Re: [PATCH bpf v8 5/5] selftests/bpf: add strparser test for bpf

Thanks for expanding tests.

On Tue, Jan 21, 2025 at 01:07 PM +08, Jiayuan Chen wrote:

Add test cases for bpf + strparser and separated them from sockmap_basic, as strparser has more encapsulation and parsing capabilities compared to sockmap.

Signed-off-by: Jiayuan Chen mrpre@163.com

.../selftests/bpf/prog_tests/sockmap_basic.c | 53 -- .../selftests/bpf/prog_tests/sockmap_strp.c | 452 ++++++++++++++++++ .../selftests/bpf/progs/test_sockmap_strp.c | 53 ++ 3 files changed, 505 insertions(+), 53 deletions(-) create mode 100644 tools/testing/selftests/bpf/prog_tests/sockmap_strp.c create mode 100644 tools/testing/selftests/bpf/progs/test_sockmap_strp.c

diff --git a/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c b/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c index 0c51b7288978..f8953455db29 100644 --- a/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c +++ b/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c @@ -531,57 +531,6 @@ static void test_sockmap_skb_verdict_shutdown(void) test_sockmap_pass_prog__destroy(skel); } -static void test_sockmap_stream_pass(void) -{

• int zero = 0, sent, recvd;
• int verdict, parser;
• int err, map;
• int c = -1, p = -1;
• struct test_sockmap_pass_prog *pass = NULL;
• char snd[256] = "0123456789";
• char rcv[256] = "0";
• pass = test_sockmap_pass_prog__open_and_load();
• verdict = bpf_program__fd(pass->progs.prog_skb_verdict);
• parser = bpf_program__fd(pass->progs.prog_skb_parser);
• map = bpf_map__fd(pass->maps.sock_map_rx);
• err = bpf_prog_attach(parser, map, BPF_SK_SKB_STREAM_PARSER, 0);
• if (!ASSERT_OK(err, "bpf_prog_attach stream parser"))

• goto out;
  

• err = bpf_prog_attach(verdict, map, BPF_SK_SKB_STREAM_VERDICT, 0);
• if (!ASSERT_OK(err, "bpf_prog_attach stream verdict"))

• goto out;
  

• err = create_pair(AF_INET, SOCK_STREAM, &c, &p);
• if (err)

• goto out;
  

• /* sk_data_ready of 'p' will be replaced by strparser handler */
• err = bpf_map_update_elem(map, &zero, &p, BPF_NOEXIST);
• if (!ASSERT_OK(err, "bpf_map_update_elem(p)"))

• goto out_close;
  

• /*

• * as 'prog_skb_parser' return the original skb len and
  

• * 'prog_skb_verdict' return SK_PASS, the kernel will just
  

• * pass it through to original socket 'p'
  

• */
  

• sent = xsend(c, snd, sizeof(snd), 0);
• ASSERT_EQ(sent, sizeof(snd), "xsend(c)");
• recvd = recv_timeout(p, rcv, sizeof(rcv), SOCK_NONBLOCK,

• 	     IO_TIMEOUT_SEC);
  

• ASSERT_EQ(recvd, sizeof(rcv), "recv_timeout(p)");

-out_close:

• close(c);
• close(p);

-out:

• test_sockmap_pass_prog__destroy(pass);

-} static void test_sockmap_skb_verdict_fionread(bool pass_prog) { @@ -1101,8 +1050,6 @@ void test_sockmap_basic(void) test_sockmap_progs_query(BPF_SK_SKB_VERDICT); if (test__start_subtest("sockmap skb_verdict shutdown")) test_sockmap_skb_verdict_shutdown();

• if (test__start_subtest("sockmap stream parser and verdict pass"))

• test_sockmap_stream_pass();
  

  if (test__start_subtest("sockmap skb_verdict fionread")) test_sockmap_skb_verdict_fionread(true); if (test__start_subtest("sockmap skb_verdict fionread on drop"))

diff --git a/tools/testing/selftests/bpf/prog_tests/sockmap_strp.c b/tools/testing/selftests/bpf/prog_tests/sockmap_strp.c new file mode 100644 index 000000000000..01ed1fca1d9c --- /dev/null +++ b/tools/testing/selftests/bpf/prog_tests/sockmap_strp.c @@ -0,0 +1,452 @@ +// SPDX-License-Identifier: GPL-2.0 +#include <error.h> +#include <netinet/tcp.h> +#include <test_progs.h> +#include "sockmap_helpers.h" +#include "test_skmsg_load_helpers.skel.h" +#include "test_sockmap_strp.skel.h"

