Re: [Qemu-devel] [PATCH v6 16/16] qapi: Share gen_visit_fields()

[Markus Armbruster]

Eric Blake <address@hidden> writes:

> Consolidate the code between visit, command marshalling, and
> event generation that iterates over the members of a struct.
> It reduces code duplication in the generator, so that a future
> patch can reduce the size of generated code while touching only
> one instead of three locations.
>
> There are no changes to generated marshal code.
>
> The visitor code is slightly more verbose, but semantically

Suggest "becomes slightly more verbose".

> equivalent, and actually easier to read as it follows a more
> common idiom:
>
> |     visit_optional(v, &(*obj)->has_device, "device", &err);
> |-    if (!err && (*obj)->has_device) {
> |-        visit_type_str(v, &(*obj)->device, "device", &err);
> |-    }
> |     if (err) {
> |         goto out;
> |     }
> |+    if ((*obj)->has_device) {
> |+        visit_type_str(v, &(*obj)->device, "device", &err);
> |+        if (err) {
> |+            goto out;
> |+        }
> |+    }
>
> The event code is slightly more verbose, but arguably a bug
> fix (although the visitors are not well documented, use of an
> optional member should not be attempted unless guarded by a
> prior call to visit_optional()) - we were lucky that the output
> qmp visitor has a no-op visit_optional():

Suggest "becomes slightly more verbose, but this is arguably a bug fix:
although [...] prior call to visit_optional().  Works only because the
output qmp visitor [...]".

>
> |+    visit_optional(v, &has_offset, "offset", &err);
> |+    if (err) {
> |+        goto out;
> |+    }
> |     if (has_offset) {
> |         visit_type_int(v, &offset, "offset", &err);
>
> Signed-off-by: Eric Blake <address@hidden>
>
> ---
> v6: retitle 10/46, split gen_err_check() to its own patch,
> improve commit message, use named parameters in gen_visit_fields()
> to minimize effort of callers

Interdiff to v5 looks sane.