[Qemu-devel] [PATCH for-2.9 v2] qom: Make all interface types abstract

[Qemu-devel] [PATCH for-2.9 v2] qom: Make all interface types abstract

[Eduardo Habkost]

"qom-list-types abstract=false" currently returns all interface
types, as if they were not abstract. Fix this by making sure all
interface types are abstract.

All interface types have instance_size == 0, so we can use
it to set abstract=true on type_initialize().

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
---
Changes v1 -> v2:
* Use old-fashioned if statement instead of "|=" on bool field
  Suggested-by: Andreas Färber <afaerber@suse.de>
* Keep "device/introspect" path prefix on unit test
  * Suggested-by: Andreas Färber <afaerber@suse.de>
---
 qom/object.c                   |  6 +++++
 tests/device-introspect-test.c | 60 +++++++++++++++++++++++++++++++++++++++---
 2 files changed, 63 insertions(+), 3 deletions(-)

diff --git a/qom/object.c b/qom/object.c
index 7a05e35..760fafb 100644
--- a/qom/object.c
+++ b/qom/object.c
@@ -272,6 +272,12 @@ static void type_initialize(TypeImpl *ti)
 
     ti->class_size = type_class_get_size(ti);
     ti->instance_size = type_object_get_size(ti);
+    /* Any type with zero instance_size is implicitly abstract.
+     * This means interface types are all abstract.
+     */
+    if (ti->instance_size == 0) {
+        ti->abstract = true;
+    }
 
     ti->class = g_malloc0(ti->class_size);
 
diff --git a/tests/device-introspect-test.c b/tests/device-introspect-test.c
index 37debc1..c5637cc 100644
--- a/tests/device-introspect-test.c
+++ b/tests/device-introspect-test.c
@@ -20,18 +20,24 @@
 #include "qemu/osdep.h"
 #include "qemu-common.h"
 #include "qapi/qmp/qstring.h"
+#include "qapi/qmp/qbool.h"
+#include "qapi/qmp/qdict.h"
 #include "libqtest.h"
 
 const char common_args[] = "-nodefaults -machine none";
 
-static QList *device_type_list(bool abstract)
+static QList *qom_list_types(const char *implements, bool abstract)
 {
     QDict *resp;
     QList *ret;
+    QDict *args = qdict_new();
 
+    qdict_put(args, "abstract", qbool_from_bool(abstract));
+    if (implements) {
+        qdict_put(args, "implements", qstring_from_str(implements));
+    }
     resp = qmp("{'execute': 'qom-list-types',"
-               " 'arguments': {'implements': 'device', 'abstract': %i}}",
-               abstract);
+               " 'arguments': %p }", args);
     g_assert(qdict_haskey(resp, "return"));
     ret = qdict_get_qlist(resp, "return");
     QINCREF(ret);
@@ -39,6 +45,11 @@ static QList *device_type_list(bool abstract)
     return ret;
 }
 
+static QList *device_type_list(bool abstract)
+{
+    return qom_list_types("device", abstract);
+}
+
 static void test_one_device(const char *type)
 {
     QDict *resp;
@@ -110,6 +121,48 @@ static void test_device_intro_concrete(void)
     qtest_end();
 }
 
+static void test_abstract_interfaces(void)
+{
+    QList *all_types;
+    QList *obj_types;
+    QListEntry *ae;
+
+    qtest_start(common_args);
+    /* qom-list-types implements=interface would return any type
+     * that implements _any_ interface (not just interface types),
+     * so use a trick to find the interface type names:
+     * - list all object types
+     * - list all types, and look for items that are not
+     *   on the first list
+     */
+    all_types = qom_list_types(NULL, false);
+    obj_types = qom_list_types("object", false);
+
+    QLIST_FOREACH_ENTRY(all_types, ae) {
+        QDict *at = qobject_to_qdict(qlist_entry_obj(ae));
+        const char *aname = qdict_get_str(at, "name");
+        QListEntry *oe;
+        const char *found = NULL;
+
+        QLIST_FOREACH_ENTRY(obj_types, oe) {
+            QDict *ot = qobject_to_qdict(qlist_entry_obj(oe));
+            const char *oname = qdict_get_str(ot, "name");
+            if (!strcmp(aname, oname)) {
+                found = oname;
+                break;
+            }
+        }
+
+        /* Using g_assert_cmpstr() will give more useful failure
+         * messages than g_assert(found) */
+        g_assert_cmpstr(aname, ==, found);
+    }
+
+    QDECREF(all_types);
+    QDECREF(obj_types);
+    qtest_end();
+}
+
 int main(int argc, char **argv)
 {
     g_test_init(&argc, &argv, NULL);
@@ -118,6 +171,7 @@ int main(int argc, char **argv)
     qtest_add_func("device/introspect/none", test_device_intro_none);
     qtest_add_func("device/introspect/abstract", test_device_intro_abstract);
     qtest_add_func("device/introspect/concrete", test_device_intro_concrete);
+    qtest_add_func("device/introspect/abstract-interfaces", test_abstract_interfaces);
 