Nit: add new line to separate cpp defines visually

+#define STRP_PKT_HEAD_LEN 4 +#define STRP_PKT_BODY_LEN 6 +#define STRP_PKT_FULL_LEN (STRP_PKT_HEAD_LEN + STRP_PKT_BODY_LEN)

Nit: add new line to constants visually

+static const char packet[STRP_PKT_FULL_LEN] = "head+body\0"; +static const int test_packet_num = 100;

+/* current implementation of tcp_bpf_recvmsg_parser() invoke

Nit: grammar, "invoke*s*"

• • data_ready with sk held if skb exist in sk_receive_queue.

Nit: grammar, "exist*s*"

• • Then for data_ready implementation of strparser, it will
• • delay the read operation if sk was held and EAGAIN is returned.
• */

+static int sockmap_strp_consume_pre_data(int p) +{

• int recvd;
• bool retried = false;
• char rcv[10];

+retry:

• errno = 0;
• recvd = recv_timeout(p, rcv, sizeof(rcv), 0, 1);
• if (recvd < 0 && errno == EAGAIN && retried == false) {

• /* On the first call, EAGAIN will certainly be returned.
  

•  * Waiting 1 second is pretty enough wait workqueue finish.
  

Nit: style, "Wait for workqueue to finish."

•  */
  

• sleep(1);
  

• retried = true;
  

• goto retry;
  

• }
• if (!ASSERT_EQ(recvd, STRP_PKT_FULL_LEN, "recv_timeout(pre-data)") ||

Meaningful error message like "recv error or truncated data" would be better. ASSERT_EQ / CHECK macros print the function name, so "(pre-data)" tag is redundant.

•    !ASSERT_OK(memcmp(packet, rcv, STRP_PKT_FULL_LEN),
  

• 		"memcmp pre-data"))
  

Suggested error message: "data mismatch".

• return -1;
  

• return 0;

+}

+static struct test_sockmap_strp *sockmap_strp_init(int *out_map, bool pass,

• 				   bool need_parser)
  

+{

• struct test_sockmap_strp *strp = NULL;
• int verdict, parser;
• int err;
• strp = test_sockmap_strp__open_and_load();
• *out_map = bpf_map__fd(strp->maps.sock_map);
• if (need_parser)

• parser = bpf_program__fd(strp->progs.prog_skb_parser_partial);
  

• else

• parser = bpf_program__fd(strp->progs.prog_skb_parser);
  

• if (pass)

• verdict = bpf_program__fd(strp->progs.prog_skb_verdict_pass);
  

• else

• verdict = bpf_program__fd(strp->progs.prog_skb_verdict);
  

• err = bpf_prog_attach(parser, *out_map, BPF_SK_SKB_STREAM_PARSER, 0);
• if (!ASSERT_OK(err, "bpf_prog_attach stream parser"))

• goto err;
  

• err = bpf_prog_attach(verdict, *out_map, BPF_SK_SKB_STREAM_VERDICT, 0);
• if (!ASSERT_OK(err, "bpf_prog_attach stream verdict"))

• goto err;
  

• return strp;

+err:

• test_sockmap_strp__destroy(strp);
• return NULL;

+}

+/* Dispatch packets to different socket by packet size:

• •                  ------  ------
    

• •                 | pkt4 || pkt1 |... > remote socket
    

• • ------ ------ / ------ ------
• • | pkt8 | pkt7 |...
• • ------ ------ \ ------ ------

• •                 | pkt3 || pkt2 |... > local socket
    

• •                  ------  ------
    

• */

+static void test_sockmap_strp_dispatch_pkt(int family, int sotype) +{

• int i, j, zero = 0, one = 1, recvd;
• int err, map;
• int c0 = -1, p0 = -1, c1 = -1, p1 = -1;
• struct test_sockmap_strp *strp = NULL;
• int test_cnt = 6;
• char rcv[10];
• struct {

• char	data[7];
  

• int	data_len;
  

• int	send_cnt;
  

• int	*receiver;
  

