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qmp: Document COMMAND_DROPPED design flaw

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Events are broadcast to all monitors.  If another monitor's client has
a command with the same ID in flight, the event will incorrectly claim
that command was dropped.  This must be fixed before out-of-band
execution can graduate from "experimental".

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20180703085358.13941-5-armbru@redhat.com>
This commit is contained in:
Markus Armbruster 2018-07-03 10:53:30 +02:00
parent 71696cc66c
commit d621cfe0a1
2 changed files with 9 additions and 0 deletions
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6
monitor.c
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@ -4331,6 +4331,12 @@ static void handle_qmp_command(JSONMessageParser *parser, GQueue *tokens)
/* 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);
/*
* FIXME @id's scope is just @mon, and broadcasting it is
* wrong. If another monitor's client has a command with
* the same ID in flight, the event will incorrectly claim
* that command was dropped.
*/
qapi_event_send_command_dropped(id,
COMMAND_DROP_REASON_QUEUE_FULL,
&error_abort);

3
qapi/misc.json
View File

@ -3454,6 +3454,9 @@
# only be dropped when the oob capability is enabled.
#
# @id: The dropped command's "id" field.
# FIXME Broken by design. Events are broadcast to all monitors. If
# another monitor's client has a command with the same ID in flight,
# the event will incorrectly claim that command was dropped.
#
# @reason: The reason why the command is dropped.
#