Re: [Qemu-devel] [PATCH v11 10/24] qapi: Unbox base members

[Eric Blake]

On 10/27/2015 01:52 AM, Markus Armbruster wrote:
> Eric Blake <address@hidden> writes:
> 
>> Rather than storing a base class as a pointer to a box, just
>> store the fields of that base class in the same order, so that
>> a child struct can be directly cast to its parent.  This gives
>> less malloc overhead, less pointer dereferencing, and even less
>> generated code.  Compare to the earlier commit 1e6c1616a "qapi:
>> Generate a nicer struct for flat unions" (although that patch
>> had fewer places to change, as less of qemu was directly using
>> qapi structs for flat unions).  It also allows us to turn on
>> automatic type-safe wrappers for upcasting to the base class
>> of a struct.
>>
>> Changes to the generated code look like this in qapi-types.h:
>>
>> | struct SpiceChannel {
>> |-    SpiceBasicInfo *base;
>> |+    /* Members inherited from SpiceBasicInfo: */
>> |+    char *host;
>> |+    char *port;
>> |+    NetworkAddressFamily family;
>> |+    /* Own members: */
>> |     int64_t connection_id;
>>
>> as well as added upcast functions like qapi_SpiceChannel_base().
> 
> "additional upcast functions" sounds better to my ears.

Indeed.

> 
> Patch looks good.  I can touch up the commit message in my tree.

Yay - looks like we won't need a v12.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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