• } send_dir[2] = {

• /* data expected to deliver to local */
  

• {"llllll", 6, 0, &p0},
  

• /* data expected to deliver to remote */
  

• {"rrrrr",  5, 0, &c1}
  

• };
• strp = sockmap_strp_init(&map, false, false);
• if (!ASSERT_TRUE(strp, "sockmap_strp_init"))

• return;
  

• err = create_socket_pairs(family, sotype, &c0, &c1, &p0, &p1);
• if (!ASSERT_OK(err, "create_socket_pairs()"))

• goto out;
  

• err = bpf_map_update_elem(map, &zero, &p0, BPF_NOEXIST);
• if (!ASSERT_OK(err, "bpf_map_update_elem(p0)"))

• goto out_close;
  

• err = bpf_map_update_elem(map, &one, &p1, BPF_NOEXIST);
• if (!ASSERT_OK(err, "bpf_map_update_elem(p1)"))

• goto out_close;
  

• err = setsockopt(c1, IPPROTO_TCP, TCP_NODELAY, &zero, sizeof(zero));
• if (!ASSERT_OK(err, "setsockopt(TCP_NODELAY)"))

• goto out_close;
  

• /* deliver data with data size greater than 5 to local */
• strp->data->verdict_max_size = 5;
• for (i = 0; i < test_cnt; i++) {

• int d = i % 2;
  

• xsend(c0, send_dir[d].data, send_dir[d].data_len, 0);
  

• send_dir[d].send_cnt++;
  

• }
• for (i = 0; i < 2; i++) {

• for (j = 0; j < send_dir[i].send_cnt; j++) {
  

• 	int expected = send_dir[i].data_len;
  

• 	recvd = recv_timeout(*send_dir[i].receiver, rcv,
  

• 			     expected, MSG_DONTWAIT,
  

• 			     IO_TIMEOUT_SEC);
  

• 	if (!ASSERT_EQ(recvd, expected, "recv_timeout()"))
  

• 		goto out_close;
  

• 	if (!ASSERT_OK(memcmp(send_dir[i].data, rcv, recvd),
  

• 		       "memcmp(rcv)"))
  

• 		goto out_close;
  

• }
  

• }

+out_close:

• close(c0);
• close(c1);
• close(p0);
• close(p1);

+out:

• test_sockmap_strp__destroy(strp);

+}

+/* We have multiple packets in one skb

• • ---

• • | packet1 | packet2 | ...

• • ---

• */

+static void test_sockmap_strp_multiple_pkt(int family, int sotype) +{

• int i, zero = 0;
• int sent, recvd, total;
• int err, map;
• int c = -1, p = -1;
• struct test_sockmap_strp *strp = NULL;
• char *snd = NULL, *rcv = NULL;
• strp = sockmap_strp_init(&map, true, true);
• if (!ASSERT_TRUE(strp, "sockmap_strp_init"))

• return;
  

• err = create_pair(family, sotype, &c, &p);
• if (err)

• goto out;
  

• err = bpf_map_update_elem(map, &zero, &p, BPF_NOEXIST);
• if (!ASSERT_OK(err, "bpf_map_update_elem(zero, p)"))

• goto out_close;
  

• /* construct multiple packets in one buffer */
• total = test_packet_num * STRP_PKT_FULL_LEN;
• snd = malloc(total);
• rcv = malloc(total + 1);
• if (!ASSERT_TRUE(snd, "malloc(snd)") ||

•    !ASSERT_TRUE(rcv, "malloc(rcv)"))
  

• goto out_close;
  

• for (i = 0; i < test_packet_num; i++) {

• memcpy(snd + i * STRP_PKT_FULL_LEN,
  

•        packet, STRP_PKT_FULL_LEN);
  

• }
• sent = xsend(c, snd, total, 0);
• if (!ASSERT_EQ(sent, total, "xsend(c)"))

• goto out_close;
  

• /* try to recv one more byte to avoid truncation check */
• recvd = recv_timeout(p, rcv, total + 1, MSG_DONTWAIT, IO_TIMEOUT_SEC);
• if (!ASSERT_EQ(recvd, total, "recv(rcv)"))

• goto out_close;
  

• /* we sent TCP segment with multiple encapsulation

• * then check whether packets are handled correctly
  

• */
  

• if (!ASSERT_OK(memcmp(snd, rcv, total), "memcmp(snd, rcv)"))

