According to the NBD spec, a server advertising
NBD_FLAG_CAN_MULTI_CONN promises that multiple client connections will
not see any cache inconsistencies: when properly separated by a single
flush, actions performed by one client will be visible to another
client, regardless of which client did the flush. We satisfy these
conditions in qemu when our block layer is backed by the local
filesystem (by virtue of the semantics of fdatasync(), and the fact
that qemu itself is not buffering writes beyond flushes). It is
harder to state whether we satisfy these conditions for network-based
protocols, so the safest course of action is to allow users to opt-in
to advertising multi-conn. We may later tweak defaults to advertise
by default when the block layer can confirm that the underlying
protocol driver is cache consistent between multiple writers, but for
now, this at least allows savvy users (such as virt-v2v or nbdcopy) to
explicitly start qemu-nbd or qemu-storage-daemon with multi-conn
advertisement in a known-safe setup where the client end can then
benefit from parallel clients.
It makes sense, and will be used by oVirt. Actually we are already using
multiple connections for writing about 2 years, based on your promise
that if every client writes to district areas this is safe.
Note, however, that we don't want to advertise MULTI_CONN when we know
that a second client cannot connect (for historical reasons, qemu-nbd
defaults to a single connection while nbd-server-add and QMP commands
default to unlimited connections; but we already have existing means
to let either style of NBD server creation alter those defaults). The
harder part of this patch is setting up an iotest to demonstrate
behavior of multiple NBD clients to a single server. It might be
possible with parallel qemu-io processes, but concisely managing that
in shell is painful. I found it easier to do by relying on the libnbd
project's nbdsh, which means this test will be skipped on platforms
where that is not available.
Signed-off-by: Eric Blake <eblake@redhat.com>
Fixes: https://bugzilla.redhat.com/1708300
---
v1 was in Aug 2021 [1], with further replies in Sep [2] and Oct [3].
[1] https://lists.gnu.org/archive/html/qemu-devel/2021-08/msg04900.html
[2] https://lists.gnu.org/archive/html/qemu-devel/2021-09/msg00038.html
[3] https://lists.gnu.org/archive/html/qemu-devel/2021-10/msg06744.html
Since then, I've tweaked the QAPI to mention 7.0 (instead of 6.2), and
reworked the logic so that default behavior is unchanged for now
(advertising multi-conn on a writable export requires opt-in during
the command line or QMP, but remains default for a readonly export).
I've also expanded the amount of testing done in the new iotest.
docs/interop/nbd.txt | 1 +
docs/tools/qemu-nbd.rst | 3 +-
qapi/block-export.json | 34 +++-
include/block/nbd.h | 3 +-
blockdev-nbd.c | 5 +
nbd/server.c | 27 ++-
MAINTAINERS | 1 +
tests/qemu-iotests/tests/nbd-multiconn | 188 +++++++++++++++++++++
tests/qemu-iotests/tests/nbd-multiconn.out | 112 ++++++++++++
9 files changed, 363 insertions(+), 11 deletions(-)
create mode 100755 tests/qemu-iotests/tests/nbd-multiconn
create mode 100644 tests/qemu-iotests/tests/nbd-multiconn.out
diff --git a/docs/interop/nbd.txt b/docs/interop/nbd.txt
index bdb0f2a41aca..6c99070b99c8 100644
--- a/docs/interop/nbd.txt
+++ b/docs/interop/nbd.txt
@@ -68,3 +68,4 @@ NBD_CMD_BLOCK_STATUS for "qemu:dirty-bitmap:", NBD_CMD_CACHE
* 4.2: NBD_FLAG_CAN_MULTI_CONN for shareable read-only exports,
NBD_CMD_FLAG_FAST_ZERO
* 5.2: NBD_CMD_BLOCK_STATUS for "qemu:allocation-depth"
+* 7.0: NBD_FLAG_CAN_MULTI_CONN for shareable writable exports
diff --git a/docs/tools/qemu-nbd.rst b/docs/tools/qemu-nbd.rst
index 6031f9689312..1de785524c36 100644
--- a/docs/tools/qemu-nbd.rst
+++ b/docs/tools/qemu-nbd.rst
@@ -139,8 +139,7 @@ driver options if ``--image-opts`` is specified.
