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Diffstat (limited to 'src/plugins/af_xdp/device.c')
-rw-r--r--src/plugins/af_xdp/device.c12
1 files changed, 12 insertions, 0 deletions
diff --git a/src/plugins/af_xdp/device.c b/src/plugins/af_xdp/device.c
index fabf85adfa6..35ba617d6e3 100644
--- a/src/plugins/af_xdp/device.c
+++ b/src/plugins/af_xdp/device.c
@@ -208,6 +208,18 @@ af_xdp_create_queue (vlib_main_t * vm, af_xdp_create_if_args_t * args,
umem_config.comp_size = args->txq_size;
umem_config.frame_size =
sizeof (vlib_buffer_t) + vlib_buffer_get_default_data_size (vm);
+ /*
+ * Note about headroom: for some reasons, there seem to be a discrepency
+ * between 0-copy and copy mode:
+ * - 0-copy: XDP_PACKET_HEADROOM will be added to the user headroom
+ * - copy: nothing is added to the user headroom
+ * We privileged 0-copy and set headroom so that frame_headroom +
+ * XDP_PACKET_HEADROOM == sizeof(vlib_buffer_t), ie data will correctly
+ * point to vlib_buffer_t->data for 0-copy. In copy mode, we have to add
+ * XDP_PACKET_HEADROOM to desc offset during refill.
+ */
+ STATIC_ASSERT (sizeof (vlib_buffer_t) >= XDP_PACKET_HEADROOM, "wrong size");
+ umem_config.frame_headroom = sizeof (vlib_buffer_t) - XDP_PACKET_HEADROOM;
umem_config.flags = XDP_UMEM_UNALIGNED_CHUNK_FLAG;
if (xsk_umem__create
(umem, uword_to_pointer (vm->buffer_main->buffer_mem_start, void *),