• goto out_close;
  

+out_close:

• close(c);
• close(p);
• if (snd)

• free(snd);
  

• if (rcv)

• free(rcv);
  

+out:

• test_sockmap_strp__destroy(strp);

+}

+/* Test strparser with partial read */ +static void test_sockmap_strp_partial_read(int family, int sotype) +{

• int zero = 0, recvd, off;
• int err, map;
• int c = -1, p = -1;
• struct test_sockmap_strp *strp = NULL;
• char rcv[STRP_PKT_FULL_LEN + 1] = "0";
• strp = sockmap_strp_init(&map, true, true);
• if (!ASSERT_TRUE(strp, "sockmap_strp_init"))

• return;
  

• err = create_pair(family, sotype, &c, &p);
• if (err)

• goto out;
  

• /* sk_data_ready of 'p' will be replaced by strparser handler */
• err = bpf_map_update_elem(map, &zero, &p, BPF_NOEXIST);
• if (!ASSERT_OK(err, "bpf_map_update_elem(zero, p)"))

• goto out_close;
  

• /* 1.1 send partial head, 1 byte header left*/

Nit: missing space before comment-close tag, "left */".

• off = STRP_PKT_HEAD_LEN - 1;
• xsend(c, packet, off, 0);
• recvd = recv_timeout(p, rcv, sizeof(rcv), MSG_DONTWAIT, 1);
• if (!ASSERT_EQ(-1, recvd, "insufficient head, should no data recvd"))

"partial head sent, expected no data"

• goto out_close;
  

• /* 1.2 send remaining head and body */
• xsend(c, packet + off, STRP_PKT_FULL_LEN - off, 0);
• recvd = recv_timeout(p, rcv, sizeof(rcv), MSG_DONTWAIT, IO_TIMEOUT_SEC);
• if (!ASSERT_EQ(recvd, STRP_PKT_FULL_LEN, "should full data recvd"))

"expected full data"

• goto out_close;
  

• /* 2.1 send partial head, 1 byte header left */
• off = STRP_PKT_HEAD_LEN - 1;
• xsend(c, packet, off, 0);
• /* 2.2 send remaining head and partial body, 1 byte body left */
• xsend(c, packet + off, STRP_PKT_FULL_LEN - off - 1, 0);
• off = STRP_PKT_FULL_LEN - 1;
• recvd = recv_timeout(p, rcv, sizeof(rcv), MSG_DONTWAIT, 1);
• if (!ASSERT_EQ(-1, recvd, "insufficient body, should no data read"))

"partial body sent, expected no data"

• goto out_close;
  

• /* 2.3 send remaining body */
• xsend(c, packet + off, STRP_PKT_FULL_LEN - off, 0);
• recvd = recv_timeout(p, rcv, sizeof(rcv), MSG_DONTWAIT, IO_TIMEOUT_SEC);
• if (!ASSERT_EQ(recvd, STRP_PKT_FULL_LEN, "should full data recvd"))

"expected full data"

• goto out_close;
  

+out_close:

• close(c);
• close(p);

+out:

• test_sockmap_strp__destroy(strp);

+}

+/* Test simple socket read/write with strparser + FIONREAD */ +static void test_sockmap_strp_pass(int family, int sotype, bool fionread) +{

• int zero = 0, pkt_size = STRP_PKT_FULL_LEN, sent, recvd, avail;
• int err, map;
• int c = -1, p = -1;
• int test_cnt = 10, i;
• struct test_sockmap_strp *strp = NULL;
• char rcv[STRP_PKT_FULL_LEN + 1] = "0";
• strp = sockmap_strp_init(&map, true, true);
• if (!ASSERT_TRUE(strp, "sockmap_strp_init"))

• return;
  

• err = create_pair(family, sotype, &c, &p);
• if (err)

• goto out;
  

• /* inject some data before bpf process, it should be read

• * correctly because we check sk_receive_queue in
  

• * tcp_bpf_recvmsg_parser()
  

• */
  

• sent = xsend(c, packet, pkt_size, 0);
• if (!ASSERT_EQ(sent, pkt_size, "xsend(pre-data)"))

• goto out_close;
  

• /* sk_data_ready of 'p' will be replaced by strparser handler */
• err = bpf_map_update_elem(map, &zero, &p, BPF_NOEXIST);
• if (!ASSERT_OK(err, "bpf_map_update_elem(p)"))

• goto out_close;
  

• /* consume previous data we injected */
• if (sockmap_strp_consume_pre_data(p))

• goto out_close;
  

• /* Previously, we encountered issues such as deadlocks and

• * sequence errors that resulted in the inability to read
  

• * continuously. Therefore, we perform multiple iterations
  

• * of testing here.
  

