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From: Juan Quintela <quintela@redhat.com>
In-Reply-To: <20100321195700.GB13355@redhat.com> (Michael S. Tsirkin's message
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Date: Mon, 22 Mar 2010 02:13:48 +0100
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Subject: [Qemu-devel] Re: [PATCH 0/9] Virtio cleanups
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: qemu-devel@nongnu.org

"Michael S. Tsirkin" <mst@redhat.com> wrote:
> On Sun, Mar 21, 2010 at 06:11:43PM +0000, Jamie Lokier wrote:
>> Michael S. Tsirkin wrote:
>> > That's version 1 of my patch. Version 2 removed even need for macro
>> > completely by moving allocations to the caller.
>> 
>> The downside of moving allocations are: (1) it's one more call in the
>> caller, to allocate the type, (2) it needs a virtual destructor for
>> each type to free the object, which can clutter the code if there is
>> no other reason for virtual destructors.
>
> BTW I don't understand why do you refer to virtual destructors here.
> When virtio-net.c allocates and frees structure of type VirtIONet
> this is analogous to regular destructur, not a virtual one.

If you remove it in virtio-net.c, you are right.
If your remove it in virtio.c, then you need the equivalent of a virtual
destructor (somehow you need to find a field that is an offset and do a
free(pointer- offset).

If struct VirtIODevice is the 1st field of everything, then a simple
free(pointer) is enough and does the right thing.

Notice that as just now there is no free call, you can put it in either
place.

>> I don't think those are necessarily bad, but they can remove from the
>> neatness of existing code.  Personally I favour an occasional macro
>> using sizeof/offsetof/container_of if the result is a natural and
>> sensible API to all of its callers.
>> 
>> -- Jamie

Later, Juan.