[ovs-dev] [PATCH v5 08/14] dp-packet: Handle multi-seg mbufs in resize__().

Tiago Lam tiago.lam at intel.com
Wed Jul 11 18:23:35 UTC 2018


When enabled with DPDK OvS relies on mbufs allocated by mempools to
receive and output data on DPDK ports. Until now, each OvS dp_packet has
had only one mbuf associated, which is allocated with the maximum
possible size, taking the MTU into account. This approach, however,
doesn't allow us to increase the allocated size in an mbuf, if needed,
since an mbuf is allocated and initialised upon mempool creation. Thus,
in the current implementatin this is dealt with by calling
OVS_NOT_REACHED() and terminating OvS.

To avoid this, and allow the (already) allocated space to be better
used, dp_packet_resize__() now tries to use the available room, both the
tailroom and the headroom, to make enough space for the new data. Since
this happens for packets of source DPBUF_DPDK, the single-segment mbuf
case mentioned above is also covered by this new aproach in resize__().

Signed-off-by: Tiago Lam <tiago.lam at intel.com>
Acked-by: Eelco Chaudron <echaudro at redhat.com>
---
 lib/dp-packet.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 46 insertions(+), 2 deletions(-)

diff --git a/lib/dp-packet.c b/lib/dp-packet.c
index d6e19eb..87af459 100644
--- a/lib/dp-packet.c
+++ b/lib/dp-packet.c
@@ -237,9 +237,51 @@ dp_packet_resize__(struct dp_packet *b, size_t new_headroom, size_t new_tailroom
     new_allocated = new_headroom + dp_packet_size(b) + new_tailroom;
 
     switch (b->source) {
+    /* When resizing mbufs, both a single mbuf and multi-segment mbufs (where
+     * data is not contigously held in memory), both the headroom and the
+     * tailroom available will be used to make more space for where data needs
+     * to be inserted. I.e if there's not enough headroom, data may be shifted
+     * right if there's enough tailroom.
+     * However, this is not bulletproof and in some cases the space available
+     * won't be enough - in those cases, an error should be returned and the
+     * packet dropped. */
     case DPBUF_DPDK:
-        OVS_NOT_REACHED();
+    {
+        size_t miss_len;
+
+        if (new_headroom == dp_packet_headroom(b)) {
+            /* This is a tailroom adjustment. Since there's no tailroom space
+             * left, try and shift data towards the head to free up tail space,
+             * if there's enough headroom */
+
+            miss_len = new_tailroom - dp_packet_tailroom(b);
+
+            if (miss_len <= new_headroom) {
+                dp_packet_shift(b, -miss_len);
+            } else {
+                /* XXX: Handle error case and report error to caller */
+                OVS_NOT_REACHED();
+            }
+        } else {
+            /* Otherwise, this is a headroom adjustment. Try to shift data
+             * towards the tail to free up head space, if there's enough
+             * tailroom */
+
+            miss_len = new_headroom - dp_packet_headroom(b);
 
+
+            if (miss_len <= new_tailroom) {
+                dp_packet_shift(b, miss_len);
+            } else {
+                /* XXX: Handle error case and report error to caller */
+                OVS_NOT_REACHED();
+            }
+        }
+
+        new_base = dp_packet_base(b);
+
+        break;
+    }
     case DPBUF_MALLOC:
         if (new_headroom == dp_packet_headroom(b)) {
             new_base = xrealloc(dp_packet_base(b), new_allocated);
@@ -263,7 +305,9 @@ dp_packet_resize__(struct dp_packet *b, size_t new_headroom, size_t new_tailroom
         OVS_NOT_REACHED();
     }
 
-    dp_packet_set_allocated(b, new_allocated);
+    if (b->source != DPBUF_DPDK) {
+        dp_packet_set_allocated(b, new_allocated);
+    }
     dp_packet_set_base(b, new_base);
 
     new_data = (char *) new_base + new_headroom;
-- 
2.7.4



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