.. option:: -e, --shared=NUM
Allow up to *NUM* clients to share the device (default
- ``1``), 0 for unlimited. Safe for readers, but for now,
- consistency is not guaranteed between multiple writers.
+ ``1``), 0 for unlimited.
Removing the note means that now consistency is guaranteed between
multiple writers, no?
Or maybe we want to mention here that consistency depends on the protocol
and users can opt in, or refer to the section where this is discussed?
.. option:: -t, --persistent
diff --git a/qapi/block-export.json b/qapi/block-export.json
index f183522d0d2c..0a27e8ee84f9 100644
--- a/qapi/block-export.json
+++ b/qapi/block-export.json
@@ -21,7 +21,9 @@
# recreated on the fly while the NBD server is active.
# If missing, it will default to denying access (since 4.0).
# @max-connections: The maximum number of connections to allow at the same
-# time, 0 for unlimited. (since 5.2; default: 0)
+# time, 0 for unlimited. Setting this to 1 also stops
+# the server from advertising multiple client support
+# (since 5.2; default: 0)
#
# Since: 4.2
##
@@ -50,7 +52,9 @@
# recreated on the fly while the NBD server is active.
# If missing, it will default to denying access (since 4.0).
# @max-connections: The maximum number of connections to allow at the same
-# time, 0 for unlimited. (since 5.2; default: 0)
+# time, 0 for unlimited. Setting this to 1 also stops
+# the server from advertising multiple client support
+# (since 5.2; default: 0).
#
# Returns: error if the server is already running.
#
@@ -79,6 +83,26 @@
{ 'struct': 'BlockExportOptionsNbdBase',
'data': { '*name': 'str', '*description': 'str' } }
+##
+# @NbdExportMultiConn:
+#
+# Possible settings for advertising NBD multiple client support.
+#
+# @off: Do not advertise multiple clients.
+#
+# @on: Allow multiple clients (for writable clients, this is only safe
+# if the underlying BDS is cache-consistent, such as when backed
+# by the raw file driver); ignored if the NBD server was set up
+# with max-connections of 1.
+#
+# @auto: Behaves like @off if the export is writable, and @on if the
+# export is read-only.
+#
+# Since: 7.0
+##
+{ 'enum': 'NbdExportMultiConn',
+ 'data': ['off', 'on', 'auto'] }
Are we going to have --multi-con=(on|off|auto)?
+
##
# @BlockExportOptionsNbd:
#
@@ -95,11 +119,15 @@
# the metadata context name "qemu:allocation-depth" to
# inspect allocation details. (since 5.2)
#
+# @multi-conn: Controls whether multiple client support is advertised, if the
+# server's max-connections is not 1. (default auto, since 7.0)
+#
# Since: 5.2
##
{ 'struct': 'BlockExportOptionsNbd',
'base': 'BlockExportOptionsNbdBase',
- 'data': { '*bitmaps': ['str'], '*allocation-depth': 'bool' } }
+ 'data': { '*bitmaps': ['str'], '*allocation-depth': 'bool',
+ '*multi-conn': 'NbdExportMultiConn' } }
##
# @BlockExportOptionsVhostUserBlk:
diff --git a/include/block/nbd.h b/include/block/nbd.h
index 78d101b77488..138b9857dbcb 100644
--- a/include/block/nbd.h
+++ b/include/block/nbd.h
@@ -1,5 +1,5 @@
/*
- * Copyright (C) 2016-2020 Red Hat, Inc.
+ * Copyright (C) 2016-2022 Red Hat, Inc.
