From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:36391) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dxmAv-0007BQ-Eq for qemu-devel@nongnu.org; Thu, 28 Sep 2017 23:41:19 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dxmAu-0007t4-3p for qemu-devel@nongnu.org; Thu, 28 Sep 2017 23:41:17 -0400 Received: from mx1.redhat.com ([209.132.183.28]:59196) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dxmAt-0007rZ-RX for qemu-devel@nongnu.org; Thu, 28 Sep 2017 23:41:16 -0400 From: Peter Xu Date: Fri, 29 Sep 2017 11:38:44 +0800 Message-Id: <20170929033844.26935-23-peterx@redhat.com> In-Reply-To: <20170929033844.26935-1-peterx@redhat.com> References: <20170929033844.26935-1-peterx@redhat.com> Subject: [Qemu-devel] [RFC v2 22/22] docs: update QMP documents for OOB commands List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Paolo Bonzini , "Daniel P . Berrange" , Stefan Hajnoczi , Fam Zheng , Juan Quintela , mdroth@linux.vnet.ibm.com, peterx@redhat.com, Eric Blake , Laurent Vivier , =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= , Markus Armbruster , "Dr . David Alan Gilbert" List-ID: Update both the developer and spec for the new QMP OOB (Out-Of-Band) command. Signed-off-by: Peter Xu --- docs/devel/qapi-code-gen.txt | 51 +++++++++++++++++++++++++++++++++++++++----- docs/interop/qmp-spec.txt | 24 ++++++++++++++++++--- 2 files changed, 67 insertions(+), 8 deletions(-) diff --git a/docs/devel/qapi-code-gen.txt b/docs/devel/qapi-code-gen.txt index f04c63fe82..8597fdb087 100644 --- a/docs/devel/qapi-code-gen.txt +++ b/docs/devel/qapi-code-gen.txt @@ -556,7 +556,8 @@ following example objects: Usage: { 'command': STRING, '*data': COMPLEX-TYPE-NAME-OR-DICT, '*returns': TYPE-NAME, '*boxed': true, - '*gen': false, '*success-response': false } + '*gen': false, '*success-response': false, + '*allow-oob': false } Commands are defined by using a dictionary containing several members, where three members are most common. The 'command' member is a @@ -636,6 +637,44 @@ possible, the command expression should include the optional key 'success-response' with boolean value false. So far, only QGA makes use of this member. +Most of the QMP commands are handled sequentially in such a order: +Firstly, the JSON Parser parses the command request into some internal +message, delivers the message to QMP dispatchers. Secondly, the QMP +dispatchers will handle the commands one by one in time order, respond +when necessary. For some commands that always complete "quickly" can +instead be executed directly during parsing, at the QMP client's +request. This kind of commands that allow direct execution is called +"out-of-band" ("oob" as shortcut) commands. The response can overtake +prior in-band commands' responses. By default, commands are always +in-band. We need to explicitly specify "allow-oob" to "True" to show +that one command can be run out-of-band. + +One thing to mention for developers is that, although out-of-band +execution of commands benefit from quick and asynchronous execution, +it need to satisfy at least the following: + +(1) It is extremely quick and never blocks, so that its execution will + not block parsing routine of any other monitors. + +(2) It does not need BQL, since the parser can be run without BQL, + while the dispatcher is always with BQL held. + +If not, the command is not suitable to be allowed to run out-of-band, +and it should set its "allow-oob" to "False". Whether a command is +allowed to run out-of-band can also be introspected using +query-qmp-schema command. Please see the section "Client JSON +Protocol introspection" for more information. + +To execute a command in out-of-band way, we need to specify the +"control" field in the request, with "run-oob" set to true. Example: + + => { "execute": "command-support-oob", + "arguments": { ... }, + "control": { "run-oob": true } } + <= { "return": { } } + +Without it, even the commands that supports out-of-band execution will +still be run in-band. === Events === @@ -739,10 +778,12 @@ references by name. QAPI schema definitions not reachable that way are omitted. The SchemaInfo for a command has meta-type "command", and variant -members "arg-type" and "ret-type". On the wire, the "arguments" -member of a client's "execute" command must conform to the object type -named by "arg-type". The "return" member that the server passes in a -success response conforms to the type named by "ret-type". +members "arg-type", "ret-type" and "allow-oob". On the wire, the +"arguments" member of a client's "execute" command must conform to the +object type named by "arg-type". The "return" member that the server +passes in a success response conforms to the type named by +"ret-type". When "allow-oob" is set, it means the command supports +out-of-band execution. If the command takes no arguments, "arg-type" names an object type without members. Likewise, if the command returns nothing, "ret-type" diff --git a/docs/interop/qmp-spec.txt b/docs/interop/qmp-spec.txt index f8b5356015..c345f235a7 100644 --- a/docs/interop/qmp-spec.txt +++ b/docs/interop/qmp-spec.txt @@ -83,16 +83,21 @@ The greeting message format is: 2.2.1 Capabilities ------------------ -As of the date this document was last revised, no server or client -capability strings have been defined. +Currently supported capabilities: +- "oob": it means the QMP server supports "Out-Of-Band" command + execution. For more detail, please see "run-oob" parameter in + "Issuing Commands" section below. Not all commands allow this "oob" + execution. One can know whether one command supports "oob" by + "query-qmp-schema" command. 2.3 Issuing Commands -------------------- The format for command execution is: -{ "execute": json-string, "arguments": json-object, "id": json-value } +{ "execute": json-string, "arguments": json-object, "id": json-value, + "control": json-dict } Where, @@ -106,6 +111,14 @@ The format for command execution is: provided. The "id" member can be any json-value, although most clients merely use a json-number incremented for each successive command +- The "control" member is optionally, and currently only used for + "out-of-band" execution. For some commands that always complete + "quickly" can be executed directly during parsing at the QMP + client's request. This kind of commands that allow direct execution + is called "out-of-band" ("oob" as shortcut) commands. The response + of "oob" commands can overtake prior in-band commands' responses. + To enable "oob" feature, just provide a control field with: + { "control": { "run-oob": true } } 2.4 Commands Responses ---------------------- @@ -113,6 +126,11 @@ The format for command execution is: There are two possible responses which the Server will issue as the result of a command execution: success or error. +As long as the commands were issued with a proper "id" field, then the +same "id" field will be attached in the corresponding response message +so that requests and responses can match. Clients should drop all the +responses that are with unknown "id" field. + 2.4.1 success ------------- -- 2.13.5