     return g_test_run();
 }
-- 
2.7.4

Re: [Qemu-devel] [PATCH for-2.9 v2] qom: Make all interface types abstract

[Markus Armbruster]

Eduardo Habkost <ehabkost@redhat.com> writes:

> "qom-list-types abstract=false" currently returns all interface
> types, as if they were not abstract. Fix this by making sure all
> interface types are abstract.
>
> All interface types have instance_size == 0, so we can use
> it to set abstract=true on type_initialize().
>
> Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
> ---
> Changes v1 -> v2:
> * Use old-fashioned if statement instead of "|=" on bool field
>   Suggested-by: Andreas Färber <afaerber@suse.de>
> * Keep "device/introspect" path prefix on unit test
>   * Suggested-by: Andreas Färber <afaerber@suse.de>
> ---
>  qom/object.c                   |  6 +++++
>  tests/device-introspect-test.c | 60 +++++++++++++++++++++++++++++++++++++++---
>  2 files changed, 63 insertions(+), 3 deletions(-)
>
> diff --git a/qom/object.c b/qom/object.c
> index 7a05e35..760fafb 100644
> --- a/qom/object.c
> +++ b/qom/object.c
> @@ -272,6 +272,12 @@ static void type_initialize(TypeImpl *ti)
>  
>      ti->class_size = type_class_get_size(ti);
>      ti->instance_size = type_object_get_size(ti);
> +    /* Any type with zero instance_size is implicitly abstract.
> +     * This means interface types are all abstract.
> +     */
> +    if (ti->instance_size == 0) {
> +        ti->abstract = true;
> +    }
>  
>      ti->class = g_malloc0(ti->class_size);
>  

Letting zero instance_size imply abstract works (I guess), but is it
wise to imply?  Is requiring explicit .abstract = true really too much
trouble?

Consider:

    static const TypeInfo uc_interface_info = {
        .name          = TYPE_USER_CREATABLE,
        .parent        = TYPE_INTERFACE,
        .class_size = sizeof(UserCreatableClass),
    };

Is this abstract?  Yes, because there's no .instance_size = ...,
therefore .instance_size remains zero, and .abstract defaults to true.

    static const TypeInfo memory_region_info = {
        .parent             = TYPE_OBJECT,
        .name               = TYPE_MEMORY_REGION,
        .instance_size      = sizeof(MemoryRegion),
        .instance_init      = memory_region_initfn,
        .instance_finalize  = memory_region_finalize,
    };

Is this abstract?  No, because with .instance_size =
sizeof(MemoryRegion), which known to be non-zero, .abstract defaults to
false.

Is such a complex default a good idea?

   static const TypeInfo rng_backend_info = {
       .name = TYPE_RNG_BACKEND,
       .parent = TYPE_OBJECT,
       .instance_size = sizeof(RngBackend),
       .instance_init = rng_backend_init,
       .instance_finalize = rng_backend_finalize,
       .class_size = sizeof(RngBackendClass),
       .class_init = rng_backend_class_init,
       .abstract = true,
       .interfaces = (InterfaceInfo[]) {
           { TYPE_USER_CREATABLE },
           { }
       }
   };

Is this abstract?  Yes, because with .abstract = true, the default
doesn't matter.

How do you find all abstract TypeInfo in the source?  The uninitiated
might grep for .abstract = true, and be misled.  The initiated will be
annoyed instead, because grepping for *absence* of .instance_size = is
bothersome.

I suspect life could be easier going forward if we instead required
.abstract = true for interfaces, and enforced it with
assert(ti->instance_size || ti->abstract) here.