* Copyright (C) 2005 Anthony Liguori <anthony@codemonkey.ws>
*
* Network Block Device
@@ -346,6 +346,7 @@ void nbd_client_put(NBDClient *client);
void nbd_server_is_qemu_nbd(bool value);
bool nbd_server_is_running(void);
+int nbd_server_max_connections(void);
void nbd_server_start(SocketAddress *addr, const char *tls_creds,
const char *tls_authz, uint32_t max_connections,
Error **errp);
diff --git a/blockdev-nbd.c b/blockdev-nbd.c
index bdfa7ed3a5a9..0df222e868d8 100644
--- a/blockdev-nbd.c
+++ b/blockdev-nbd.c
@@ -44,6 +44,11 @@ bool nbd_server_is_running(void)
return nbd_server || is_qemu_nbd;
}
+int nbd_server_max_connections(void)
+{
+ return nbd_server ? nbd_server->max_connections : -1;
+}
-1 is a little bit strange for a limit, maybe 1 is a better default when
we nbd_server == NULL? When can this happen?
+
static void nbd_blockdev_client_closed(NBDClient *client, bool ignored)
{
nbd_client_put(client);
diff --git a/nbd/server.c b/nbd/server.c
index 9fb2f264023e..f17aacc8139f 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -1,5 +1,5 @@
/*
- * Copyright (C) 2016-2021 Red Hat, Inc.
+ * Copyright (C) 2016-2022 Red Hat, Inc.
* Copyright (C) 2005 Anthony Liguori <anthony@codemonkey.ws>
*
* Network Block Device Server Side
@@ -1641,7 +1641,7 @@ static int nbd_export_create(BlockExport *blk_exp, BlockExportOptions *exp_args,
int64_t size;
uint64_t perm, shared_perm;
bool readonly = !exp_args->writable;
- bool shared = !exp_args->writable;
+ bool multi_conn;
strList *bitmaps;
size_t i;
int ret;
@@ -1679,6 +1679,23 @@ static int nbd_export_create(BlockExport *blk_exp, BlockExportOptions *exp_args,
return size;
}
+ /*
+ * Determine whether to advertise multi-conn. Default is auto,
+ * which resolves to on for read-only and off for writable. But
+ * if the server has max-connections 1, that forces the flag off.
Looks good, this can be enabled automatically based on the driver
if we want, so users using auto will can upgrade to multi-con automatically.
+ */
+ if (!arg->has_multi_conn) {
+ arg->multi_conn = NBD_EXPORT_MULTI_CONN_AUTO;
+ }
+ if (nbd_server_max_connections() == 1) {
+ arg->multi_conn = NBD_EXPORT_MULTI_CONN_OFF;
+ }
+ if (arg->multi_conn == NBD_EXPORT_MULTI_CONN_AUTO) {
+ multi_conn = readonly;
+ } else {
+ multi_conn = arg->multi_conn == NBD_EXPORT_MULTI_CONN_ON;
+ }
This part is a little bit confusing - we do:
- initialize args->multi_con if it has not value
- set the temporary multi_con based now initialized args->multi_con
I think it will be nicer to separate arguments parsing, so there is no need
to initialize it here or have arg->has_multi_conn, but I did not check how
other arguments are handled.
