Commit 50f2bdc7 authored by Kevin Wolf's avatar Kevin Wolf
Browse files

qapi: Flat unions with arbitrary discriminator 



Instead of the rather verbose syntax that distinguishes base and
subclass fields...

  { "type": "file",
    "read-only": true,
    "data": {
        "filename": "test"
    } }

...we can now have both in the same namespace, allowing a more direct
mapping of the command line, and moving fields between the common base
and subclasses without breaking the API:

  { "driver": "file",
    "read-only": true,
    "filename": "test" }

Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
Reviewed-by: default avatarEric Blake <eblake@redhat.com>
parent 761d524d

docs/qapi-code-gen.txt

+22 −0
Original line number Diff line number Diff line
@@ -103,6 +103,28 @@ And it looks like this on the wire: 
   "data" : { "backing-file": "/some/place/my-image",

              "lazy-refcounts": true } }





Flat union types avoid the nesting on the wire. They are used whenever a

specific field of the base type is declared as the discriminator ('type' is

then no longer generated). The discriminator must always be a string field.

The above example can then be modified as follows:



 { 'type': 'BlockdevCommonOptions',

   'data': { 'driver': 'str', 'readonly': 'bool' } }

 { 'union': 'BlockdevOptions',

   'base': 'BlockdevCommonOptions',

   'discriminator': 'driver',

   'data': { 'raw': 'RawOptions',

             'qcow2': 'Qcow2Options' } }



Resulting in this JSON object:



 { "driver": "qcow2",

   "readonly": false,

   "backing-file": "/some/place/my-image",

   "lazy-refcounts": true }





=== Commands ===



Commands are defined by using a list containing three members.  The first

scripts/qapi-types.py

+9 −2
Original line number Diff line number Diff line
@@ -154,7 +154,9 @@ def generate_union(expr): 


    name = expr['union']

    typeinfo = expr['data']



    base = expr.get('base')

    discriminator = expr.get('discriminator')



    ret = mcgen('''

struct %(name)s
@@ -177,8 +179,13 @@ struct %(name)s 
''')



    if base:

        struct = find_struct(base)

        ret += generate_struct_fields(struct['data'])

        base_fields = find_struct(base)['data']

        if discriminator:

            base_fields = base_fields.copy()

            del base_fields[discriminator]

        ret += generate_struct_fields(base_fields)

    else:

        assert not discriminator



    ret += mcgen('''

};

scripts/qapi-visit.py

+67 −23
Original line number Diff line number Diff line
@@ -17,8 +17,30 @@ import os 
import getopt

import errno



def generate_visit_struct_fields(field_prefix, members):

def generate_visit_struct_fields(name, field_prefix, fn_prefix, members):

    substructs = []

    ret = ''

    full_name = name if not fn_prefix else "%s_%s" % (name, fn_prefix)



    for argname, argentry, optional, structured in parse_args(members):

        if structured:

            if not fn_prefix:

                nested_fn_prefix = argname

            else:

                nested_fn_prefix = "%s_%s" % (fn_prefix, argname)



            nested_field_prefix = "%s%s." % (field_prefix, argname)

            ret += generate_visit_struct_fields(name, nested_field_prefix,

                                                nested_fn_prefix, argentry)



    ret += mcgen('''



static void visit_type_%(full_name)s_fields(Visitor *m, %(name)s ** obj, Error **errp)

{

    Error *err = NULL;

''',

        name=name, full_name=full_name)

    push_indent()



    for argname, argentry, optional, structured in parse_args(members):

        if optional:
@@ -31,7 +53,7 @@ if (obj && (*obj)->%(prefix)shas_%(c_name)s) { 
            push_indent()



        if structured:

            ret += generate_visit_struct_body(field_prefix + argname, argname, argentry)

            ret += generate_visit_struct_body(full_name, argname, argentry)

        else:

            ret += mcgen('''

visit_type_%(type)s(m, obj ? &(*obj)->%(c_prefix)s%(c_name)s : NULL, "%(name)s", &err);
@@ -47,6 +69,12 @@ visit_type_%(type)s(m, obj ? &(*obj)->%(c_prefix)s%(c_name)s : NULL, "%(name)s", 
visit_end_optional(m, &err);

