Introduce a new function, xsk_xdp_adjust_tail, within the XDP program to
adjust the tail of packets. This function utilizes bpf_xdp_adjust_tail to
modify the packet size dynamically based on the 'count' variable.
If the adjustment fails, the packet is dropped using XDP_DROP to ensure
processing of only correctly modified packets.
Signed-off-by: Tushar Vyavahare <tushar.vyavahare@xxxxxxxxx>
---
.../selftests/bpf/progs/xsk_xdp_progs.c | 48 +++++++++++++++++++
tools/testing/selftests/bpf/xsk_xdp_common.h | 1 +
2 files changed, 49 insertions(+)
diff --git a/tools/testing/selftests/bpf/progs/xsk_xdp_progs.c b/tools/testing/selftests/bpf/progs/xsk_xdp_progs.c
index ccde6a4c6319..2e8e2faf17e0 100644
--- a/tools/testing/selftests/bpf/progs/xsk_xdp_progs.c
+++ b/tools/testing/selftests/bpf/progs/xsk_xdp_progs.c
@@ -4,6 +4,8 @@
#include <linux/bpf.h>
#include <bpf/bpf_helpers.h>
#include <linux/if_ether.h>
+#include <linux/ip.h>
+#include <linux/errno.h>
#include "xsk_xdp_common.h"
struct {
@@ -70,4 +72,50 @@ SEC("xdp") int xsk_xdp_shared_umem(struct xdp_md *xdp)
return bpf_redirect_map(&xsk, idx, XDP_DROP);
}
+SEC("xdp.frags") int xsk_xdp_adjust_tail(struct xdp_md *xdp)
+{
+ __u32 buff_len, curr_buff_len;
+ int ret;
+
+ buff_len = bpf_xdp_get_buff_len(xdp);
+ if (buff_len == 0)
+ return XDP_DROP;
+
+ ret = bpf_xdp_adjust_tail(xdp, count);
+ if (ret < 0) {
+ /* Handle unsupported cases */
+ if (ret == -EOPNOTSUPP) {
+ /* Set count to -EOPNOTSUPP to indicate to userspace that this case is
+ * unsupported
+ */
+ count = -EOPNOTSUPP;
+ return bpf_redirect_map(&xsk, 0, XDP_DROP);
+ }
+
+ return XDP_DROP;
+ }
+
+ curr_buff_len = bpf_xdp_get_buff_len(xdp);
+ if (curr_buff_len != buff_len + count)
+ return XDP_DROP;
+
+ if (curr_buff_len > buff_len) {
+ __u32 *pkt_data = (void *)(long)xdp->data;
+ __u32 len, words_to_end, seq_num;
+
+ len = curr_buff_len - PKT_HDR_ALIGN;
+ words_to_end = len / sizeof(*pkt_data) - 1;
+ seq_num = words_to_end;
+
+ /* Convert sequence number to network byte order. Store this in the last 4 bytes of
+ * the packet. Use 'count' to determine the position at the end of the packet for
+ * storing the sequence number.
+ */
+ seq_num = __constant_htonl(words_to_end);
+ bpf_xdp_store_bytes(xdp, curr_buff_len - count, &seq_num, sizeof(seq_num));
+ }
+
+ return bpf_redirect_map(&xsk, 0, XDP_DROP);
+}
+
char _license[] SEC("license") = "GPL";
diff --git a/tools/testing/selftests/bpf/xsk_xdp_common.h b/tools/testing/selftests/bpf/xsk_xdp_common.h
index 5a6f36f07383..45810ff552da 100644
--- a/tools/testing/selftests/bpf/xsk_xdp_common.h
+++ b/tools/testing/selftests/bpf/xsk_xdp_common.h
@@ -4,6 +4,7 @@
#define XSK_XDP_COMMON_H_
#define MAX_SOCKETS 2
+#define PKT_HDR_ALIGN (sizeof(struct ethhdr) + 2) /* Just to align the data in the packet */
struct xdp_info {
__u64 count;
--
2.34.1
