[v11,bpf-next,18/18] bpf: add bpf_xdp_adjust_data selftest

diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_adjust_data.c b/tools/testing/selftests/bpf/prog_tests/xdp_adjust_data.c
new file mode 100644
index 000000000000..a3e098b72fc9
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/xdp_adjust_data.c
@@ -0,0 +1,55 @@ 
+// SPDX-License-Identifier: GPL-2.0
+#include <test_progs.h>
+#include <network_helpers.h>
+
+void test_xdp_update_frag(void)
+{
+	const char *file = "./test_xdp_update_frags.o";
+	__u32 duration, retval, size;
+	struct bpf_object *obj;
+	int err, prog_fd;
+	__u8 *buf;
+
+	err = bpf_prog_load(file, BPF_PROG_TYPE_XDP, &obj, &prog_fd);
+	if (CHECK_FAIL(err))
+		return;
+
+	buf = malloc(128);
+	if (CHECK(!buf, "malloc()", "error:%s\n", strerror(errno)))
+		return;
+
+	memset(buf, 0, 128);
+
+	err = bpf_prog_test_run(prog_fd, 1, buf, 128,
+				buf, &size, &retval, &duration);
+	free(buf);
+
+	CHECK(err || retval != XDP_DROP,
+	      "128b", "err %d errno %d retval %d size %d\n",
+	      err, errno, retval, size);
+
+	buf = malloc(9000);
+	if (CHECK(!buf, "malloc()", "error:%s\n", strerror(errno)))
+		return;
+
+	memset(buf, 0, 9000);
+	buf[5000] = 0xaa; /* marker at offset 5000 (frag0) */
+
+	err = bpf_prog_test_run(prog_fd, 1, buf, 9000,
+				buf, &size, &retval, &duration);
+
+	/* test_xdp_update_frags: buf[5000]: 0xaa -> 0xbb */
+	CHECK(err || retval != XDP_PASS || buf[5000] != 0xbb,
+	      "9000b", "err %d errno %d retval %d size %d\n",
+	      err, errno, retval, size);
+
+	free(buf);
+
+	bpf_object__close(obj);
+}
+
+void test_xdp_adjust_data(void)
+{
+	if (test__start_subtest("xdp_adjust_data"))
+		test_xdp_update_frag();
+}
diff --git a/tools/testing/selftests/bpf/progs/test_xdp_update_frags.c b/tools/testing/selftests/bpf/progs/test_xdp_update_frags.c
new file mode 100644
index 000000000000..c2d5772007f3
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_xdp_update_frags.c
@@ -0,0 +1,41 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public
+ * License as published by the Free Software Foundation.
+ */
+#include <linux/bpf.h>
+#include <linux/if_ether.h>
+#include <bpf/bpf_helpers.h>
+
+int _version SEC("version") = 1;
+
+SEC("xdp_adjust_frags")
+int _xdp_adjust_frags(struct xdp_md *xdp)
+{
+	__u8 *data_end = (void *)(long)xdp->data_end;
+	__u8 *data = (void *)(long)xdp->data;
+	__u32 offset = 5000; /* marker offset */
+	int base_offset, ret = XDP_DROP;
+
+	base_offset = bpf_xdp_adjust_data(xdp, offset);
+	if (base_offset < 0 || base_offset > offset)
+		return XDP_DROP;
+
+	data_end = (void *)(long)xdp->data_end;
+	data = (void *)(long)xdp->data;
+
+	if (data + 1 > data_end)
+		goto out;
+
+	if (*data != 0xaa) /* marker */
+		goto out;
+
+	*data = 0xbb; /* update the marker */
+	ret = XDP_PASS;
+out:
+	bpf_xdp_adjust_data(xdp, 0);
+	return ret;
+}
+
+char _license[] SEC("license") = "GPL";