+
/* Don't allow resize while the NBD server is running, otherwise we don't
* care what happens with the node. */
blk_get_perm(blk, &perm, &shared_perm);
@@ -1692,11 +1709,11 @@ static int nbd_export_create(BlockExport *blk_exp, BlockExportOptions *exp_args,
exp->description = g_strdup(arg->description);
exp->nbdflags = (NBD_FLAG_HAS_FLAGS | NBD_FLAG_SEND_FLUSH |
NBD_FLAG_SEND_FUA | NBD_FLAG_SEND_CACHE);
+ if (multi_conn) {
+ exp->nbdflags |= NBD_FLAG_CAN_MULTI_CONN;
+ }
if (readonly) {
exp->nbdflags |= NBD_FLAG_READ_ONLY;
- if (shared) {
- exp->nbdflags |= NBD_FLAG_CAN_MULTI_CONN;
- }
} else {
exp->nbdflags |= (NBD_FLAG_SEND_TRIM | NBD_FLAG_SEND_WRITE_ZEROES |
NBD_FLAG_SEND_FAST_ZERO);v
diff --git a/MAINTAINERS b/MAINTAINERS
index 9814580975c5..24dd800ae3f8 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -3334,6 +3334,7 @@ F: qemu-nbd.*
F: blockdev-nbd.c
F: docs/interop/nbd.txt
F: docs/tools/qemu-nbd.rst
+F: tests/qemu-iotests/tests/*nbd*
T: git https://repo.or.cz/qemu/ericb.git nbd
T: git https://src.openvz.org/scm/~vsementsov/qemu.git nbd
diff --git a/tests/qemu-iotests/tests/nbd-multiconn b/tests/qemu-iotests/tests/nbd-multiconn
new file mode 100755
index 000000000000..0261552f32f2
--- /dev/null
+++ b/tests/qemu-iotests/tests/nbd-multiconn
@@ -0,0 +1,188 @@
+#!/usr/bin/env bash
+# group: rw auto quick
+#
+# Test that qemu-nbd MULTI_CONN works
+#
+# Copyright (C) 2018-2022 Red Hat, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program 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 General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program. If not, see <http://www.gnu.org/licenses/>.
+#
+
+seq="$(basename $0)"
+echo "QA output created by $seq"
+
+status=1 # failure is the default!
+
+_cleanup()
+{
+ _cleanup_test_img
+ _cleanup_qemu
+ rm -f "$SOCK_DIR/nbd"
+}
+trap "_cleanup; exit \$status" 0 1 2 3 15
+
+# get standard environment, filters and checks
+cd ..
+. ./common.rc
+. ./common.filter
+. ./common.qemu
+. ./common.nbd
+
+_supported_fmt qcow2
+_supported_proto file
+_supported_os Linux
+_require_command QEMU_NBD
+
+# Parallel client connections are easier with libnbd than qemu-io:
+if ! (nbdsh --version) >/dev/null 2>&1; then
+ _notrun "nbdsh utility required, skipped this test"
+fi
+
+echo
+echo "=== Initial image setup ==="
+echo
+
+_make_test_img 4M
+$QEMU_IO -c 'w -P 1 0 2M' -c 'w -P 2 2M 2M' "$TEST_IMG" | _filter_qemu_io
+_launch_qemu 2> >(_filter_nbd)
+_send_qemu_cmd $QEMU_HANDLE '{"execute":"qmp_capabilities"}' "return"
+_send_qemu_cmd $QEMU_HANDLE '{"execute":"blockdev-add",
+ "arguments":{"driver":"qcow2", "node-name":"n",
+ "file":{"driver":"file", "filename":"'"$TEST_IMG"'"}}}' "return"
+export nbd_unix_socket
+
+echo
+echo "=== Default nbd server settings ==="
+echo
+# Default allows for unlimited connections, readonly images advertise
+# multi-conn, and writable images do not
+_send_qemu_cmd $QEMU_HANDLE '{"execute":"nbd-server-start",
+ "arguments":{"addr":{"type":"unix",
+ "data":{"path":"'"$nbd_unix_socket"'"}}}}' "return"
+_send_qemu_cmd $QEMU_HANDLE '{"execute":"block-export-add",
+ "arguments":{"type":"nbd", "id":"r", "node-name":"n",
+ "name":"r"}}' "return"
+_send_qemu_cmd $QEMU_HANDLE '{"execute":"block-export-add",
+ "arguments":{"type":"nbd", "id":"w", "node-name":"n",
+ "name":"w", "writable":true}}' "return"
+nbdsh -u "nbd+unix:///r?socket=$nbd_unix_socket" -c '
+assert h.can_multi_conn()
+h.shutdown()
+print("nbdsh passed")'
+nbdsh -u "nbd+unix:///w?socket=$nbd_unix_socket" -c '
+assert not h.can_multi_conn()
+h.shutdown()
+print("nbdsh passed")'
Mixing of shell and python is very confusing. Wouldn't it be much cleaner
to write the test in python?