> diff --git a/tests/device-introspect-test.c b/tests/device-introspect-test.c
> index 37debc1..c5637cc 100644
> --- a/tests/device-introspect-test.c
> +++ b/tests/device-introspect-test.c
> @@ -20,18 +20,24 @@
>  #include "qemu/osdep.h"
>  #include "qemu-common.h"
>  #include "qapi/qmp/qstring.h"
> +#include "qapi/qmp/qbool.h"
> +#include "qapi/qmp/qdict.h"
>  #include "libqtest.h"
>  
>  const char common_args[] = "-nodefaults -machine none";
>  
> -static QList *device_type_list(bool abstract)
> +static QList *qom_list_types(const char *implements, bool abstract)
>  {
>      QDict *resp;
>      QList *ret;
> +    QDict *args = qdict_new();
>  
> +    qdict_put(args, "abstract", qbool_from_bool(abstract));
> +    if (implements) {
> +        qdict_put(args, "implements", qstring_from_str(implements));
> +    }
>      resp = qmp("{'execute': 'qom-list-types',"
> -               " 'arguments': {'implements': 'device', 'abstract': %i}}",
> -               abstract);
> +               " 'arguments': %p }", args);
>      g_assert(qdict_haskey(resp, "return"));
>      ret = qdict_get_qlist(resp, "return");
>      QINCREF(ret);
> @@ -39,6 +45,11 @@ static QList *device_type_list(bool abstract)
>      return ret;
>  }
>  
> +static QList *device_type_list(bool abstract)
> +{
> +    return qom_list_types("device", abstract);
> +}
> +
>  static void test_one_device(const char *type)
>  {
>      QDict *resp;
> @@ -110,6 +121,48 @@ static void test_device_intro_concrete(void)
>      qtest_end();
>  }
>  
> +static void test_abstract_interfaces(void)
> +{
> +    QList *all_types;
> +    QList *obj_types;
> +    QListEntry *ae;
> +
> +    qtest_start(common_args);
> +    /* qom-list-types implements=interface would return any type
> +     * that implements _any_ interface (not just interface types),
> +     * so use a trick to find the interface type names:
> +     * - list all object types
> +     * - list all types, and look for items that are not
> +     *   on the first list
> +     */
> +    all_types = qom_list_types(NULL, false);
> +    obj_types = qom_list_types("object", false);
> +
> +    QLIST_FOREACH_ENTRY(all_types, ae) {
> +        QDict *at = qobject_to_qdict(qlist_entry_obj(ae));
> +        const char *aname = qdict_get_str(at, "name");
> +        QListEntry *oe;
> +        const char *found = NULL;
> +
> +        QLIST_FOREACH_ENTRY(obj_types, oe) {
> +            QDict *ot = qobject_to_qdict(qlist_entry_obj(oe));
> +            const char *oname = qdict_get_str(ot, "name");
> +            if (!strcmp(aname, oname)) {
> +                found = oname;
> +                break;
> +            }
> +        }
> +
> +        /* Using g_assert_cmpstr() will give more useful failure
> +         * messages than g_assert(found) */

Sure this comment is worth having?

> +        g_assert_cmpstr(aname, ==, found);

I'm having a mental block...  what exactly is this loop nest testing?

> +    }
> +
> +    QDECREF(all_types);
> +    QDECREF(obj_types);
> +    qtest_end();
> +}
> +
>  int main(int argc, char **argv)
>  {
>      g_test_init(&argc, &argv, NULL);
> @@ -118,6 +171,7 @@ int main(int argc, char **argv)
>      qtest_add_func("device/introspect/none", test_device_intro_none);
>      qtest_add_func("device/introspect/abstract", test_device_intro_abstract);
>      qtest_add_func("device/introspect/concrete", test_device_intro_concrete);
> +    qtest_add_func("device/introspect/abstract-interfaces", test_abstract_interfaces);
>  
>      return g_test_run();
>  }

Re: [Qemu-devel] [PATCH for-2.9 v2] qom: Make all interface types abstract

[Eduardo Habkost]

