Re: [PATCH v2] mbuf: fix packet copy

Stephen Hemminger
2026-01-16T17:06:24Z

On Fri, 16 Jan 2026 11:16:21 +0000
Morten Brørup <mb@smartsharesystems.com> 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 <mb@smartsharesystems.com>
> Acked-by: Konstantin Ananyev <konstantin.ananyev@huawei.com>
> ---
> 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.