Install a BPF filter on packetIO socket

This filters out Tx packets send from other programs on the SDKLT Rx side.
Previously, these Tx packets ended up in the SDKLT receive process (incl. callbacks)
as if they came from the switch.

Author: pudelkoM

src/linux/bcmlu/bcmpkt/unet/bcmlu_tpacket.c

@@ -103,6 +103,7 @@
 #include <errno.h>
 #include <unistd.h>
 #include <poll.h>
+#include <linux/filter.h>
 #include <linux/if.h>
 #include <linux/if_packet.h>
 #include <linux/if_ether.h>
@@ -601,6 +602,41 @@ bcmlu_tpacket_netif_bind(int sock_fd, bcmlu_tpacket_t *tp)
     SHR_FUNC_EXIT();
 }
 
+static int
+bcmlu_tpacket_socket_install_filter(int sock_fd, bcmlu_tpacket_t *tp)
+{
+    // Set Berkeley Packet Filter (BPF) for the socket. The filters here are
+    // copied directly from Stratum. No need to change anything here.
+    const struct sock_filter filters[] = {
+        // 0. Retrieve "packet type" (see <netpacket/packet.h> for types) from
+        //    linux-specific magical negative offset
+        {0x28, 0, 0, 0xfffff004},
+        // 1. Branch if equal to 4 (PACKET_OUTGOING). Go to 2 if so, 3 otherwise.
+        {0x15, 0, 1, 0x00000004},
+        // 2. Return 0 (ignore packet)
+        {0x6, 0, 0, 0x00000000},
+        // 3. Return 65535 (capture entire packet)
+        {0x6, 0, 0, 0x0000ffff},
+    };
+    const struct sock_fprog fprog = {
+        sizeof(filters) / sizeof(filters[0]),
+        (struct sock_filter*) filters,
+    };
+
+    SHR_FUNC_ENTER(BSL_UNIT_UNKNOWN);
+    SHR_NULL_CHECK(tp, SHR_E_PARAM);
+
+    if (setsockopt(sock_fd, SOL_SOCKET, SO_ATTACH_FILTER, &fprog,
+                   sizeof(fprog)) < 0) {
+        SHR_IF_ERR_MSG_EXIT
+            (SHR_E_FAIL,
+             (BSL_META_U(tp->unit, "setsockopt SO_ATTACH_FILTER error\n")));
+    }
+
+exit:
+    SHR_FUNC_EXIT();
+}
+
 static int
 bcmlu_tpacket_socket_create(bcmlu_tpacket_t *tp)
 {
@@ -647,6 +683,10 @@ bcmlu_tpacket_socket_create(bcmlu_tpacket_t *tp)
                 (BSL_META_U(tp->unit, "Open netif %s\n"), tp->netif.name));
 #endif
 
+    /*! Install BPF filter. */
+    SHR_IF_ERR_EXIT
+        (bcmlu_tpacket_socket_install_filter(sock_fd, tp));
+
     /*! Bind socket to the netif. */
     SHR_IF_ERR_EXIT
         (bcmlu_tpacket_netif_bind(sock_fd, tp));
@@ -1043,6 +1083,7 @@ bcmlu_tpacket_packet_handle(bcmlu_tpacket_t *tp,
         data[17] == (rhdr->ethertype & 0xFF)) {
         if (data[18] != (rhdr->signature >> 8) ||
             data[19] != (rhdr->signature & 0xFF) ||
+//            data[20] != BCMPKT_RCPU_OP_TX ||
             data[20] != BCMPKT_RCPU_OP_RX ||
             data[21] != BCMPKT_RCPU_F_MODHDR) {
             ring->rcpu_hdr_err++;