+_send_qemu_cmd $QEMU_HANDLE '{"execute":"block-export-del",
+ "arguments":{"id":"r"}}' "DELETED"
+_send_qemu_cmd $QEMU_HANDLE '{"execute":"block-export-del",
+ "arguments":{"id":"w"}}' "DELETED"
+
+echo
+echo "=== Per-export overrides of defaults ==="
+echo
+# Can explicitly disable multi-conn for readonly image, and explicitly
+# enable it for writable image
+_send_qemu_cmd $QEMU_HANDLE '{"execute":"block-export-add",
+ "arguments":{"type":"nbd", "id":"r", "node-name":"n",
+ "name":"r", "multi-conn":"off"}}' "return"
+_send_qemu_cmd $QEMU_HANDLE '{"execute":"block-export-add",
+ "arguments":{"type":"nbd", "id":"w", "node-name":"n",
+ "name":"w", "multi-conn":"on", "writable":true}}' "return"
+nbdsh -u "nbd+unix:///r?socket=$nbd_unix_socket" -c '
+assert not h.can_multi_conn()
+h.shutdown()
+print("nbdsh passed")'
+nbdsh -u "nbd+unix:///w?socket=$nbd_unix_socket" -c '
+assert h.can_multi_conn()
+h.shutdown()
+print("nbdsh passed")'
+_send_qemu_cmd $QEMU_HANDLE '{"execute":"block-export-del",
+ "arguments":{"id":"r"}}' "DELETED"
+_send_qemu_cmd $QEMU_HANDLE '{"execute":"block-export-del",
+ "arguments":{"id":"w"}}' "DELETED"
+_send_qemu_cmd $QEMU_HANDLE '{"execute":"nbd-server-stop"}' "return"
+
+echo
+echo "=== Limit nbd server max-connections ==="
+echo
+# When max-connections is 1, no images advertise multi-conn, even when
+# explicitly requested per export
+_send_qemu_cmd $QEMU_HANDLE '{"execute":"nbd-server-start",
+ "arguments":{"max-connections":1, "addr":{"type":"unix",
+ "data":{"path":"'"$nbd_unix_socket"'"}}}}' "return"
+_send_qemu_cmd $QEMU_HANDLE '{"execute":"block-export-add",
+ "arguments":{"type":"nbd", "id":"r", "node-name":"n",
+ "name":"r", "multi-conn":"on"}}' "return"
+nbdsh -u "nbd+unix:///r?socket=$nbd_unix_socket" -c '
+assert not h.can_multi_conn()
+h.shutdown()
+print("nbdsh passed")'
+_send_qemu_cmd $QEMU_HANDLE '{"execute":"block-export-del",
+ "arguments":{"id":"r"}}' "DELETED"
+_send_qemu_cmd $QEMU_HANDLE '{"execute":"block-export-add",
+ "arguments":{"type":"nbd", "id":"w", "node-name":"n",
+ "name":"w", "multi-conn":"on", "writable":true}}' "return"
+nbdsh -u "nbd+unix:///w?socket=$nbd_unix_socket" -c '
+assert not h.can_multi_conn()
+h.shutdown()
+print("nbdsh passed")'
+_send_qemu_cmd $QEMU_HANDLE '{"execute":"block-export-del",
+ "arguments":{"id":"w"}}' "DELETED"
+_send_qemu_cmd $QEMU_HANDLE '{"execute":"nbd-server-stop"}' "return"
+
+echo
+echo "=== Demonstrate parallel writers ==="
+echo
+_send_qemu_cmd $QEMU_HANDLE '{"execute":"nbd-server-start",
+ "arguments":{"addr":{"type":"unix",
+ "data":{"path":"'"$nbd_unix_socket"'"}}}}' "return"
+_send_qemu_cmd $QEMU_HANDLE '{"execute":"block-export-add",
+ "arguments":{"type":"nbd", "id":"w", "node-name":"n",
+ "name":"", "multi-conn":"on", "writable":true}}' "return"
+
+nbdsh -c '
+import os
+sock = os.getenv("nbd_unix_socket")
+h = []
+
+for i in range(3):
+ h.append(nbd.NBD())
+ h[i].connect_unix(sock)
+ assert h[i].can_multi_conn()
This is somewhat C in python, maybe:
handles = [nbd.NBD() for _ in range(3)]
for h in handles:
h.connect_unix(sock)
assert h.can_multi_con()
Since assert will abort the test, and we don't handle
exceptions, failure will not shutdown the connections
but it should not matter for the purpose of a test.
