RE: [PATCH] mbuf: fix packet copy

Konstantin Ananyev
2026-01-11T15:19:48Z

>
> PING for review.
>
> > From: Morten Brørup [mailto:mb@smartsharesystems.com]
> > Sent: Wednesday, 19 November 2025 13.04
> >
> > Requests for copying the at the end of a packet incorrectly returned
> > NULL,
> > as if copying past the end of a packet.
> >
> > When allocating copies from a mempool using pinned external buffers,
> > the
> > external flag was not preserved in these mbufs.
> >
> > Fixes: c3a90c381daa ("mbuf: add a copy routine")
> >
> > Signed-off-by: Morten Brørup <mb@smartsharesystems.com>
> > ---
> > lib/mbuf/rte_mbuf.c | 6 +++---
> > 1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/lib/mbuf/rte_mbuf.c b/lib/mbuf/rte_mbuf.c
> > index 0d931c7a15..e639aff03e 100644
> > --- a/lib/mbuf/rte_mbuf.c
> > +++ b/lib/mbuf/rte_mbuf.c
> > @@ -675,7 +675,7 @@ rte_pktmbuf_copy(const struct rte_mbuf *m, struct
> > rte_mempool *mp,
> > __rte_mbuf_sanity_check(m, 1);
> >
> > /* check for request to copy at offset past end of mbuf */
> > - if (unlikely(off >= m->pkt_len))
> > + if (unlikely(off > m->pkt_len))
> > return NULL;

So, when off= m->pkt_len, what do we want it to return?
New mbuf with pkt_len == 0?
Any point of such copying then?

> > mc = rte_pktmbuf_alloc(mp);
> > @@ -688,8 +688,8 @@ rte_pktmbuf_copy(const struct rte_mbuf *m, struct
> > rte_mempool *mp,
> >
> > __rte_pktmbuf_copy_hdr(mc, m);
> >
> > - /* copied mbuf is not indirect or external */
> > - mc->ol_flags = m->ol_flags &
> > ~(RTE_MBUF_F_INDIRECT|RTE_MBUF_F_EXTERNAL);
> > + /* copy flags except indirect and external, and preserve flags of
> > newly allocated mbuf */
> > + mc->ol_flags |= m->ol_flags &
> > ~(RTE_MBUF_F_INDIRECT|RTE_MBUF_F_EXTERNAL);

Which flags in the new mbuf we want to preserve?
AFAIK mbuf_alloc() doesn't set any flags.
BTW, if there are some flags that we would like to preserve,
wouldn't that be a change in public API behavior?

> >
> > prev = &mc->next;
> > m_last = mc;
> > --
> > 2.43.0