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[libvirt] [PATCH 2/6] qemu: virsh wrapper for qemu events



Any new API deserves a good virsh wrapper :)

    qemu-monitor-event [<domain>] [<event>] [--pretty] [--loop] [--timeout <number>]

It helps that we already have an event loop running in a dedicated
thread, so a blocking read() on a pipe-to-self is sufficient to
handle all three means of ending the command: SIGINT, timeout, and
oneshot behavior of an event received.

For an example session (once subsequent qemu patches are applied):

$ virsh -c qemu:///system qemu-monitor-event --event SHUTDOWN &
$ virsh -c qemu:///system start f18-live
Domain f18-live started

$ virsh -c qemu:///system destroy f18-live
Domain f18-live destroyed

event SHUTDOWN at 1391212552.026544 for domain f18-live: (null)
events received: 1

[1]+  Done                    virsh -c qemu:///system qemu-monitor-event --event SHUTDOWN
$

* tools/virsh-domain.c (cmdQemuMonitorEvent): New command.
* tools/virsh.pod (qemu-monitor-event): Document it.

Signed-off-by: Eric Blake <eblake redhat com>
---
 tools/virsh-domain.c | 193 +++++++++++++++++++++++++++++++++++++++++++++++++++
 tools/virsh.pod      |  27 +++++--
 2 files changed, 216 insertions(+), 4 deletions(-)

diff --git a/tools/virsh-domain.c b/tools/virsh-domain.c
index ce7aea9..a6dc80a 100644
--- a/tools/virsh-domain.c
+++ b/tools/virsh-domain.c
@@ -7933,6 +7933,193 @@ cleanup:
 }

 /*
+ * "qemu-monitor-event" command
+ */
+static int vshEventFd = -1;
+
+static void
+vshEventInt(int sig ATTRIBUTE_UNUSED,
+            siginfo_t *siginfo ATTRIBUTE_UNUSED,
+            void *context ATTRIBUTE_UNUSED)
+{
+    if (vshEventFd >= 0)
+        ignore_value(safewrite(vshEventFd, "i", 1));
+}
+
+static void
+vshEventTimeout(int timer ATTRIBUTE_UNUSED,
+                void *opaque ATTRIBUTE_UNUSED)
+{
+    if (vshEventFd >= 0)
+        ignore_value(safewrite(vshEventFd, "t", 1));
+}
+
+struct vshEventData {
+    vshControl *ctl;
+    bool loop;
+    bool pretty;
+    int count;
+};
+typedef struct vshEventData vshEventData;
+
+static void
+vshEventPrint(virConnectPtr conn ATTRIBUTE_UNUSED, virDomainPtr dom,
+              const char *event, long long seconds, unsigned int micros,
+              const char *details, void *opaque)
+{
+    vshEventData *data = opaque;
+    virJSONValuePtr pretty = NULL;
+    char *str = NULL;
+
+    if (data->pretty && details) {
+        pretty = virJSONValueFromString(details);
+        if (pretty && (str = virJSONValueToString(pretty, true)))
+            details = str;
+    }
+    vshPrint(data->ctl, "event %s at %lld.%06u for domain %s: %s\n",
+             event, seconds, micros, virDomainGetName(dom), NULLSTR(details));
+    data->count++;
+    if (!data->loop && vshEventFd >= 0)
+        ignore_value(safewrite(vshEventFd, "done", 1));
+
+    VIR_FREE(str);
+}
+
+static const vshCmdInfo info_qemu_monitor_event[] = {
+    {.name = "help",
+     .data = N_("QEMU Monitor Events")
+    },
+    {.name = "desc",
+     .data = N_("Listen for QEMU Monitor Events")
+    },
+    {.name = NULL}
+};
+
+static const vshCmdOptDef opts_qemu_monitor_event[] = {
+    {.name = "domain",
+     .type = VSH_OT_DATA,
+     .help = N_("filter by domain name, id or uuid")
+    },
+    {.name = "event",
+     .type = VSH_OT_DATA,
+     .help = N_("filter by event name")
+    },
+    {.name = "pretty",
+     .type = VSH_OT_BOOL,
+     .help = N_("pretty-print any JSON output")
+    },
+    {.name = "loop",
+     .type = VSH_OT_BOOL,
+     .help = N_("loop until timeout or interrupt, rather than one-shot")
+    },
+    {.name = "timeout",
+     .type = VSH_OT_INT,
+     .help = N_("timeout seconds")
+    },
+    {.name = NULL}
+};
+
+static bool
+cmdQemuMonitorEvent(vshControl *ctl, const vshCmd *cmd)
+{
+    virDomainPtr dom = NULL;
+    bool ret = false;
+    unsigned int flags = 0;
+    int timerId = -1;
+    int eventId = -1;
+    int fd[2] = { -1, -1 };
+    int timeout = 0;
+    const char *event = NULL;
+    struct sigaction sig_action;
+    struct sigaction old_sig_action;
+    int rv;
+    char buf = '\0';
+    vshEventData data;
+
+    data.ctl = ctl;
+    data.loop = vshCommandOptBool(cmd, "loop");
+    data.pretty = vshCommandOptBool(cmd, "pretty");
+    data.count = 0;
+    if ((rv = vshCommandOptInt(cmd, "timeout", &timeout)) < 0 ||
+        (rv > 0 && timeout < 1)) {
+        vshError(ctl, "%s", _("invalid timeout"));
+        return false;
+    } else if (rv > 0) {
+        /* Ensure that we can multiply by 1000 without overflowing. */
+        if (timeout > INT_MAX / 1000) {
+            vshError(ctl, "%s", _("timeout is too big"));
+            return false;
+        }
+        timeout *= 1000;
+    }
+    if (vshCommandOptString(cmd, "event", &event) < 0)
+        return false;
+
+    if (vshCommandOptBool(cmd, "domain"))
+        dom = vshCommandOptDomain(ctl, cmd, NULL);
+
+    /* virsh.c already set up an event loop; this command blocks until
+     * a callback informs us that we are done.  */
+    if (pipe2(fd, O_CLOEXEC) < 0)
+        goto cleanup;
+    vshEventFd = fd[1];
+
+    if ((eventId = virConnectDomainQemuMonitorEventRegister(ctl->conn, dom,
+                                                            event,
+                                                            vshEventPrint,
+                                                            &data, NULL,
+                                                            flags)) < 0)
+        goto cleanup;
+
+    sig_action.sa_sigaction = vshEventInt;
+    sig_action.sa_flags = SA_SIGINFO;
+    sigemptyset(&sig_action.sa_mask);
+    sigaction(SIGINT, &sig_action, &old_sig_action);
+
+    if (timeout)
+        timerId = virEventAddTimeout(timeout, vshEventTimeout, NULL, NULL);
+
+    while ((rv = read(fd[0], &buf, 1)) < 0 && errno == EINTR);
+    if (rv != 1) {
+        char ebuf[1024];
+
+        if (!rv)
+            errno = EPIPE;
+        vshError(ctl, _("failed to determine loop exit status: %s"),
+                 virStrerror(errno, ebuf, sizeof(ebuf)));
+        goto cleanup;
+    }
+
+    switch (buf) {
+    case 'i':
+        vshPrint(ctl, _("event loop interrupted\n"));
+        break;
+    case 't':
+        vshPrint(ctl, _("event loop timed out\n"));
+        break;
+    }
+    vshPrint(ctl, _("events received: %d\n"), data.count);
+    if (data.count)
+        ret = true;
+
+cleanup:
+    if (eventId >= 0) {
+        sigaction(SIGINT, &old_sig_action, NULL);
+        if (virConnectDomainQemuMonitorEventDeregister(ctl->conn, eventId) < 0)
+            ret = false;
+    }
+    vshEventFd = -1;
+    VIR_FORCE_CLOSE(fd[0]);
+    VIR_FORCE_CLOSE(fd[1]);
+    if (timerId >= 0)
+        virEventRemoveTimeout(timerId);
+    if (dom)
+        virDomainFree(dom);
+
+    return ret;
+}
+
+/*
  * "qemu-attach" command
  */
 static const vshCmdInfo info_qemu_attach[] = {
@@ -10903,6 +11090,12 @@ const vshCmdDef domManagementCmds[] = {
      .info = info_qemu_monitor_command,
      .flags = 0
     },
+    {.name = "qemu-monitor-event",
+     .handler = cmdQemuMonitorEvent,
+     .opts = opts_qemu_monitor_event,
+     .info = info_qemu_monitor_event,
+     .flags = 0
+    },
     {.name = "qemu-agent-command",
      .handler = cmdQemuAgentCommand,
      .opts = opts_qemu_agent_command,
diff --git a/tools/virsh.pod b/tools/virsh.pod
index d052b3a..22b1373 100644
--- a/tools/virsh.pod
+++ b/tools/virsh.pod
@@ -3272,12 +3272,15 @@ variables, and defaults to C<vi>.

