qmp: introduce QMPCapability

There were no QMP capabilities defined.  Define the first capability,
"oob", to allow out-of-band messages.

After this patch, we will allow QMP clients to enable QMP capabilities
when sending the first "qmp_capabilities" command.  Originally we are
starting QMP session with no arguments like:

  { "execute": "qmp_capabilities" }

Now we can enable some QMP capabilities using (take OOB as example,
which is the only capability that we support):

  { "execute": "qmp_capabilities",
    "arguments": { "enable": [ "oob" ] } }

When the "arguments" key is not provided, no capability is enabled.

For capability "oob", the monitor needs to be run on a dedicated IO
thread, otherwise the command will fail.  For example, trying to enable
OOB on a MUXed typed QMP monitor will fail.

One thing to mention is that QMP capabilities are per-monitor, and also
when the connection is closed due to some reason, the capabilities will
be reset.

Also, touch up qmp-test.c to test the new bits.

Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20180309090006.10018-11-peterx@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
[eblake: touch up commit message]
Signed-off-by: Eric Blake <eblake@redhat.com>
This commit is contained in:
Peter Xu 2018-03-09 16:59:53 +08:00 committed by Eric Blake
parent a5ed352596
commit 02130314d8
3 changed files with 110 additions and 9 deletions

View file

@ -10,21 +10,47 @@
#
# Enable QMP capabilities.
#
# Arguments: None.
# Arguments:
#
# @enable: An optional list of QMPCapability values to enable. The
# client must not enable any capability that is not
# mentioned in the QMP greeting message. If the field is not
# provided, it means no QMP capabilities will be enabled.
# (since 2.12)
#
# Example:
#
# -> { "execute": "qmp_capabilities" }
# -> { "execute": "qmp_capabilities",
# "arguments": { "enable": [ "oob" ] } }
# <- { "return": {} }
#
# Notes: This command is valid exactly when first connecting: it must be
# issued before any other command will be accepted, and will fail once the
# monitor is accepting other commands. (see qemu docs/interop/qmp-spec.txt)
#
# The QMP client needs to explicitly enable QMP capabilities, otherwise
# all the QMP capabilities will be turned off by default.
#
# Since: 0.13
#
##
{ 'command': 'qmp_capabilities' }
{ 'command': 'qmp_capabilities',
'data': { '*enable': [ 'QMPCapability' ] } }
##
# @QMPCapability:
#
# Enumeration of capabilities to be advertised during initial client
# connection, used for agreeing on particular QMP extension behaviors.
#
# @oob: QMP ability to support Out-Of-Band requests.
# (Please refer to qmp-spec.txt for more information on OOB)
#
# Since: 2.12
#
##
{ 'enum': 'QMPCapability',
'data': [ 'oob' ] }
##
# @VersionTriple: