[ovs-dev] [PATCH v16 02/14] dp-packet: Fix data_len handling multi-seg mbufs.
Michal Obrembski
michalx.obrembski at intel.com
Wed Sep 11 13:29:51 UTC 2019
From: Tiago Lam <tiago.lam at intel.com>
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>
Acked-by: Eelco Chaudron <echaudro at redhat.com>
---
lib/dp-packet.h | 101 +++++++++++++++++++++++++++++++++++++++++++++++++-------
1 file changed, 89 insertions(+), 12 deletions(-)
diff --git a/lib/dp-packet.h b/lib/dp-packet.h
index 14f0897..08c4a84 100644
--- a/lib/dp-packet.h
+++ b/lib/dp-packet.h
@@ -474,20 +474,78 @@ dp_packet_size(const struct dp_packet *b)
return b->mbuf.pkt_len;
}
+/* Sets the size of the packet 'b' to 'v'. For non-DPDK packets this only means
+ * setting b->size_, but if used in a DPDK packet it means adjusting the first
+ * mbuf pkt_len and last mbuf data_len, to reflect the real size, which can
+ * lead to free'ing tail mbufs that are no longer used.
+ *
+ * This function should be used for setting the size only, and if there's an
+ * assumption that the tail end of 'b' will be trimmed. For adjusting the head
+ * 'end' of 'b', dp_packet_pull() should be used instead. */
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) {
+ struct rte_mbuf *mbuf = &b->mbuf;
+ uint16_t new_len = v;
+ uint16_t data_len;
+ uint16_t nb_segs = 0;
+ uint16_t pkt_len = 0;
+
+ /* Trim 'v' length bytes from the end of the chained buffers, freeing
+ * any buffers that may be left floating.
+ *
+ * For that traverse over the entire mbuf chain and, for each mbuf,
+ * subtract its 'data_len' from 'new_len' (initially set to 'v'), which
+ * essentially spreads 'new_len' between all existing mbufs in the
+ * chain. While traversing the mbuf chain, we end the traversal if:
+ * - 'new_size' reaches 0, meaning the passed 'v' has been
+ * appropriately spread over the mbuf chain. The remaining mbufs are
+ * freed;
+ * - We reach the last mbuf in the chain, in which case we set the last
+ * mbuf's 'data_len' to the minimum value between the current
+ * 'new_len' (what's leftover from 'v') size and the maximum data the
+ * mbuf can hold (mbuf->buf_len - mbuf->data_off).
+ *
+ * The above formula will thus make sure that when a 'v' is smaller
+ * than the overall 'pkt_len' (sum of all 'data_len'), it sets the new
+ * size and frees the leftover mbufs. In the other hand, if 'v' is
+ * bigger, it sets the size to the maximum available space, but no more
+ * than that. */
+ while (mbuf) {
+ data_len = MIN(new_len, mbuf->data_len);
+ mbuf->data_len = data_len;
+
+ if (new_len - data_len <= 0) {
+ /* Free the rest of chained mbufs */
+ free_dpdk_buf(CONTAINER_OF(mbuf->next, struct dp_packet,
+ mbuf));
+ mbuf->next = NULL;
+ } else if (!mbuf->next) {
+ /* Don't assign more than what we have available */
+ mbuf->data_len = MIN(new_len,
+ mbuf->buf_len - mbuf->data_off);
+ }
+
+ new_len -= data_len;
+ nb_segs += 1;
+ pkt_len += mbuf->data_len;
+ mbuf = mbuf->next;
+ }
+
+ /* pkt_len != v would effectively mean that pkt_len < than 'v' (as
+ * being bigger is logically impossible). Being < than 'v' would mean
+ * the 'v' provided was bigger than the available room, which is the
+ * responsibility of the caller to make sure there is enough room */
+ ovs_assert(pkt_len == v);
+
+ b->mbuf.nb_segs = nb_segs;
+ b->mbuf.pkt_len = pkt_len;
+ } else {
+ b->mbuf.data_len = v;
+ /* Total length of all segments linked to this segment. */
+ b->mbuf.pkt_len = v;
+ }
}
static inline uint16_t
@@ -499,7 +557,26 @@ __packet_data(const struct dp_packet *b)
static inline void
__packet_set_data(struct dp_packet *b, uint16_t v)
{
- b->mbuf.data_off = v;
+ if (b->source == DPBUF_DPDK) {
+ /* Moving data_off away from the first mbuf in the chain is not a
+ * possibility using DPBUF_DPDK dp_packets */
+ ovs_assert(v == UINT16_MAX || v <= b->mbuf.buf_len);
+
+ 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 += ofs_diff;
+ }
+ } else {
+ b->mbuf.data_off = v;
+ }
}
static inline uint16_t
--
2.7.4
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