[libvirt] [Qemu-devel] [PATCH v4 4/5] qmp: full introspection support for QMP
Amos Kong
akong at redhat.com
Mon Jan 27 08:50:01 UTC 2014
On Mon, Jan 27, 2014 at 04:17:56PM +0800, Amos Kong wrote:
> CC Libvirt-list
>
> Original discussion:
> http://marc.info/?l=qemu-devel&m=139048842504757&w=2
> [Qemu-devel] [PATCH v4 0/5] QMP full introspection
>
> On Fri, Jan 24, 2014 at 06:48:31PM +0800, Fam Zheng wrote:
> > On Thu, 01/23 22:46, Amos Kong wrote:
> > > This patch introduces a new monitor command to query QMP schema
> > > information, the return data is a range of schema structs, which
> > > contains the useful metadata to help management to check supported
> > > features, QMP commands detail, etc.
> > >
> > > We use qapi-introspect.py to parse all json definition in
> > > qapi-schema.json, and generate a range of dictionaries with metadata.
> > > The query command will visit the dictionaries and fill the data
> > > to allocated struct tree. Then QMP infrastructure will convert
> > > the tree to json string and return to QMP client.
> > >
> > > TODO:
> > > Wenchao Xia is working to convert QMP events to qapi-schema.json,
> > > then event can also be queried by this interface.
> > >
> > > I will introduce another command 'query-qga-schema' to query QGA
> > > schema information, it's easy to add this support based on this
> > > patch.
> > >
> > > Signed-off-by: Amos Kong <akong at redhat.com>
> > > ---
> > > qapi-schema.json | 11 +++
> > > qmp-commands.hx | 42 +++++++++++
> > > qmp.c | 215 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
> > > 3 files changed, 268 insertions(+)
> > > +static DataObjectMemberList *qobject_to_list_memlist(QObject *data)
> > > +{
> > > + const QListEntry *lent;
> > > + DataObjectMemberList *list = NULL;
> > > + DataObjectMemberList **plist = &list;
> > > + QList *qlist = qobject_to_qlist(data);
> > > +
> > > + for (lent = qlist_first(qlist); lent; lent = qlist_next(lent)) {
> > > + DataObjectMemberList *entry = g_malloc0(sizeof(DataObjectMemberList));
> > > + entry->value = qobject_to_dataobjmem(lent->value);
> > > + entry->value->has_optional = true;
> > > + entry->value->has_name = true;
> > > + *plist = entry;
> > > + plist = &entry->next;
> > > + }
> > > +
> > > + return list;
> > > +}
> > > +
> > > +static DataObjectMemberList *qobject_to_memlist(QObject *data)
> >
> > This whole converting is cumbersome. You already did all the traversing through
> > the type jungle in python when generating this, it's not necessary to do the
> > similar thing again here.
>
> We can parse raw schemas and generate json string table, we can't
> directly return the string / qobject to monitor, C code has to convert
> the json to qobject, we have to revisit the qobject and convert them
> to DataObject/DataObjectMember/DataObject... structs.
>
> > Alternatively, I think we have a good reason to extend QMP framework as
> > necessary here, as we are doing "QMP introspection", which is a part of the
> > framework:
> >
> > * Define final output into qmp_schema_table[], no need to box it like:
> >
> > "{'_obj_member': 'False', '_obj_type': 'enum', '_obj_name':
> > 'ErrorClass', '_obj_data': {'data': ...
> >
> > just put it content of "qmp-introspection.output.txt" as a long string in
> > the header,
>
>
>
> > like you would generate in qobject_to_memlist:
> >
> > const char *qmp_schema_table =
> > "{ 'name': 'ErrorClass', 'type': 'enumeration', 'data': [...]},"
> > "{ 'name': '...', ...},"
>
> The keys are used for metadata might be 'recursive', 'optional', etc.
> It might exists problem in namespace, let's use '_obj_' or '_' prefix
> for the metadata keys.
