Re: [dpdk-dev] [PATCH v3 4/6] mbuf: add a pktmbuf copy routine

[Andrew Rybchenko <arybchenko@solarflare.com>]

On 9/30/19 10:20 PM, Stephen Hemminger wrote:
> This is a commonly used operation that surprisingly the
> DPDK has not supported. The new rte_pktmbuf_copy does a
> deep copy of packet. This is a complete copy including
> meta-data.
>
> It handles the case where the source mbuf comes from a pool
> with larger data area than the destination pool. The routine
> also has options for skipping data, or truncating at a fixed
> length.
>
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> ---
>   lib/librte_mbuf/rte_mbuf.c           | 74 ++++++++++++++++++++++++++++
>   lib/librte_mbuf/rte_mbuf.h           | 26 ++++++++++
>   lib/librte_mbuf/rte_mbuf_version.map |  1 +
>   3 files changed, 101 insertions(+)
>
> diff --git a/lib/librte_mbuf/rte_mbuf.c b/lib/librte_mbuf/rte_mbuf.c
> index 9a1a1b5f9468..901df0192d2e 100644
> --- a/lib/librte_mbuf/rte_mbuf.c
> +++ b/lib/librte_mbuf/rte_mbuf.c
> @@ -321,6 +321,80 @@ __rte_pktmbuf_linearize(struct rte_mbuf *mbuf)
>   	return 0;
>   }
>   
> +/* Create a deep copy of mbuf */
> +struct rte_mbuf *
> +rte_pktmbuf_copy(const struct rte_mbuf *m, struct rte_mempool *mp,
> +		 uint32_t off, uint32_t len)
> +{
> +	const struct rte_mbuf *seg = m;
> +	struct rte_mbuf *mc, *m_last, **prev;
> +
> +	if (unlikely(off >= m->pkt_len))
> +		return NULL;
> +
> +	mc = rte_pktmbuf_alloc(mp);
> +	if (unlikely(mc == NULL))
> +		return NULL;
> +
> +	if (len > m->pkt_len - off)
> +		len = m->pkt_len - off;
> +
> +	/* clone meta data from original */
> +	mc->port = m->port;
> +	mc->vlan_tci = m->vlan_tci;
> +	mc->vlan_tci_outer = m->vlan_tci_outer;
> +	mc->tx_offload = m->tx_offload;
> +	mc->hash = m->hash;
> +	mc->packet_type = m->packet_type;
> +	mc->timestamp = m->timestamp;

The same is done in rte_pktmbuf_attach(). May be we need a helper
function to copy meta data? Just to avoid duplication in many places.

> +
> +	/* copy private data (if any) */
> +	rte_memcpy(mc + 1, m + 1,
> +		   rte_pktmbuf_priv_size(mp));

priv_size is mempool specific and original mbuf mempool
may have smaller priv_size. I'm not sure that it is safe to copy
outsize of priv_size at least from security point of view.
So, I think it should be RTE_MIN here.

> +
> +	prev = &mc->next;
> +	m_last = mc;
> +	while (len > 0) {
> +		uint32_t copy_len;
> +
> +		while (off >= seg->data_len) {
> +			off -= seg->data_len;
> +			seg = seg->next;
> +		}
> +
> +		/* current buffer is full, chain a new one */
> +		if (rte_pktmbuf_tailroom(m_last) == 0) {
> +			m_last = rte_pktmbuf_alloc(mp);
> +			if (unlikely(m_last == NULL)) {
> +				rte_pktmbuf_free(mc);
> +				return NULL;
> +			}
> +			++mc->nb_segs;
> +			*prev = m_last;
> +			prev = &m_last->next;
> +		}
> +
> +		copy_len = RTE_MIN(seg->data_len - off, len);
> +		if (copy_len > rte_pktmbuf_tailroom(m_last))
> +			copy_len = rte_pktmbuf_tailroom(m_last);
> +
> +		/* append from seg to m_last */
> +		rte_memcpy(rte_pktmbuf_mtod_offset(m_last, char *,
> +						   m_last->data_len),
> +			   rte_pktmbuf_mtod_offset(seg, char *,
> +						   off),
> +			   copy_len);
> +
> +		m_last->data_len += copy_len;
> +		mc->pkt_len += copy_len;
> +		off += copy_len;
> +		len -= copy_len;
> +	}
> +
> +	__rte_mbuf_sanity_check(mc, 1);
> +	return mc;
> +}
> +
>   /* dump a mbuf on console */
>   void
>   rte_pktmbuf_dump(FILE *f, const struct rte_mbuf *m, unsigned dump_len)

[snip]