Re: [Qemu-devel] [PATCH RFC 2/2] qmp: New command qom-new

[Igor Mammedov]

On 05/24/2012 03:04 PM, Anthony Liguori wrote:

On 05/24/2012 06:43 AM, Markus Armbruster wrote:

To create objects via QMP.

Test case:

$ upstream-qemu --enable-kvm -S -m 384 -vnc :0 -monitor stdio -chardev 
socket,id=qmp,path=test-qmp,server=on,wait=off -mon mode=control,chardev=qmp

Conversation on the qmp socket:
{"QMP": {"version": {"qemu": {"micro": 93, "minor": 0, "major": 1}, "package": ""}, 
"capabilities": []}}
{ "execute": "qmp_capabilities" }
{"return": {}}
{"execute":"qom-new","arguments":{"parent":"/xxx", "prop-name":"test-qmp-new", 
"type-name":"xxx"}}
{"error": {"class": "DeviceNotFound", "desc": "Device '/xxx' not found", "data": 
{"device": "/xxx"}}}
{"execute":"qom-new","arguments":{"parent":"/machine", "prop-name":"test-qmp-new", 
"type-name":"xxx"}}
{"error": {"class": "InvalidParameterValue", "desc": "Parameter 'type-name' expects a type name", "data": 
{"name": "type-name", "expected": "a type
name"}}}
{"execute":"qom-new","arguments":{"parent":"/machine", "prop-name":"test-qmp-new", 
"type-name":"container"}}
{"return": "/machine/test-qmp-new"}
{"execute":"qom-list","arguments":{"path":"/machine"}}
{"return": [{"name": "test-qmp-new", "type": "child<container>"}, {"name": "i440fx", "type": 
"child<i440FX-pcihost>"}, {"name": "unattached",
"type": "child<container>"}, {"name": "peripheral", "type": "child<container>"}, {"name": 
"peripheral-anon", "type": "child<container>"}]}

Note: qdev objects (subtype of TYPE_DEVICE) created with qom-new lack
additional magic performed by qdev_try_create(), and almost certainly
won't work.

Signed-off-by: Markus Armbruster<arm...@redhat.com>
---
qapi-schema.json | 22 ++++++++++++++++++++++
qmp-commands.hx | 5 +++++
qmp.c | 27 +++++++++++++++++++++++++++
3 files changed, 54 insertions(+), 0 deletions(-)

diff --git a/qapi-schema.json b/qapi-schema.json
index 2ca7195..ab9e68b 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -1699,6 +1699,28 @@
'returns': [ 'ObjectTypeInfo' ] }

##
+# qom-new:
+#
+# Create a new object
+#
+# @parent: the parent's path within the object model. See @qom-get
+# for a description of paths.
+#
+# @prop-name: the name of the property to add to the parent.
+#
+# @type: the new object's type name
+#
+# Returns: The new object's canonical absolute path
+#
+# Since: 1.2
+#
+# Notes: This command is experimental and may change syntax in future releases.
+##
+{ 'command': 'qom-new',
+ 'data': { 'parent': 'str', 'prop-name': 'str', 'type-name': 'str' },
+ 'returns': 'str' }
+
+##
# @migrate
#
# Migrates the current running guest to another Virtual Machine.
diff --git a/qmp-commands.hx b/qmp-commands.hx
index db980fa..53adda2 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -2142,3 +2142,8 @@ EQMP
.args_type = "implements:s?,abstract:b?",
.mhandler.cmd_new = qmp_marshal_input_qom_list_types,
},
+ {
+ .name = "qom-new",
+ .args_type = "parent:s,prop-name:s,type-name:s",
+ .mhandler.cmd_new = qmp_marshal_input_qom_new,
+ },
diff --git a/qmp.c b/qmp.c
index fee9fb2..cad5610 100644
--- a/qmp.c
+++ b/qmp.c
@@ -417,3 +417,30 @@ ObjectTypeInfoList *qmp_qom_list_types(bool has_implements,

return ret;
}
+
+char *qmp_qom_new(const char *parent, const char *prop_name,
+ const char *type_name, Error **errp)
+{
+ Object *p, *obj;
+ Type type;
+
+ // TODO anything fancy with containger_get() needed?

I'm not sure how I feel about this. I never intended for a user to be able to 
create objects that were arbitrary children of other objects.

In some ways, I think this is almost too powerful of an interface to expose to 
users. I like things like device_add() better that only creates objects
of TYPE_DEVICE that are always in /peripherial.

For block, we'd have a similar interface that always created objects of 
TYPE_BLOCK_DRIVER and put them in /block.

Will we have a special cases for every incompatible device types that is going 
to be hot-plugged via device_add monitor command?

For CPUs my thoughts were moving in opposite direction, like:
 - make possible to create and initialize CPU as a regular QOM object
 - hack qdev_device_add() to allow not only TYPE_DEVICE to be created there

There are patches out there that make cpu a child of /machine at board level.
But for hot-added objects parent could be specified as a property
or knowledge about parent hard-coded inside of object itself or
hard-coded in device_add().
Which one of them likely to be adopted?

+ p = object_resolve_path(parent, NULL);
+ if (!p) {
+ error_set(errp, QERR_DEVICE_NOT_FOUND, parent);
+ return NULL;
+ }
+
+ type = type_get_by_name(type_name);
+ if (!type) {
+ error_set(errp, QERR_INVALID_PARAMETER_VALUE,
+ "type-name", "a type name");
+ return NULL;
+ }
+ obj = object_new_with_type(type);
+
+ // TODO bombs if p is an interface object; can this happen?

All interface types have .abstract set and there's an assert() to validate that 
an object isn't abstract when creating. So it should be
object_new_with_type() that's asserting, not object_property_add_child.

We'll probably want to enforce that qom-new isn't given an abstract type by 
introducing a type_is_abstract() or something like that.

Regards,

Anthony Liguori

+ object_property_add_child(p, prop_name, obj, NULL);
+
+ return object_get_canonical_path(obj);
+}

--
-----
 Igor