On Wed, Dec 14, 2016 at 02:04:50PM +0100, Markus Armbruster wrote:
> Eduardo Habkost <ehabkost@redhat.com> writes:
> 
> > "qom-list-types abstract=false" currently returns all interface
> > types, as if they were not abstract. Fix this by making sure all
> > interface types are abstract.
> >
> > All interface types have instance_size == 0, so we can use
> > it to set abstract=true on type_initialize().
> >
> > Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
> > ---
> > Changes v1 -> v2:
> > * Use old-fashioned if statement instead of "|=" on bool field
> >   Suggested-by: Andreas Färber <afaerber@suse.de>
> > * Keep "device/introspect" path prefix on unit test
> >   * Suggested-by: Andreas Färber <afaerber@suse.de>
> > ---
> >  qom/object.c                   |  6 +++++
> >  tests/device-introspect-test.c | 60 +++++++++++++++++++++++++++++++++++++++---
> >  2 files changed, 63 insertions(+), 3 deletions(-)
> >
> > diff --git a/qom/object.c b/qom/object.c
> > index 7a05e35..760fafb 100644
> > --- a/qom/object.c
> > +++ b/qom/object.c
> > @@ -272,6 +272,12 @@ static void type_initialize(TypeImpl *ti)
> >  
> >      ti->class_size = type_class_get_size(ti);
> >      ti->instance_size = type_object_get_size(ti);
> > +    /* Any type with zero instance_size is implicitly abstract.
> > +     * This means interface types are all abstract.
> > +     */
> > +    if (ti->instance_size == 0) {
> > +        ti->abstract = true;
> > +    }
> >  
> >      ti->class = g_malloc0(ti->class_size);
> >  
> 
> Letting zero instance_size imply abstract works (I guess), but is it
> wise to imply?  Is requiring explicit .abstract = true really too much
> trouble?
> 
> Consider:
> 
>     static const TypeInfo uc_interface_info = {
>         .name          = TYPE_USER_CREATABLE,
>         .parent        = TYPE_INTERFACE,
>         .class_size = sizeof(UserCreatableClass),
>     };
> 
> Is this abstract?  Yes, because there's no .instance_size = ...,
> therefore .instance_size remains zero, and .abstract defaults to true.
> 
>     static const TypeInfo memory_region_info = {
>         .parent             = TYPE_OBJECT,
>         .name               = TYPE_MEMORY_REGION,
>         .instance_size      = sizeof(MemoryRegion),
>         .instance_init      = memory_region_initfn,
>         .instance_finalize  = memory_region_finalize,
>     };
> 
> Is this abstract?  No, because with .instance_size =
> sizeof(MemoryRegion), which known to be non-zero, .abstract defaults to
> false.

Let's make it worse:

static const TypeInfo palmetto_bmc_type = {
    .name = MACHINE_TYPE_NAME("palmetto-bmc"),
    .parent = TYPE_MACHINE,
    .class_init = palmetto_bmc_class_init,
};

Is this abstract? No, because instance_size from the parent type is used, and
it is not zero.

> 
> Is such a complex default a good idea?
> 
>    static const TypeInfo rng_backend_info = {
>        .name = TYPE_RNG_BACKEND,
>        .parent = TYPE_OBJECT,
>        .instance_size = sizeof(RngBackend),
>        .instance_init = rng_backend_init,
>        .instance_finalize = rng_backend_finalize,
>        .class_size = sizeof(RngBackendClass),
>        .class_init = rng_backend_class_init,
>        .abstract = true,
>        .interfaces = (InterfaceInfo[]) {
>            { TYPE_USER_CREATABLE },
>            { }
>        }
>    };
> 
> Is this abstract?  Yes, because with .abstract = true, the default
> doesn't matter.
> 
> How do you find all abstract TypeInfo in the source?  The uninitiated
> might grep for .abstract = true, and be misled.  The initiated will be
> annoyed instead, because grepping for *absence* of .instance_size = is
> bothersome.
> 
> I suspect life could be easier going forward if we instead required
> .abstract = true for interfaces, and enforced it with
> assert(ti->instance_size || ti->abstract) here.

I was doing that before deciding to change type_initialize(). I
think I still have the commit in my git reflog, I will recover it
and submit it as v3.

