of conditions and the following disclaimer in the
+# documentation and/or other materials provided with the distribution.
+#
+# * Neither the name of Red Hat nor the names of its contributors may be
+# used to endorse or promote products derived from this software without
+# specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND
+# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+# THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
+# PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
+# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
+# USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+# ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+# OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+# OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+# SUCH DAMAGE.
+
+source ./functions.sh
+set -e
+set -x
+
+requires nbdsh --version
+
+sock=`mktemp -u`
+files="limit.pid $sock"
+cleanup_fn rm -f $files
+
+# Start nbdkit with the limit filter and a limit of 2 clients.
+start_nbdkit -P limit.pid -U $sock --filter=limit memory size=1M limit=2
+
+export sock
+
+nbdsh -c - <<'EOF'
+import os
+import sys
+import time
+
+sock = os.environ["sock"]
+
+# It should be possible to connect two clients.
+# Note that nbdsh creates the ‘h’ handle implicitly.
+h.connect_unix (sock)
+h2 = nbd.NBD ()
+h2.connect_unix (sock)
+
+# A third connection is expected to fail.
+try:
+ h3 = nbd.NBD ()
+ h3.connect_unix (sock)
+ # This should not happen.
+ sys.exit (1)
+except nbd.Error:
+ pass
+
+# Close one of the existing connections.
+del h2
+
+# There's a possible race between closing the client socket
+# and nbdkit noticing and closing the connection.
+time.sleep (5)
+
+# Now a new connection should be possible.
+h4 = nbd.NBD ()
+h4.connect_unix (sock)
+
+EOF
diff --git a/TODO b/TODO
index cd2e47a5..e094c332 100644
--- a/TODO
+++ b/TODO
@@ -10,8 +10,6 @@ General ideas for improvements
sizes and threads, as that should make it easier to identify
systematic issues.
-* Limit number of incoming connections (like qemu-nbd -e).
-
* For parallel plugins, only create threads on demand from parallel
client requests, rather than pre-creating all threads at connection
time, up to the thread pool size limit. Of course, once created, a
--
2.25.0
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