• */
  

• for (i = 0; i < test_cnt; i++) {

• sent = xsend(c, packet, pkt_size, 0);
  

• if (!ASSERT_EQ(sent, pkt_size, "xsend(c)"))
  

• 	goto out_close;
  

• recvd = recv_timeout(p, rcv, sizeof(rcv), MSG_DONTWAIT,
  

• 		     IO_TIMEOUT_SEC);
  

• if (!ASSERT_EQ(recvd, pkt_size, "recv_timeout(p)") ||
  

•     !ASSERT_OK(memcmp(packet, rcv, pkt_size),
  

• 		  "memcmp"))
  

• 	goto out_close;
  

• }
• if (fionread) {

• sent = xsend(c, packet, pkt_size, 0);
  

• if (!ASSERT_EQ(sent, pkt_size, "second xsend(c)"))
  

• 	goto out_close;
  

• err = ioctl(p, FIONREAD, &avail);
  

• if (!ASSERT_OK(err, "ioctl(FIONREAD) error") ||
  

•     !ASSERT_EQ(avail, pkt_size, "ioctl(FIONREAD)"))
  

• 	goto out_close;
  

• recvd = recv_timeout(p, rcv, sizeof(rcv), MSG_DONTWAIT,
  

• 		     IO_TIMEOUT_SEC);
  

• if (!ASSERT_EQ(recvd, pkt_size, "second recv_timeout(p)") ||
  

•     !ASSERT_OK(memcmp(packet, rcv, pkt_size),
  

• 	      "second memcmp"))
  

• 	goto out_close;
  

• }

+out_close:

• close(c);
• close(p);

+out:

• test_sockmap_strp__destroy(strp);

+}

+/* Test strparser with verdict mode */ +static void test_sockmap_strp_verdict(int family, int sotype) +{

• int zero = 0, one = 1, sent, recvd, off;
• int err, map;
• int c0 = -1, p0 = -1, c1 = -1, p1 = -1;
• struct test_sockmap_strp *strp = NULL;
• char rcv[STRP_PKT_FULL_LEN + 1] = "0";
• strp = sockmap_strp_init(&map, false, true);
• if (!ASSERT_TRUE(strp, "sockmap_strp_init"))

• return;
  

• /* We simulate a reverse proxy server.

• * When p0 receives data from c0, we forward it to c1.
  

• * From c1's perspective, it will consider this data
  

• * as being sent by p1.
  

• */
  

• err = create_socket_pairs(family, sotype, &c0, &c1, &p0, &p1);
• if (!ASSERT_OK(err, "create_socket_pairs()"))

• goto out;
  

• err = bpf_map_update_elem(map, &zero, &p0, BPF_NOEXIST);
• if (!ASSERT_OK(err, "bpf_map_update_elem(p0)"))

• goto out_close;
  

• err = bpf_map_update_elem(map, &one, &p1, BPF_NOEXIST);
• if (!ASSERT_OK(err, "bpf_map_update_elem(c1)"))

• goto out_close;
  

• sent = xsend(c0, packet, STRP_PKT_FULL_LEN, 0);
• if (!ASSERT_EQ(sent, STRP_PKT_FULL_LEN, "xsend(c0)"))

• goto out_close;
  

• recvd = recv_timeout(c1, rcv, sizeof(rcv), MSG_DONTWAIT,

• 	     IO_TIMEOUT_SEC);
  

• if (!ASSERT_EQ(recvd, STRP_PKT_FULL_LEN, "recv_timeout(p1)") ||

•    !ASSERT_OK(memcmp(packet, rcv, STRP_PKT_FULL_LEN),
  

• 	  "received data does not match the sent data"))
  

• goto out_close;
  

• /* send again to ensure the stream is functioning correctly. */
• sent = xsend(c0, packet, STRP_PKT_FULL_LEN, 0);
• if (!ASSERT_EQ(sent, STRP_PKT_FULL_LEN, "second xsend(c0)"))