+
+buf1 = h[0].pread(1024 * 1024, 0)
+if buf1 != b"\x01" * 1024 * 1024:
+ print("Unexpected initial read")
Not clear when we initialize the buffer to \x01 - is this the qemu-io above?
+buf2 = b"\x03" * 1024 * 1024
+h[1].pwrite(buf2, 0)
+h[2].flush()
+buf1 = h[0].pread(1024 * 1024, 0)
+if buf1 == buf2:
+ print("Flush appears to be consistent across connections")
buf1 was the initial content, buf2 is the new content, but now we override
but1 to check that the right was flushed. It will be be better to use different
names like inittial_data, updated_data, current_data.
This block is the most important part of the test, showing that we can write
in one connection, flush in the second, and read the written block in the third.
Maybe add a comment about this? I think it will help someone else trying
to understand what this part is trying to test.
+
+for i in range(3):
+ h[i].shutdown()
for h in handles:
h.shutdown()
+'
+
+_send_qemu_cmd $QEMU_HANDLE '{"execute":"block-export-del",
+ "arguments":{"id":"w"}}' "DELETED"
+_send_qemu_cmd $QEMU_HANDLE '{"execute":"nbd-server-stop"}' "return"
+_send_qemu_cmd $QEMU_HANDLE '{"execute":"quit"}' "return"
+wait=yes _cleanup_qemu
+
+# success, all done
+echo '*** done'
+rm -f $seq.full
+status=0
diff --git a/tests/qemu-iotests/tests/nbd-multiconn.out b/tests/qemu-iotests/tests/nbd-multiconn.out
new file mode 100644
index 000000000000..a06428e1536a
--- /dev/null
+++ b/tests/qemu-iotests/tests/nbd-multiconn.out
@@ -0,0 +1,112 @@
+QA output created by nbd-multiconn
+
+=== Initial image setup ===
+
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=4194304
+wrote 2097152/2097152 bytes at offset 0
+2 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+wrote 2097152/2097152 bytes at offset 2097152
+2 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+{"execute":"qmp_capabilities"}
+{"return": {}}
+{"execute":"blockdev-add",
+ "arguments":{"driver":"IMGFMT", "node-name":"n",
+ "file":{"driver":"file", "filename":"TEST_DIR/t.IMGFMT"}}}
+{"return": {}}
+
+=== Default nbd server settings ===
+
+{"execute":"nbd-server-start",
+ "arguments":{"addr":{"type":"unix",
+ "data":{"path":"SOCK_DIR/qemu-nbd.sock"}}}}
+{"return": {}}
+{"execute":"block-export-add",
+ "arguments":{"type":"nbd", "id":"r", "node-name":"n",
+ "name":"r"}}
+{"return": {}}
+{"execute":"block-export-add",
+ "arguments":{"type":"nbd", "id":"w", "node-name":"n",
+ "name":"w", "writable":true}}
+{"return": {}}
+nbdsh passed
+nbdsh passed
+{"execute":"block-export-del",
+ "arguments":{"id":"r"}}
+{"return": {}}
+{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, "event": "BLOCK_EXPORT_DELETED", "data": {"id": "r"}}
+{"execute":"block-export-del",
+ "arguments":{"id":"w"}}
+{"return": {}}