[...]
> > +static void test_abstract_interfaces(void)
> > +{
> > +    QList *all_types;
> > +    QList *obj_types;
> > +    QListEntry *ae;
> > +
> > +    qtest_start(common_args);
> > +    /* qom-list-types implements=interface would return any type
> > +     * that implements _any_ interface (not just interface types),
> > +     * so use a trick to find the interface type names:
> > +     * - list all object types
> > +     * - list all types, and look for items that are not
> > +     *   on the first list
> > +     */
> > +    all_types = qom_list_types(NULL, false);
> > +    obj_types = qom_list_types("object", false);
> > +
> > +    QLIST_FOREACH_ENTRY(all_types, ae) {
> > +        QDict *at = qobject_to_qdict(qlist_entry_obj(ae));
> > +        const char *aname = qdict_get_str(at, "name");
> > +        QListEntry *oe;
> > +        const char *found = NULL;
> > +
> > +        QLIST_FOREACH_ENTRY(obj_types, oe) {
> > +            QDict *ot = qobject_to_qdict(qlist_entry_obj(oe));
> > +            const char *oname = qdict_get_str(ot, "name");
> > +            if (!strcmp(aname, oname)) {
> > +                found = oname;
> > +                break;
> > +            }
> > +        }
> > +
> > +        /* Using g_assert_cmpstr() will give more useful failure
> > +         * messages than g_assert(found) */
> 
> Sure this comment is worth having?

All we need to check here is if 'found' is not NULL. I think I
would be confused by the usage of g_assert_cmpstr() if I was
reading the code, so I decided to add the comment.

> 
> > +        g_assert_cmpstr(aname, ==, found);
> 
> I'm having a mental block...  what exactly is this loop nest testing?

It's implementing the trick described above:
1) list all object types
2) list all types, and look for items that are not on the first
   list.

In other words, checking if all items in all_types are present in
obj_types.

My first attempt was to just check if
  qom-list-types implements="interface" abstract=false
returned an empty list, but it failed because it returns all
object types that implement any interface.

-- 
Eduardo

Re: [Qemu-devel] [PATCH for-2.9 v2] qom: Make all interface types abstract

[Paolo Bonzini]

On 14/12/2016 14:48, Eduardo Habkost wrote:
>> How do you find all abstract TypeInfo in the source?  The uninitiated
>> might grep for .abstract = true, and be misled.  The initiated will be
>> annoyed instead, because grepping for *absence* of .instance_size = is
>> bothersome.
>>
>> I suspect life could be easier going forward if we instead required
>> .abstract = true for interfaces, and enforced it with
>> assert(ti->instance_size || ti->abstract) here.
> I was doing that before deciding to change type_initialize(). I
> think I still have the commit in my git reflog, I will recover it
> and submit it as v3.

I think it's worse.

Interfaces are abstract by definition.  Requiring ".abstract = true"
makes things less intuitive.  v2 seems good.

Paolo

Re: [Qemu-devel] [PATCH for-2.9 v2] qom: Make all interface types abstract

[Eduardo Habkost]

On Wed, Dec 14, 2016 at 06:07:48PM +0100, Paolo Bonzini wrote:
> 
> 
> On 14/12/2016 14:48, Eduardo Habkost wrote:
> >> How do you find all abstract TypeInfo in the source?  The uninitiated
> >> might grep for .abstract = true, and be misled.  The initiated will be
> >> annoyed instead, because grepping for *absence* of .instance_size = is
> >> bothersome.
> >>
> >> I suspect life could be easier going forward if we instead required
> >> .abstract = true for interfaces, and enforced it with
> >> assert(ti->instance_size || ti->abstract) here.
> > I was doing that before deciding to change type_initialize(). I
> > think I still have the commit in my git reflog, I will recover it
> > and submit it as v3.
> 
> I think it's worse.
> 
> Interfaces are abstract by definition.  Requiring ".abstract = true"
> makes things less intuitive.  v2 seems good.

I don't think that making the type declaration more explicit
would cause any real problems, and it would help people grepping
the code. Anybody forgetting to add .abstract=true to new
interfaces would immediatly see an assertion error and would just
be annoyed for 1 minute.

I will submit v3 and let the maintainers decide.

-- 
Eduardo

Re: [Qemu-devel] [PATCH for-2.9 v2] qom: Make all interface types abstract

[Markus Armbruster]

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 14/12/2016 14:48, Eduardo Habkost wrote:
>>> How do you find all abstract TypeInfo in the source?  The uninitiated
>>> might grep for .abstract = true, and be misled.  The initiated will be
>>> annoyed instead, because grepping for *absence* of .instance_size = is
>>> bothersome.
>>>
>>> I suspect life could be easier going forward if we instead required
>>> .abstract = true for interfaces, and enforced it with
>>> assert(ti->instance_size || ti->abstract) here.
>> I was doing that before deciding to change type_initialize(). I
>> think I still have the commit in my git reflog, I will recover it
>> and submit it as v3.
>
> I think it's worse.
>
> Interfaces are abstract by definition.  Requiring ".abstract = true"
> makes things less intuitive.  v2 seems good.

