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Date: Mon, 22 Mar 2010 10:37:58 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: [Qemu-devel] Re: [PATCH 0/9] Virtio cleanups
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To: Juan Quintela <quintela@redhat.com>
Cc: qemu-devel@nongnu.org

On Mon, Mar 22, 2010 at 02:13:48AM +0100, Juan Quintela wrote:
> "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.

We should remove it in virtio-net.c. We need to do cleanup there anyway.

> 
> >> 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.