diff options
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/devel/qapi-code-gen.txt | 63 | ||||
| -rw-r--r-- | docs/interop/qmp-intro.txt | 13 | ||||
| -rw-r--r-- | docs/interop/qmp-spec.txt | 85 |
3 files changed, 86 insertions, 75 deletions
diff --git a/docs/devel/qapi-code-gen.txt b/docs/devel/qapi-code-gen.txt index d3b0990983..c2e11465f0 100644 --- a/docs/devel/qapi-code-gen.txt +++ b/docs/devel/qapi-code-gen.txt @@ -624,62 +624,48 @@ its return value. In rare cases, QAPI cannot express a type-safe representation of a corresponding Client JSON Protocol command. You then have to suppress generation of a marshalling function by including a key 'gen' with -boolean value false, and instead write your own function. Please try -to avoid adding new commands that rely on this, and instead use -type-safe unions. For an example of this usage: +boolean value false, and instead write your own function. For +example: { 'command': 'netdev_add', 'data': {'type': 'str', 'id': 'str'}, 'gen': false } +Please try to avoid adding new commands that rely on this, and instead +use type-safe unions. + Normally, the QAPI schema is used to describe synchronous exchanges, where a response is expected. But in some cases, the action of a command is expected to change state in a way that a successful response is not possible (although the command will still return a normal dictionary error on failure). When a successful reply is not -possible, the command expression should include the optional key +possible, the command expression includes the optional key 'success-response' with boolean value false. So far, only QGA makes use of this member. -A command can be declared to support Out-Of-Band (OOB) execution. By -default, commands do not support OOB. To declare a command that -supports it, the schema includes an extra 'allow-oob' field. For -example: +Key 'allow-oob' declares whether the command supports out-of-band +(OOB) execution. It defaults to false. For example: { 'command': 'migrate_recover', 'data': { 'uri': 'str' }, 'allow-oob': true } -To execute a command with out-of-band priority, the client specifies -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 support out-of-band execution will -still be run in-band. +See qmp-spec.txt for out-of-band execution syntax and semantics. -Under normal QMP command execution, the following apply to each -command: +Commands supporting out-of-band execution can still be executed +in-band. -- They are executed in order, -- They run only in main thread of QEMU, -- They run with the BQL held. +When a command is executed in-band, its handler runs in the main +thread with the BQL held. -When a command is executed with OOB, the following changes occur: +When a command is executed out-of-band, its handler runs in a +dedicated monitor I/O thread with the BQL *not* held. -- They can be completed before a pending in-band command, -- They run in a dedicated monitor thread, -- They run with the BQL not held. +An OOB-capable command handler must satisfy the following conditions: -OOB command handlers must satisfy the following conditions: - -- It terminates quickly, -- It does not invoke system calls that may block, +- It terminates quickly. +- It does not invoke system calls that may block. - It does not access guest RAM that may block when userfaultfd is - enabled for postcopy live migration, + enabled for postcopy live migration. - It takes only "fast" locks, i.e. all critical sections protected by any lock it takes also satisfy the conditions for OOB command handler code. @@ -688,17 +674,18 @@ The restrictions on locking limit access to shared state. Such access requires synchronization, but OOB commands can't take the BQL or any other "slow" lock. -If in doubt, do not implement OOB execution support. +When in doubt, do not implement OOB execution support. -A command may use the optional 'allow-preconfig' key to permit its execution -at early runtime configuration stage (preconfig runstate). -If not specified then a command defaults to 'allow-preconfig': false. +Key 'allow-preconfig' declares whether the command is available before +the machine is built. It defaults to false. For example: -An example of declaring a command that is enabled during preconfig: { 'command': 'qmp_capabilities', 'data': { '*enable': [ 'QMPCapability' ] }, 'allow-preconfig': true } +QMP is available before the machine is built only when QEMU was +started with --preconfig. + === Events === Usage: { 'event': STRING, '*data': COMPLEX-TYPE-NAME-OR-DICT, diff --git a/docs/interop/qmp-intro.txt b/docs/interop/qmp-intro.txt index 900d69d612..9d54a718b8 100644 --- a/docs/interop/qmp-intro.txt +++ b/docs/interop/qmp-intro.txt @@ -52,13 +52,14 @@ Escape character is '^]'. "QMP": { "version": { "qemu": { - "micro": 50, - "minor": 6, - "major": 1 - }, - "package": "" - }, + "micro": 0, + "minor": 0, + "major": 3 + }, + "package": "v3.0.0" + }, "capabilities": [ + "oob" ] } } diff --git a/docs/interop/qmp-spec.txt b/docs/interop/qmp-spec.txt index 6fa193a80b..1566b8ae5e 100644 --- a/docs/interop/qmp-spec.txt +++ b/docs/interop/qmp-spec.txt @@ -77,52 +77,65 @@ The greeting message format is: is the same of the query-version command) - The "capabilities" member specify the availability of features beyond the baseline specification; the order of elements in this array has no - particular significance, so a client must search the entire array - when looking for a particular capability + particular significance. 