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authorPeter Xu <peterx@redhat.com>2018-03-09 16:59:44 +0800
committerEric Blake <eblake@redhat.com>2018-03-19 14:58:36 -0500
commit378112b0020c4bc6c54e73e58046399f0e41b939 (patch)
tree7132a61466e3129f54bca128dc9cc85d44c039a7 /docs
parent99f2f54174a595e3ada6e4332fcd2b37ebb0d55d (diff)
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docs: update QMP documents for OOB commands
Update both the developer and spec for the new QMP OOB (Out-Of-Band) command. Signed-off-by: Peter Xu <peterx@redhat.com> Message-Id: <20180309090006.10018-2-peterx@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> [eblake: grammar tweaks] Signed-off-by: Eric Blake <eblake@redhat.com>
Diffstat (limited to 'docs')
-rw-r--r--docs/devel/qapi-code-gen.txt58
-rw-r--r--docs/interop/qmp-spec.txt36
2 files changed, 82 insertions, 12 deletions
diff --git a/docs/devel/qapi-code-gen.txt b/docs/devel/qapi-code-gen.txt
index 99d8123..a569d24 100644
--- a/docs/devel/qapi-code-gen.txt
+++ b/docs/devel/qapi-code-gen.txt
@@ -554,9 +554,12 @@ following example objects:
=== Commands ===
+--- General Command Layout ---
+
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': true }
Commands are defined by using a dictionary containing several members,
where three members are most common. The 'command' member is a
@@ -636,6 +639,49 @@ possible, the command expression should include 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:
+
+ { '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.
+
+Under normal QMP command execution, the following apply to each
+command:
+
+- They are executed in order,
+- They run only in main thread of QEMU,
+- They have the BQL taken during execution.
+
+When a command is executed with OOB, the following changes occur:
+
+- They can be completed before a pending in-band command,
+- They run in a dedicated monitor thread,
+- They do not take the BQL during execution.
+
+OOB command handlers must satisfy the following conditions:
+
+- It executes extremely fast,
+- It does not take any lock, or, it can take very small locks if all
+ critical regions also follow the rules for OOB command handler code,
+- 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.
+
+If in doubt, do not implement OOB execution support.
=== Events ===
@@ -739,10 +785,12 @@ 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 f8b5356..6fa193a 100644
--- a/docs/interop/qmp-spec.txt
+++ b/docs/interop/qmp-spec.txt
@@ -83,16 +83,27 @@ 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 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.
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-object }
Where,
@@ -102,10 +113,16 @@ The format for command execution is:
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 optional and 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
+ 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 } }
2.4 Commands Responses
----------------------
@@ -113,6 +130,11 @@ 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 have an unknown "id" field.
+
2.4.1 success
-------------