RE: [PATCH v3] ip_frag: add IPv4 fragment copy packet API

["Morten Brørup" <mb@smartsharesystems.com>]

> From: Stephen Hemminger [mailto:stephen@networkplumber.org]
> Sent: Friday, 22 July 2022 16.49
> 
> On Fri, 22 Jul 2022 21:01:50 +0800
> Huichao Cai <chcchc88@163.com> wrote:
> 
> > Some NIC drivers support MBUF_FAST_FREE(Device supports optimization
> > for fast release of mbufs. When set application must guarantee that
> > per-queue all mbufs comes from the same mempool and has refcnt = 1)
> > offload. In order to adapt to this offload function, add this API.
> > Add some test data for this API.
> >
> > Signed-off-by: Huichao Cai <chcchc88@163.com>
> 
> The code should just be checking that refcnt == 1 directly.
> 
> There are cases where sender passes a cloned mbuf.  This is independent
> of the fast free optimization.
> 
> Similar to what Linux kernel does with skb_cow().

Olivier just confirmed that MBUF_FAST_FREE requires that the mbufs are direct and non-segmented, although these requirements are not yet documented.

This means that you should not generate segmented mbufs with this patch. I don't know what to do instead; probably fail with an appropriate errno.