 =back

-=head1 QEMU-SPECIFIC COMMANDS
+=head1 HYPERVISOR-SPECIFIC COMMANDS

 NOTE: Use of the following commands is B<strongly> discouraged.  They
 can cause libvirt to become confused and do the wrong thing on subsequent
-operations.  Once you have used this command, please do not report
-problems to the libvirt developers; the reports will be ignored.
+operations.  Once you have used these commands, please do not report
+problems to the libvirt developers; the reports will be ignored.  If
+you find that these commands are the only way to accomplish something,
+then it is better to request that the feature be added as a first-class
+citizen in the regular libvirt library.

 =over 4

@@ -3316,7 +3319,8 @@ and the monitor uses QMP, then the output will be pretty-printed.  If more
 than one argument is provided for I<command>, they are concatenated with a
 space in between before passing the single command to the monitor.

-=item B<qemu-agent-command> I<domain> [I<--timeout> I<seconds> | I<--async> | I<--block>] I<command>...
+=item B<qemu-agent-command> I<domain> [I<--timeout> I<seconds> | I<--async> |
+I<--block>] I<command>...

 Send an arbitrary guest agent command I<command> to domain I<domain> through
 qemu agent.
@@ -3326,6 +3330,21 @@ When I<--aysnc> is given, the command waits for timeout whether success or
 failed. And when I<--block> is given, the command waits forever with blocking
 timeout.

+=item B<qemu-monitor-event> [I<domain>] [I<--event> I<event-name>] [I<--loop>]
+[I<--timeout> I<seconds>] [I<--pretty>]
+
+Wait for arbitrary QEMU monitor events to occur, and print out the
+details of events as they happen.  The events can optionally be filtered
+by I<domain> or I<event-name>.  The 'query-events' QMP command can be
+used via I<qemu-monitor-command> to learn what events are supported.
+
+By default, this command is one-shot, and returns success once an event
+occurs; you can send SIGINT (usually via C<Ctrl-C>) to quit immediately.
+If I<--timeout> is specified, the command gives up waiting for events
+after I<seconds> have elapsed.  With I<--loop>, the command prints all
+events until a timeout or interrupt key.  If I<--pretty> is specified,
+any JSON event details are pretty-printed for better legibility.
+
 =item B<lxc-enter-namespace> I<domain> -- /path/to/binary [arg1, [arg2, ...]]

 Enter the namespace of I<domain> and execute the command C</path/to/binary>
-- 
1.8.5.3


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