[ovs-dev,v5,05/14] dp-packet: Fix data_len handling multi-seg mbufs.

Message ID 1531333421-235225-6-git-send-email-tiago.lam@intel.com
State New
Headers show
Series
  • Support multi-segment mbufs
Related show

Commit Message

Lam, Tiago July 11, 2018, 6:23 p.m.
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@chinac.com>
Co-authored-by: Mark Kavanagh <mark.b.kavanagh@intel.com>
Co-authored-by: Przemyslaw Lal <przemyslawx.lal@intel.com>
Co-authored-by: Marcin Ksiadz <mksiadz@gmail.com>
Co-authored-by: Yuanhan Liu <yliu@fridaylinux.org>

Signed-off-by: Michael Qiu <qiudayu@chinac.com>
Signed-off-by: Mark Kavanagh <mark.b.kavanagh@intel.com>
Signed-off-by: Przemyslaw Lal <przemyslawx.lal@intel.com>
Signed-off-by: Marcin Ksiadz <mksiadz@gmail.com>
Signed-off-by: Yuanhan Liu <yliu@fridaylinux.org>
Signed-off-by: Tiago Lam <tiago.lam@intel.com>
Acked-by: Eelco Chaudron <echaudro@redhat.com>
---
 lib/dp-packet.h | 76 ++++++++++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 64 insertions(+), 12 deletions(-)

Patch

diff --git a/lib/dp-packet.h b/lib/dp-packet.h
index 6376039..d2803af 100644
--- a/lib/dp-packet.h
+++ b/lib/dp-packet.h
@@ -429,17 +429,49 @@  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) {
+        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 */
+        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
@@ -451,7 +483,27 @@  __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 = MIN(b->mbuf.data_len + ofs_diff,
+                                   b->mbuf.buf_len - b->mbuf.data_off);
+        }
+    } else {
+        b->mbuf.data_off = v;
+    }
 }
 
 static inline uint16_t