2.2.1 Capabilities ------------------ Currently supported capabilities are: -- "oob": the QMP server supports "Out-Of-Band" (OOB) command - execution. For more details, please see the "run-oob" parameter in - the "Issuing Commands" section below. Not all commands allow this - "oob" execution. The "query-qmp-schema" command can be used to - inspect which commands support "oob" execution. - -QMP clients can get a list of supported QMP capabilities of the QMP -server in the greeting message mentioned above. By default, all the -capabilities are off. To enable any QMP capabilities, the QMP client -needs to send the "qmp_capabilities" command with an extra parameter -for the requested capabilities. +- "oob": the QMP server supports "out-of-band" (OOB) command + execution, as described in section "2.3.1 Out-of-band execution". 2.3 Issuing Commands -------------------- The format for command execution is: -{ "execute": json-string, "arguments": json-object, "id": json-value, - "control": json-object } +{ "execute": json-string, "arguments": json-object, "id": json-value } + +or + +{ "exec-oob": json-string, "arguments": json-object, "id": json-value } Where, -- The "execute" member identifies the command to be executed by the Server +- The "execute" or "exec-oob" member identifies the command to be + executed by the server. The latter requests out-of-band execution. - The "arguments" member is used to pass any arguments required for the execution of the command, it is optional when no arguments are required. Each command documents what contents will be considered valid when handling the json-argument - The "id" member is a transaction identification associated with the - command execution. It is required for all commands if the OOB - - capability was enabled at startup, and optional otherwise. The same - "id" field will be part of the response if 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 optional, and currently only used for - out-of-band execution. The handling or response of an "oob" command - can overtake prior in-band commands. To enable "oob" handling of a - particular command, just provide a control field with: { "control": - { "run-oob": true } } + command execution, it is optional and will be part of the response + if provided. The "id" member can be any json-value. A json-number + incremented for each successive command works fine. + +2.3.1 Out-of-band execution +--------------------------- + +The server normally reads, executes and responds to one command after +the other. The client therefore receives command responses in issue +order. + +With out-of-band execution enabled via capability negotiation (section +4.), the server reads and queues commands as they arrive. It executes +commands from the queue one after the other. Commands executed +out-of-band jump the queue: the command get executed right away, +possibly overtaking prior in-band commands. The client may therefore +receive such a command's response before responses from prior in-band +commands. + +To be able to match responses back to their commands, the client needs +to pass "id" with out-of-band commands. Passing it with all commands +is recommended for clients that accept capability "oob". + +If the client sends in-band commands faster than the server can +execute them, the server will eventually drop commands to limit the +queue length. The sever sends event COMMAND_DROPPED then. + +Only a few commands support out-of-band execution. The ones that do +have "allow-oob": true in output of query-qmp-schema. 2.4 Commands Responses ---------------------- @@ -223,12 +236,13 @@ This section provides some examples of real QMP usage, in all of them 3.1 Server greeting ------------------- -S: { "QMP": { "version": { "qemu": { "micro": 50, "minor": 6, "major": 1 }, - "package": ""}, "capabilities": []}} +S: { "QMP": {"version": {"qemu": {"micro": 0, "minor": 0, "major": 3}, + "package": "v3.0.0"}, "capabilities": ["oob"] } } + +3.2 Capabilities negotiation +---------------------------- -3.2 Client QMP negotiation --------------------------- -C: { "execute": "qmp_capabilities" } +C: { "execute": "qmp_capabilities", "arguments": { "enable": ["oob"] } } S: { "return": {}} 3.3 Simple 'stop' execution @@ -255,6 +269,15 @@ S: { "error": { "class": "GenericError", "desc": "Invalid JSON syntax" } } S: { "timestamp": { "seconds": 1258551470, "microseconds": 802384 }, "event": "POWERDOWN" } +3.7 Out-of-band execution +------------------------- + +C: { "exec-oob": "migrate-pause", "id": 42 } +S: { "id": 42, + "error": { "class": "GenericError", + "desc": "migrate-pause is currently only supported during postcopy-active state" } } + + 4. Capabilities Negotiation =========================== |