What makes a TypeInfo declaration an interface?  Whatever it is, it
better be *locally* obvious.

Re: [Qemu-devel] [PATCH for-2.9 v2] qom: Make all interface types abstract

[Paolo Bonzini]

On 14/12/2016 18:47, Markus Armbruster wrote:
> Paolo Bonzini <pbonzini@redhat.com> writes:
> 
>> On 14/12/2016 14:48, Eduardo Habkost wrote:
>>>> How do you find all abstract TypeInfo in the source?  The uninitiated
>>>> might grep for .abstract = true, and be misled.  The initiated will be
>>>> annoyed instead, because grepping for *absence* of .instance_size = is
>>>> bothersome.
>>>>
>>>> I suspect life could be easier going forward if we instead required
>>>> .abstract = true for interfaces, and enforced it with
>>>> assert(ti->instance_size || ti->abstract) here.
>>> I was doing that before deciding to change type_initialize(). I
>>> think I still have the commit in my git reflog, I will recover it
>>> and submit it as v3.
>>
>> I think it's worse.
>>
>> Interfaces are abstract by definition.  Requiring ".abstract = true"
>> makes things less intuitive.  v2 seems good.
> 
> What makes a TypeInfo declaration an interface?  Whatever it is, it
> better be *locally* obvious.

The fact that the superclass is an interface:

1) most interface names are (or should be) "interfacey".  Compare
device, memory backend, console (all classes) with user-creatable, fw
path provider, hotplug handler.  A few others simply end with "_IF".  Of
course naming is the hardest problem in computer science so there are
some interfaces whose name might apply just as well to a class (stream
slave, ISA DMA).  However...

2) ... currently we don't have a single case of an interface that
doesn't inherit from TYPE_INTERFACE, so all interfaces are declared with
".parent = TYPE_INTERFACE".  That does make a TypeInfo obviously an
interface.

If we ever have a case of interface inheritance, the supertype had
better have a good name.

Paolo

Re: [Qemu-devel] [PATCH for-2.9 v2] qom: Make all interface types abstract

[Markus Armbruster]

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 14/12/2016 18:47, Markus Armbruster wrote:
>> Paolo Bonzini <pbonzini@redhat.com> writes:
>> 
>>> On 14/12/2016 14:48, Eduardo Habkost wrote:
>>>>> How do you find all abstract TypeInfo in the source?  The uninitiated
>>>>> might grep for .abstract = true, and be misled.  The initiated will be
>>>>> annoyed instead, because grepping for *absence* of .instance_size = is
>>>>> bothersome.
>>>>>
>>>>> I suspect life could be easier going forward if we instead required
>>>>> .abstract = true for interfaces, and enforced it with
>>>>> assert(ti->instance_size || ti->abstract) here.
>>>> I was doing that before deciding to change type_initialize(). I
>>>> think I still have the commit in my git reflog, I will recover it
>>>> and submit it as v3.
>>>
>>> I think it's worse.
>>>
>>> Interfaces are abstract by definition.  Requiring ".abstract = true"
>>> makes things less intuitive.  v2 seems good.
>> 
>> What makes a TypeInfo declaration an interface?  Whatever it is, it
>> better be *locally* obvious.
>
> The fact that the superclass is an interface:
>
> 1) most interface names are (or should be) "interfacey".  Compare
> device, memory backend, console (all classes) with user-creatable, fw
> path provider, hotplug handler.  A few others simply end with "_IF".  Of
> course naming is the hardest problem in computer science so there are
> some interfaces whose name might apply just as well to a class (stream
> slave, ISA DMA).  However...
>
> 2) ... currently we don't have a single case of an interface that
> doesn't inherit from TYPE_INTERFACE, so all interfaces are declared with
> ".parent = TYPE_INTERFACE".  That does make a TypeInfo obviously an
> interface.
>
> If we ever have a case of interface inheritance, the supertype had
> better have a good name.

I see.

The choice is between a complex default for .abstract that permits us to
elide .abstract = true for interface types, and a simple default that
requires us to spell it out explicitly.

Given that we have the grand total of thirteen interface types, I prefer
simple & explicit.  Thirteen obvious .abstract = true are less of a
mental burden than a complex default.  Even 25 would be for me.