• goto out_close;
  

• /* partial read */
• off = STRP_PKT_FULL_LEN / 2;
• recvd = recv_timeout(c1, rcv, off, MSG_DONTWAIT,

• 	     IO_TIMEOUT_SEC);
  

• recvd += recv_timeout(c1, rcv + off, sizeof(rcv) - off, MSG_DONTWAIT,

• 	      IO_TIMEOUT_SEC);
  

• if (!ASSERT_EQ(recvd, STRP_PKT_FULL_LEN, "partial recv_timeout(c1)") ||

•    !ASSERT_OK(memcmp(packet, rcv, STRP_PKT_FULL_LEN),
  

• 	  "partial received data does not match the sent data"))
  

• goto out_close;
  

+out_close:

• close(c0);
• close(c1);
• close(p0);
• close(p1);

+out:

• test_sockmap_strp__destroy(strp);

+}

+void test_sockmap_strp(void) +{

• if (test__start_subtest("sockmap strp tcp pass"))

• test_sockmap_strp_pass(AF_INET, SOCK_STREAM, false);
  

• if (test__start_subtest("sockmap strp tcp v6 pass"))

• test_sockmap_strp_pass(AF_INET6, SOCK_STREAM, false);
  

• if (test__start_subtest("sockmap strp tcp pass fionread"))

• test_sockmap_strp_pass(AF_INET, SOCK_STREAM, true);
  

• if (test__start_subtest("sockmap strp tcp v6 pass fionread"))

• test_sockmap_strp_pass(AF_INET6, SOCK_STREAM, true);
  

• if (test__start_subtest("sockmap strp tcp verdict"))

• test_sockmap_strp_verdict(AF_INET, SOCK_STREAM);
  

• if (test__start_subtest("sockmap strp tcp v6 verdict"))

• test_sockmap_strp_verdict(AF_INET6, SOCK_STREAM);
  

• if (test__start_subtest("sockmap strp tcp partial read"))

• test_sockmap_strp_partial_read(AF_INET, SOCK_STREAM);
  

• if (test__start_subtest("sockmap strp tcp multiple packets"))

• test_sockmap_strp_multiple_pkt(AF_INET, SOCK_STREAM);
  

• if (test__start_subtest("sockmap strp tcp dispatch"))

• test_sockmap_strp_dispatch_pkt(AF_INET, SOCK_STREAM);
  

+} diff --git a/tools/testing/selftests/bpf/progs/test_sockmap_strp.c b/tools/testing/selftests/bpf/progs/test_sockmap_strp.c new file mode 100644 index 000000000000..dde3d5bec515 --- /dev/null +++ b/tools/testing/selftests/bpf/progs/test_sockmap_strp.c @@ -0,0 +1,53 @@ +// SPDX-License-Identifier: GPL-2.0 +#include <linux/bpf.h> +#include <bpf/bpf_helpers.h> +#include <bpf/bpf_endian.h> +int verdict_max_size = 10000; +struct {

• __uint(type, BPF_MAP_TYPE_SOCKMAP);
• __uint(max_entries, 20);
• __type(key, int);
• __type(value, int);

+} sock_map SEC(".maps");

+SEC("sk_skb/stream_verdict") +int prog_skb_verdict(struct __sk_buff *skb) +{

• __u32 one = 1;
• if (skb->len > verdict_max_size)

• return SK_PASS;
  

• return bpf_sk_redirect_map(skb, &sock_map, one, 0);

+}

+SEC("sk_skb/stream_verdict") +int prog_skb_verdict_pass(struct __sk_buff *skb) +{

• return SK_PASS;

+}

+SEC("sk_skb/stream_parser") +int prog_skb_parser(struct __sk_buff *skb) +{

• return skb->len;

+}

+SEC("sk_skb/stream_parser") +int prog_skb_parser_partial(struct __sk_buff *skb) +{

• /* agreement with the test program on a 4-byte size header

• * and 6-byte body.
  

• */
  

• if (skb->len < 4) {

• /* need more header to determine full length */
  

• return 0;
  

• }
• /* return full length decoded from header.

• * the return value may be larger than skb->len which
  

• * means framework must wait body coming.
  

• */
  

• return 10;

+}

+char _license[] SEC("license") = "GPL";