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Re: [libvirt] [PATCH v4 4/5] qmp: full introspection support for QMP



On Mon, Jan 27, 2014 at 06:46:31PM +0800, Fam Zheng wrote:
> On Mon, 01/27 10:38, Paolo Bonzini wrote:
> > Il 27/01/2014 09:17, Amos Kong ha scritto:
> > >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 redhat com>
> > >>>---
> > >>> qapi-schema.json |  11 +++
> > >>> qmp-commands.hx  |  42 +++++++++++
> > >>> qmp.c            | 215 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
> > >>> 3 files changed, 268 insertions(+)
> > >>>
> > >>>diff --git a/qapi-schema.json b/qapi-schema.json
> > >>>index c63f0ca..6033383 100644
> > >>>--- a/qapi-schema.json
> > >>>+++ b/qapi-schema.json
> > >>>@@ -4411,3 +4411,14 @@
> > >>>     'reference-type': 'String',
> > >>>     'type': 'DataObjectType',
> > >>>     'unionobj': 'DataObjectUnion' } }
> > >>>+
> > >>>+##
> > >>>+# @query-qmp-schema
> > >>>+#
> > >>>+# Query QMP schema information
> > >>>+#
> > >>>+# @returns: list of @DataObject
> > >>>+#
> > >>>+# Since: 1.8
> > >>>+##
> > >>>+{ 'command': 'query-qmp-schema', 'returns': ['DataObject'] }
> > >>>diff --git a/qmp-commands.hx b/qmp-commands.hx
> > >>>index 02cc815..b83762d 100644
> > >>>--- a/qmp-commands.hx
> > >>>+++ b/qmp-commands.hx
> > >>>@@ -3291,6 +3291,48 @@ Example:
> > >>>    }
> > >>>
> > >>> EQMP
> > >>>+    {
> > >>>+        .name       = "query-qmp-schema",
> > >>>+        .args_type  = "",
> > >>>+        .mhandler.cmd_new = qmp_marshal_input_query_qmp_schema,
> > >>>+    },
> > >>>+
> > >>>+
> > >>>+SQMP
> > >>>+query-qmp-schema
> > >>>+----------------
> > >>>+
> > >>>+query qmp schema information
> > >>>+
> > >>>+Return a json-object with the following information:
> > >>>+
> > >>>+- "name": qmp schema name (json-string)
> > >>>+- "type": qmp schema type, it can be 'comand', 'type', 'enum', 'union'
> > >>>+- "returns": return data of qmp command (json-object, optional)
> > >>>+
> > >>>+Example:
> > >>>+
> > >>>+-> { "execute": "query-qmp-schema" }
> > >>>+-> { "return": [
> > >>>+     {
> > >>>+         "name": "query-name",
> > >>>+         "type": "command",
> > >>>+         "returns": {
> > >>>+             "name": "NameInfo",
> > >>>+             "type": "type",
> > >>>+             "data": [
> > >>>+                 {
> > >>>+                     "name": "name",
> > >>>+                     "optional": true,
> > >>>+                     "recursive": false,
> > >>>+                     "type": "str"
> > >>>+                 }
> > >>>+             ]
> > >>>+         }
> > >>>+     }
> > >>>+  }
> > >>>+
> > >>>+EQMP
> > >>>
> > >>>     {
> > >>>         .name       = "blockdev-add",
> > >>>diff --git a/qmp.c b/qmp.c
> > >>>index 0f46171..a64ae6d 100644
> > >>>--- a/qmp.c
> > >>>+++ b/qmp.c
> > >>>@@ -27,6 +27,8 @@
> > >>> #include "qapi/qmp/qobject.h"
> > >>> #include "qapi/qmp-input-visitor.h"
> > >>> #include "hw/boards.h"
> > >>>+#include "qapi/qmp/qjson.h"
> > >>>+#include "qapi-introspect.h"
> > >>>
> > >>> NameInfo *qmp_query_name(Error **errp)
> > >>> {
> > >>>@@ -488,6 +490,219 @@ CpuDefinitionInfoList *qmp_query_cpu_definitions(Error **errp)
> > >>>     return arch_query_cpu_definitions(errp);
> > >>> }
> > >>>
> > >>>+static strList *qobject_to_strlist(QObject *data)
> > >>>+{
> > >>>+    strList *list = NULL;
> > >>>+    strList **plist = &list;
> > >>>+    QList *qlist;
> > >>>+    const QListEntry *lent;
> > >>>+
> > >>>+    qlist = qobject_to_qlist(data);
> > >>>+    for (lent = qlist_first(qlist); lent; lent = qlist_next(lent)) {
> > >>>+        strList *entry = g_malloc0(sizeof(strList));
> > >>>+        entry->value = g_strdup(qobject_get_str(lent->value));
> > >>>+        *plist = entry;
