[ovs-dev] [PATCH v8 05/13] dp-packet: Fix data_len handling multi-seg mbufs.
Eelco Chaudron
echaudro at redhat.com
Mon Jun 18 11:39:30 UTC 2018
On 11 Jun 2018, at 18:21, Tiago Lam wrote:
> When a dp_packet is from a DPDK source, and it contains multi-segment
> mbufs, the data_len is not equal to the packet size, pkt_len. Instead,
> the data_len of each mbuf in the chain should be considered while
> distributing the new (provided) size.
>
> To account for the above dp_packet_set_size() has been changed so
> that,
> in the multi-segment mbufs case, only the data_len on the last mbuf of
> the chain and the total size of the packet, pkt_len, are changed. The
> data_len on the intermediate mbufs preceeding the last mbuf is not
> changed by dp_packet_set_size(). Furthermore, in some cases
> dp_packet_set_size() may be used to set a smaller size than the
> current
> packet size, thus effectively trimming the end of the packet. In the
> multi-segment mbufs case this may lead to lingering mbufs that may
> need
> freeing.
>
> __dp_packet_set_data() now also updates an mbufs' data_len after
> setting
> the data offset. This is so that both fields are always in sync for
> each
> mbuf in a chain.
>
> Co-authored-by: Michael Qiu <qiudayu at chinac.com>
> Co-authored-by: Mark Kavanagh <mark.b.kavanagh at intel.com>
> Co-authored-by: Przemyslaw Lal <przemyslawx.lal at intel.com>
> Co-authored-by: Marcin Ksiadz <mksiadz at gmail.com>
> Co-authored-by: Yuanhan Liu <yliu at fridaylinux.org>
>
> Signed-off-by: Michael Qiu <qiudayu at chinac.com>
> Signed-off-by: Mark Kavanagh <mark.b.kavanagh at intel.com>
> Signed-off-by: Przemyslaw Lal <przemyslawx.lal at intel.com>
> Signed-off-by: Marcin Ksiadz <mksiadz at gmail.com>
> Signed-off-by: Yuanhan Liu <yliu at fridaylinux.org>
> Signed-off-by: Tiago Lam <tiago.lam at intel.com>
> ---
> lib/dp-packet.h | 56
> +++++++++++++++++++++++++++++++++++++++++++++-----------
> 1 file changed, 45 insertions(+), 11 deletions(-)
>
> diff --git a/lib/dp-packet.h b/lib/dp-packet.h
> index 4c104b6..c301ed5 100644
> --- a/lib/dp-packet.h
> +++ b/lib/dp-packet.h
> @@ -429,17 +429,39 @@ dp_packet_size(const struct dp_packet *b)
> static inline void
> dp_packet_set_size(struct dp_packet *b, uint32_t v)
> {
> - /* netdev-dpdk does not currently support segmentation;
> consequently, for
> - * all intents and purposes, 'data_len' (16 bit) and 'pkt_len'
> (32 bit) may
> - * be used interchangably.
> - *
> - * On the datapath, it is expected that the size of packets
> - * (and thus 'v') will always be <= UINT16_MAX; this means that
> there is no
> - * loss of accuracy in assigning 'v' to 'data_len'.
> - */
> - b->mbuf.data_len = (uint16_t)v; /* Current seg length. */
> - b->mbuf.pkt_len = v; /* Total length of all segments
> linked to
> - * this segment. */
> + if (b->source == DPBUF_DPDK) {
This function does not have any check to guarantee that the size set is
valid? i.e. is this not a trim only function? If we increase the size,
no additional mbufs get allocated (see below)
> + struct rte_mbuf *seg = &b->mbuf;
> + struct rte_mbuf *fmbuf = seg;
> + uint16_t pkt_len = v;
> + uint16_t seg_len;
> + uint16_t nb_segs = 0;
> +
> + /* Trim 'v' length bytes from the end of the chained buffers,
> freeing
> + any buffers that may be left floating */
> + while (seg) {
> + seg_len = MIN(pkt_len, seg->data_len);
> + seg->data_len = seg_len;
> +
> + pkt_len -= seg_len;
> + if (pkt_len <= 0) {
> + /* Free the rest of chained mbufs */
> + free_dpdk_buf((struct dp_packet *) seg->next);
> + seg->next = NULL;
> + } else if (!seg->next) {
> + seg->data_len = pkt_len;
Here we could potentially set the size of the segment larger than the
allocated/available buffer.
Also if this is fine, we set it to the wrong value... Assume we have a
single buffer of 100 bytes and we call with v=400. This will result in
data_len being 300, and not 400, should probably be =pkt_len + seg_len
> + }
> +
> + nb_segs += 1;
> + seg = seg->next;
> + }
> +
> + fmbuf->nb_segs = nb_segs;
> + } else {
> + b->mbuf.data_len = v;
> + }
> +
> + /* Total length of all segments linked to this segment. */
> + b->mbuf.pkt_len = v;
> }
>
> static inline uint16_t
> @@ -451,7 +473,19 @@ __packet_data(const struct dp_packet *b)
> static inline void
> __packet_set_data(struct dp_packet *b, uint16_t v)
> {
> + uint16_t prev_ofs = b->mbuf.data_off;
> b->mbuf.data_off = v;
> + int16_t ofs_diff = prev_ofs - b->mbuf.data_off;
> +
> + /* When dealing with DPDK mbufs, keep data_off and data_len in
> sync. Thus,
> + * update data_len if the length changes with the move of
> data_off.
> + * However, if data_len is 0, there's no data to move and
> data_Len should
> + * remain 0. */
> +
> + if (b->mbuf.data_len != 0) {
> + b->mbuf.data_len = MIN(b->mbuf.data_len + ofs_diff,
> + b->mbuf.buf_len - b->mbuf.data_off);
> + }
> }
>
> static inline uint16_t
> --
> 2.7.4
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