+{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, "event": "BLOCK_EXPORT_DELETED", "data": {"id": "w"}}
+
+=== Per-export overrides of defaults ===
+
+{"execute":"block-export-add",
+ "arguments":{"type":"nbd", "id":"r", "node-name":"n",
+ "name":"r", "multi-conn":"off"}}
+{"return": {}}
+{"execute":"block-export-add",
+ "arguments":{"type":"nbd", "id":"w", "node-name":"n",
+ "name":"w", "multi-conn":"on", "writable":true}}
+{"return": {}}
+nbdsh passed
+nbdsh passed
+{"execute":"block-export-del",
+ "arguments":{"id":"r"}}
+{"return": {}}
+{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, "event": "BLOCK_EXPORT_DELETED", "data": {"id": "r"}}
+{"execute":"block-export-del",
+ "arguments":{"id":"w"}}
+{"return": {}}
+{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, "event": "BLOCK_EXPORT_DELETED", "data": {"id": "w"}}
+{"execute":"nbd-server-stop"}
+{"return": {}}
+
+=== Limit nbd server max-connections ===
+
+{"execute":"nbd-server-start",
+ "arguments":{"max-connections":1, "addr":{"type":"unix",
+ "data":{"path":"SOCK_DIR/qemu-nbd.sock"}}}}
+{"return": {}}
+{"execute":"block-export-add",
+ "arguments":{"type":"nbd", "id":"r", "node-name":"n",
+ "name":"r", "multi-conn":"on"}}
+{"return": {}}
+nbdsh passed
+{"execute":"block-export-del",
+ "arguments":{"id":"r"}}
+{"return": {}}
+{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, "event": "BLOCK_EXPORT_DELETED", "data": {"id": "r"}}
+{"execute":"block-export-add",
+ "arguments":{"type":"nbd", "id":"w", "node-name":"n",
+ "name":"w", "multi-conn":"on", "writable":true}}
+{"return": {}}
+nbdsh passed
+{"execute":"block-export-del",
+ "arguments":{"id":"w"}}
+{"return": {}}
+{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, "event": "BLOCK_EXPORT_DELETED", "data": {"id": "w"}}
+{"execute":"nbd-server-stop"}
+{"return": {}}
+
+=== Demonstrate parallel writers ===
+
+{"execute":"nbd-server-start",
+ "arguments":{"addr":{"type":"unix",
+ "data":{"path":"SOCK_DIR/qemu-nbd.sock"}}}}
+{"return": {}}
+{"execute":"block-export-add",
+ "arguments":{"type":"nbd", "id":"w", "node-name":"n",
+ "name":"", "multi-conn":"on", "writable":true}}
+{"return": {}}
+Flush appears to be consistent across connections
+{"execute":"block-export-del",
+ "arguments":{"id":"w"}}
+{"return": {}}
+{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, "event": "BLOCK_EXPORT_DELETED", "data": {"id": "w"}}
+{"execute":"nbd-server-stop"}
+{"return": {}}
+{"execute":"quit"}
+{"return": {}}
+{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, "event": "SHUTDOWN", "data": {"guest": false, "reason": "host-qmp-quit"}}
Nothing about the contents here says anything about the actual test
except the "Flush appears..." line.
+*** done
--
2.35.1
Looks good, feel free to ignore the style comments and suggestion to rewrite
the test in python.
Nir