>
> I used a nested dictionary to describe a DataObject, because we can
> store the metadata and definition to different level, it's helpful
> in parse the output by Libvirt.
>
> example:
> "{ 'type': 'NameInfo', 'data': {'*name': 'str', '*job': 'str'} }"
>
> It's good to store _type, _name, data to same level, but the metadata
> of items of data's value dictionary can't be appended to same level.
>
> "{ '_name': 'NameInfo', '_type': 'type',
> 'data': {
> 'name': 'str', '_name_optional': 'True',
> 'job': 'str', '_job_optional': 'True'
> }
> }"
>
>
> A better solution, but I don't know if it will cause trouble for
> Libvirt to parse the output.
>
> "{'_type': 'type', '_name': 'NameInfo',
> 'data': { 'job': {'_value': 'str', '_recursive': 'True'},
> 'name': {'_value': 'str', '_recursive': 'True'}
> },
> '_recursive': 'False'
> }"
>
> When we describe a DataObject (dict/list/str, one schema, extened
> schema, schema member, etc), so I we generally use a nested dictionary
> to describe a DataObject, it will split the metadata with original
> data two different dictionary level, it's convenient for parse of
> Libvirt. Here I just use a dict member as an example, actually
> it's more complex to parse all kinds of data objects.
>
> > ...
> > ;
> >
> > * Add a new type of qmp command, that returns a QString as a json literal.
> > query-qmp-schema is defined as this type. (This wouldn't be much code, but
> > may be abused in the future, I'm afraid. However we can review, limit its
> > use to introspection only)
> >
> > * And return qmp_schema_table from query-qmp-shema, which will be copied to
> > the wire.
> >
> > Feel free to disagree, it's not a perfect solution. But I really think we need
> > to avoid duplicating "enum", "base", "type", "union", "discriminator", ...
>
>
> In the past, we didn't consider to extend and add metadata by Python, so
> Libvirt wasn't happy to just get a raw schema(not extended, no metadata).
> But now, we already successfully to transfer this work to Python, and
> we can adjust to make management to be happy for the metadata and
> format.
>
> The problem is that Libvirt should parse the output twice, the json
> items are also json object string.
>
> Eric, Is it acceptabled?
>
> Example:
> * as suggested by Fam to put the metadta with schema data in same
> dict level
> * process some special cases by nested dictionary
> (eg: '*tls': 'bool' ==> 'tls': {'_value': 'bool', '_optional': 'True'} )
> * return a strList to Libvirt, the content of string is json object,
> that contains the metadata.
>
> {
> "return": [
> "{'_type': 'enum', '_name': 'ErrorClass', 'data': ['GenericError', 'CommandNotFound', 'DeviceEncrypted', 'DeviceNotActive', 'DeviceNotFound', 'KVMMissingCap'], '_recursive': 'False'}",
> "{'_type': 'command', '_name': 'add_client', 'data': {'tls': {'_value': 'bool', '_optional': 'True'}, 'skipauth': {'_value': 'bool', '_optional': 'True'}, 'protocol': 'str', 'fdname': 'str'}, '_recursive': 'False'}",
> "{'_type': 'type', '_name': 'NameInfo', 'data': {'job': {'_value': 'str', '_optional': 'True'}, 'name': {'_value': 'str', '_optional': 'True'}}, '_recursive': 'False'}",
> "{'returns': {'_type': 'type', '_recursive': 'False', 'data': {'job': {'_value': 'str', '_optional': 'True'}, 'name': {'_value': 'str', '_optional': 'True'}}, '_name': 'NameInfo'}, '_name': 'query-name', '_type': 'command', '_recursive': 'False'}",
> "......",
> "......",
> "......"
> ]
> }
Provide two txt files:
https://i-kvm.rhcloud.com/static/pub/v5/qapi-introspect.h
https://i-kvm.rhcloud.com/static/pub/v5/query-output.txt
--
Amos.
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