samples/bpf: fixup some tools to be able to support xdp multibuffer

Bugzilla: https://bugzilla.redhat.com/2137876

commit 772251742262bd651529a3cea3ee756b71e95a29
Author: Andy Gospodarek <andrew.gospodarek@broadcom.com>
Date:   Tue Jun 21 17:54:02 2022 +0000

    samples/bpf: fixup some tools to be able to support xdp multibuffer
    
    This changes the section name for the bpf program embedded in these
    files to "xdp.frags" to allow the programs to be loaded on drivers that
    are using an MTU greater than PAGE_SIZE.  Rather than directly accessing
    the buffers, the packet data is now accessed via xdp helper functions to
    provide an example for those who may need to write more complex
    programs.
    
    v2: remove new unnecessary variable
    
    Signed-off-by: Andy Gospodarek <gospo@broadcom.com>
    Acked-by: John Fastabend <john.fastabend@gmail.com>
    Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
    Link: https://lore.kernel.org/r/20220621175402.35327-1-gospo@broadcom.com
    Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Signed-off-by: Felix Maurer <fmaurer@redhat.com>

samples/bpf/xdp1_kern.c

@@ -39,11 +39,13 @@ static int parse_ipv6(void *data, u64 nh_off, void *data_end)
 	return ip6h->nexthdr;
 }
 
-SEC("xdp1")
+#define XDPBUFSIZE	64
+SEC("xdp.frags")
 int xdp_prog1(struct xdp_md *ctx)
 {
-	void *data_end = (void *)(long)ctx->data_end;
-	void *data = (void *)(long)ctx->data;
+	__u8 pkt[XDPBUFSIZE] = {};
+	void *data_end = &pkt[XDPBUFSIZE-1];
+	void *data = pkt;
 	struct ethhdr *eth = data;
 	int rc = XDP_DROP;
 	long *value;
@@ -51,6 +53,9 @@ int xdp_prog1(struct xdp_md *ctx)
 	u64 nh_off;
 	u32 ipproto;
 
+	if (bpf_xdp_load_bytes(ctx, 0, pkt, sizeof(pkt)))
+		return rc;
+
 	nh_off = sizeof(*eth);
 	if (data + nh_off > data_end)
 		return rc;

samples/bpf/xdp2_kern.c

@@ -55,11 +55,13 @@ static int parse_ipv6(void *data, u64 nh_off, void *data_end)
 	return ip6h->nexthdr;
 }
 
-SEC("xdp1")
+#define XDPBUFSIZE	64
+SEC("xdp.frags")
 int xdp_prog1(struct xdp_md *ctx)
 {
-	void *data_end = (void *)(long)ctx->data_end;
-	void *data = (void *)(long)ctx->data;
+	__u8 pkt[XDPBUFSIZE] = {};
+	void *data_end = &pkt[XDPBUFSIZE-1];
+	void *data = pkt;
 	struct ethhdr *eth = data;
 	int rc = XDP_DROP;
 	long *value;
@@ -67,6 +69,9 @@ int xdp_prog1(struct xdp_md *ctx)
 	u64 nh_off;
 	u32 ipproto;
 
+	if (bpf_xdp_load_bytes(ctx, 0, pkt, sizeof(pkt)))
+		return rc;
+
 	nh_off = sizeof(*eth);
 	if (data + nh_off > data_end)
 		return rc;

samples/bpf/xdp_tx_iptunnel_kern.c

@@ -212,7 +212,7 @@ static __always_inline int handle_ipv6(struct xdp_md *xdp)
 	return XDP_TX;
 }
 
-SEC("xdp_tx_iptunnel")
+SEC("xdp.frags")
 int _xdp_tx_iptunnel(struct xdp_md *xdp)
 {
 	void *data_end = (void *)(long)xdp->data_end;