''')



    pop_indent()

    ret += mcgen('''



    error_propagate(errp, err);

}

''')

    return ret
@@ -56,8 +84,9 @@ if (!error_is_set(errp)) { 
''')

    push_indent()



    full_name = name if not field_prefix else "%s_%s" % (field_prefix, name)



    if len(field_prefix):

        field_prefix = field_prefix + "."

        ret += mcgen('''

Error **errp = &err; /* from outer scope */

Error *err = NULL;
@@ -74,19 +103,13 @@ visit_start_struct(m, (void **)obj, "%(name)s", name, sizeof(%(name)s), &err); 
    ret += mcgen('''

if (!err) {

    if (!obj || *obj) {

''')

    push_indent()

    push_indent()



    ret += generate_visit_struct_fields(field_prefix, members)

    pop_indent()

    ret += mcgen('''

        visit_type_%(name)s_fields(m, obj, &err);

        error_propagate(errp, err);

        err = NULL;

    }

''')

''',

        name=full_name)



    pop_indent()

    pop_indent()

    ret += mcgen('''

        /* Always call end_struct if start_struct succeeded.  */
@@ -98,7 +121,9 @@ if (!err) { 
    return ret



def generate_visit_struct(name, members):

    ret = mcgen('''

    ret = generate_visit_struct_fields(name, "", "", members)



    ret += mcgen('''



void visit_type_%(name)s(Visitor *m, %(name)s ** obj, const char *name, Error **errp)

{
@@ -157,9 +182,17 @@ def generate_visit_union(expr): 
    members = expr['data']



    base = expr.get('base')

    discriminator = expr.get('discriminator')



    ret = generate_visit_enum('%sKind' % name, members.keys())



    if base:

        base_fields = find_struct(base)['data']

        if discriminator:

            base_fields = base_fields.copy()

            del base_fields[discriminator]

        ret += generate_visit_struct_fields(name, "", "", base_fields)



    ret += mcgen('''



void visit_type_%(name)s(Visitor *m, %(name)s ** obj, const char *name, Error **errp)
@@ -179,23 +212,34 @@ void visit_type_%(name)s(Visitor *m, %(name)s ** obj, const char *name, Error ** 
    push_indent()



    if base:

        struct = find_struct(base)

        push_indent()

        ret += generate_visit_struct_fields("", struct['data'])

        pop_indent()

        ret += mcgen('''

    visit_type_%(name)s_fields(m, obj, &err);

''',

            name=name)



    pop_indent()

    ret += mcgen('''

        visit_type_%(name)sKind(m, &(*obj)->kind, "type", &err);

        visit_type_%(name)sKind(m, &(*obj)->kind, "%(type)s", &err);

        if (!err) {

            switch ((*obj)->kind) {

''',

                 name=name)

                 name=name, type="type" if not discriminator else discriminator)



    for key in members:

        if not discriminator:

            fmt = 'visit_type_%(c_type)s(m, &(*obj)->%(c_name)s, "data", &err);'

        else:

            fmt = '''visit_start_implicit_struct(m, (void**) &(*obj)->%(c_name)s, sizeof(%(c_type)s), &err);

                if (!err) {

                    visit_type_%(c_type)s_fields(m, &(*obj)->%(c_name)s, &err);

                    error_propagate(errp, err);

                    err = NULL;

                    visit_end_implicit_struct(m, &err);

                }'''



        ret += mcgen('''

            case %(abbrev)s_KIND_%(enum)s:

                visit_type_%(c_type)s(m, &(*obj)->%(c_name)s, "data", &err);

                ''' + fmt + '''

                break;

''',

                abbrev = de_camel_case(name).upper(),