> > >>>+        plist = &entry->next;
> > >>>+    }
> > >>>+
> > >>>+    return list;
> > >>>+}
> > >>>+
> > >>>+static DataObject *qobject_to_dataobj(QObject *data);
> > >>>+
> > >>>+static DataObjectMember *qobject_to_dataobjmem(QObject *data)
> > >>>+{
> > >>>+
> > >>>+    DataObjectMember *member = g_malloc0(sizeof(DataObjectMember));
> > >>>+
> > >>>+    member->type = g_malloc0(sizeof(DataObjectMemberType));
> > >>>+    if (data->type->code == QTYPE_QDICT) {
> > >>>+        member->type->kind = DATA_OBJECT_MEMBER_TYPE_KIND_EXTEND;
> > >>>+        member->type->extend = qobject_to_dataobj(data);
> > >>>+    } else {
> > >>>+        member->type->kind = DATA_OBJECT_MEMBER_TYPE_KIND_REFERENCE;
> > >>>+        member->type->reference = g_strdup(qobject_get_str(data));
> > >>>+    }
> > >>>+
> > >>>+    return member;
> > >>>+}
> > >>>+
> > >>>+static DataObjectMemberList *qobject_to_dict_memlist(QObject *data)
> > >>>+{
> > >>>+    DataObjectMemberList *list = NULL;
> > >>>+    DataObjectMemberList **plist = &list;
> > >>>+    QDict *qdict = qobject_to_qdict(data);
> > >>>+    const QDictEntry *dent;
> > >>>+
> > >>>+    for (dent = qdict_first(qdict); dent; dent = qdict_next(qdict, dent)) {
> > >>>+        DataObjectMemberList *entry = g_malloc0(sizeof(DataObjectMemberList));
> > >>>+        entry->value = qobject_to_dataobjmem(dent->value);
> > >>>+
> > >>>+        entry->value->has_optional = true;
> > >>>+        entry->value->has_name = true;
> > >>>+        if (dent->key[0] == '*') {
> > >>>+            entry->value->optional = true;
> > >>>+            entry->value->name = g_strdup(dent->key + 1);
> > >>>+        } else {
> > >>>+            entry->value->name = g_strdup(dent->key);
> > >>>+        }
> > >>>+        *plist = entry;
> > >>>+        plist = &entry->next;
> > >>>+    }
> > >>>+
> > >>>+    return list;
> > >>>+}
> > >>>+
> > >>>+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'}",
> > >        "......",
> > >        "......",
> > >        "......"
> > >    ]
> > >}
> > >
> > >>Fam
> > >
> > 
> > No, I don't like this.
> > 
> > QAPI types are perfectly able to "describe themselves", there is no need to
> > escape to JSON.
> > 
> > Let's just do what this series is doing, minus the unnecessary recursion.
> > 
> 
> I think the interface is fine with v4, no need to change to string array. It's
> just the implementation in this series shows some duplication:
 
The V4 output is very close to original conclusion about DataObject/metadata.

>                   generator in python                         parser in C
> qapi-schema.json ----------------------> qapi-introspect.h ------------------> qmp result
> 
> When you look at "qmp result", it is qapi-schema.json rewritten in a formal
> syntax (a real schema?). But when you look at qapi-introspect.h, that is
> generated by python and parsed by C, it's a schema of the qapi-schema. So the
> python code and the C code, on the arrows, are just (to a big degree) reversal
> to each other, as they both implement the "schema's schema" logic: one for
> generation and the other for parsing. They both write code for each type like
> "command", "union", "discriminator", etc.

Right, we can't avoid the duplicate if we want to connect multiple
interfaces (Python, QMP, QAPI, JSON).
 
> My question is why is this generate-and-parse necessary?

It's request of Libvirt, actually we can directly return the raw
schema to Libvirt without extending/parsing, then Libvirt parse
by itself.

> Will it be reused in the future?

It seems not.

> Can we achieve it with less duplication?
> 
> Fam

Let's see the feedback of Eric.

Thanks, Amos


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