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monitor: send event when command queue full 

Set maximum QMP command queue length to 8.  If the queue is full,
instead of queuing the command, we directly return a "command-dropped"
event, telling the client that a specific command is dropped.

Note that this flow control mechanism is only valid if OOB is enabled.
If it's not, the effective queue length will always be 1, which strictly
follows original behavior of QMP command handling (which never drops
messages).

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20180309090006.10018-17-peterx@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
[eblake: commit message grammar, abort on failure to send event]
Signed-off-by: Eric Blake <eblake@redhat.com>
This commit is contained in:
Peter Xu 2018-03-09 16:59:59 +08:00 committed by Eric Blake
parent 8167d8bd36
commit bf1e730174
1 changed files with 17 additions and 1 deletions
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18
monitor.c
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@ -4010,6 +4010,8 @@ static void monitor_qmp_bh_dispatcher(void *data)
}
}
#define QMP_REQ_QUEUE_LEN_MAX (8)
static void handle_qmp_command(JSONMessageParser *parser, GQueue *tokens)
{
QObject *req, *id = NULL;
@ -4043,6 +4045,9 @@ static void handle_qmp_command(JSONMessageParser *parser, GQueue *tokens)
req_obj->req = req;
req_obj->need_resume = false;
/* Protect qmp_requests and fetching its length. */
qemu_mutex_lock(&mon->qmp.qmp_queue_lock);
/*
* If OOB is not enabled on the current monitor, we'll emulate the
* old behavior that we won't process the current monitor any more
@ -4052,6 +4057,18 @@ static void handle_qmp_command(JSONMessageParser *parser, GQueue *tokens)
if (!qmp_oob_enabled(mon)) {
monitor_suspend(mon);
req_obj->need_resume = true;
} else {
/* Drop the request if queue is full. */
if (mon->qmp.qmp_requests->length >= QMP_REQ_QUEUE_LEN_MAX) {
qemu_mutex_unlock(&mon->qmp.qmp_queue_lock);
qapi_event_send_command_dropped(id,
COMMAND_DROP_REASON_QUEUE_FULL,
&error_abort);
qobject_decref(id);
qobject_decref(req);
g_free(req_obj);
return;
}
}
/*
@ -4059,7 +4076,6 @@ static void handle_qmp_command(JSONMessageParser *parser, GQueue *tokens)
* handled in time order. Ownership for req_obj, req, id,
* etc. will be delivered to the handler side.
*/
qemu_mutex_lock(&mon->qmp.qmp_queue_lock);
g_queue_push_tail(mon->qmp.qmp_requests, req_obj);
qemu_mutex_unlock(&mon->qmp.qmp_queue_lock);