selftests/xsk: transmit and receive multi-buffer packets

Add the ability to send and receive packets that are larger than the
size of a umem frame, using the AF_XDP /XDP multi-buffer
support. There are three pieces of code that need to be changed to
achieve this: the Rx path, the Tx path, and the validation logic.

Both the Rx path and Tx could only deal with a single fragment per
packet. The Tx path is extended with a new function called
pkt_nb_frags() that can be used to retrieve the number of fragments a
packet will consume. We then create these many fragments in a loop and
fill the N-1 first ones to the max size limit to use the buffer space
efficiently, and the Nth one with whatever data that is left. This
goes on until we have filled in at the most BATCH_SIZE worth of
descriptors and fragments. If we detect that the next packet would
lead to BATCH_SIZE number of fragments sent being exceeded, we do not
send this packet and finish the batch. This packet is instead sent in
the next iteration of BATCH_SIZE fragments.

For Rx, we loop over all fragments we receive as usual, but for every
descriptor that we receive we call a new validation function called
is_frag_valid() to validate the consistency of this fragment. The code
then checks if the packet continues in the next frame. If so, it loops
over the next packet and performs the same validation. once we have
received the last fragment of the packet we also call the function
is_pkt_valid() to validate the packet as a whole. If we get to the end
of the batch and we are not at the end of the current packet, we back
out the partial packet and end the loop. Once we get into the receive
loop next time, we start over from the beginning of that packet. This
so the code becomes simpler at the cost of some performance.

The validation function is_frag_valid() checks that the sequence and
packet numbers are correct at the start and end of each fragment.

Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Link: https://lore.kernel.org/r/20230719132421.584801-19-maciej.fijalkowski@intel.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/tools/testing/selftests/bpf/xskxceiver.h b/tools/testing/selftests/bpf/xskxceiver.h
index aaf27e067640..310b48ad8a3a 100644
--- a/tools/testing/selftests/bpf/xskxceiver.h
+++ b/tools/testing/selftests/bpf/xskxceiver.h
@@ -38,6 +38,7 @@
 #define MAX_TEARDOWN_ITER 10
 #define PKT_HDR_SIZE (sizeof(struct ethhdr) + 2) /* Just to align the data in the packet */
 #define MIN_PKT_SIZE 64
+#define MAX_ETH_JUMBO_SIZE 9000
 #define USLEEP_MAX 10000
 #define SOCK_RECONF_CTR 10
 #define BATCH_SIZE 64
@@ -47,7 +48,7 @@
 #define DEFAULT_UMEM_BUFFERS (DEFAULT_PKT_CNT / 4)
 #define RX_FULL_RXQSIZE 32
 #define UMEM_HEADROOM_TEST_SIZE 128
-#define XSK_UMEM__INVALID_FRAME_SIZE (XSK_UMEM__DEFAULT_FRAME_SIZE + 1)
+#define XSK_UMEM__INVALID_FRAME_SIZE (MAX_ETH_JUMBO_SIZE + 1)
 #define HUGEPAGE_SIZE (2 * 1024 * 1024)
 #define PKT_DUMP_NB_TO_PRINT 16