> From: Stephen Hemminger [mailto:[email protected]] > Sent: Friday, 16 January 2026 18.06 > > On Fri, 16 Jan 2026 11:16:21 +0000 > Morten Brørup <[email protected]> wrote: > > > buf: fix packet copy > > > > Requests for copying the at the end of a packet incorrectly returned > NULL, > > as if copying past the end of a packet. > > > > When allocating the mbuf for the copy from a mempool using pinned > external > > buffers, the external flag in this mbuf was not preserved. > > > > Fixes: c3a90c381daa ("mbuf: add a copy routine") > > > > Signed-off-by: Morten Brørup <[email protected]> > > Acked-by: Konstantin Ananyev <[email protected]> > > --- > > v2: > > * Improved comment about preserving flags for newly allocated mbuf > > potentially using pinned external buffer. > > * Added missing spaces in expression. (Stephen) > > --- > > lib/mbuf/rte_mbuf.c | 10 +++++++--- > > 1 file changed, 7 insertions(+), 3 deletions(-) > > > > diff --git a/lib/mbuf/rte_mbuf.c b/lib/mbuf/rte_mbuf.c > > index 0d931c7a15..a5d16e4c97 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; > > > > I still think asking for a copy of data that isn't there should return > NULL > not a zero length mbuf. Kind of academic since I dont think any code > uses > non-zero offset now.
Yes, I totally agree it's kind of academic. But I insist that it is an off-by-one bug, so I fixed it. Consider the function documentation: * @param offset * The number of bytes to skip before copying. * If the mbuf does not have that many bytes, it is an error * and NULL is returned. An offset resulting in copying zero bytes is not an error according to this. Also consider the comment at the comparison in the source code: /* check for request to copy at offset past end of mbuf */ It says "past the end", not "at the end"... although I'm not confident enough in my English skills to determine if this means ">=" or ">".
