[PATCH RFC net-next 3/5] selftests: drv-net: Test XDP head adjustment with bpf_dynptr

[Nimrod Oren]

Update xdp_adjst_head_shrnk_data to use bpf_dynptr_slice to read the
data right after the headers, instead of bpf_xdp_load_bytes.

This may avoid a copy by returning a direct pointer to the dynptr data.

Also, use bpf_dynptr_read and bpf_dynptr_write to move the headers,
instead of bpf_xdp_load_bytes and bpf_xdp_store_bytes.

Signed-off-by: Nimrod Oren <no...@nvidia.com>
Reviewed-by: Carolina Jubran <cjub...@nvidia.com>
Reviewed-by: Dragos Tatulea <dtatu...@nvidia.com>
---
 .../selftests/net/lib/xdp_native.bpf.c        | 35 +++++++------------
 1 file changed, 12 insertions(+), 23 deletions(-)

diff --git a/tools/testing/selftests/net/lib/xdp_native.bpf.c 
b/tools/testing/selftests/net/lib/xdp_native.bpf.c
index ff768fbc8606..71172d32c529 100644
--- a/tools/testing/selftests/net/lib/xdp_native.bpf.c
+++ b/tools/testing/selftests/net/lib/xdp_native.bpf.c
@@ -398,10 +398,11 @@ static int xdp_adjst_tail(struct xdp_md *ctx, __u16 port)
 static int xdp_adjst_head_shrnk_data(struct xdp_md *ctx, __u64 hdr_len,
                                     __u32 offset)
 {
-       char tmp_buff[MAX_ADJST_OFFSET];
+       char tmp_buff[MAX_ADJST_OFFSET] = {0};
+       struct bpf_dynptr ptr;
        struct udphdr *udph;
-       void *offset_ptr;
        __u32 udp_csum = 0;
+       void *data = NULL;
 
        /* Update the length information in the IP and UDP headers before
         * adjusting the headroom. This simplifies accessing the relevant
@@ -414,37 +415,25 @@ static int xdp_adjst_head_shrnk_data(struct xdp_md *ctx, 
__u64 hdr_len,
        if (!udph)
                return -1;
 
-       offset = (offset & 0x1ff) >= MAX_ADJST_OFFSET ? MAX_ADJST_OFFSET :
-                                    offset & 0xff;
-       if (offset == 0)
-               return -1;
-
-       if (bpf_xdp_load_bytes(ctx, hdr_len, tmp_buff, offset) < 0)
+       bpf_dynptr_from_xdp(ctx, 0, &ptr);
+       data = bpf_dynptr_slice(&ptr, hdr_len, tmp_buff, sizeof(tmp_buff));
+       if (!data)
                return -1;
 
-       udp_csum = bpf_csum_diff((__be32 *)tmp_buff, offset, 0, 0, udp_csum);
+       udp_csum = bpf_csum_diff(data, offset, 0, 0, udp_csum);
 
        udph->check = (__u16)csum_fold_helper(udp_csum);
 
-       if (bpf_xdp_load_bytes(ctx, 0, tmp_buff, MAX_ADJST_OFFSET) < 0)
-               return -1;
-
-       if (bpf_xdp_adjust_head(ctx, offset) < 0)
-               return -1;
-
-       if (offset > MAX_ADJST_OFFSET)
-               return -1;
-
-       if (hdr_len > MAX_ADJST_OFFSET || hdr_len == 0)
-               return -1;
-
        /* Added here to handle clang complain about negative value */
        hdr_len = hdr_len & 0xff;
 
-       if (hdr_len == 0)
+       if (bpf_dynptr_read(tmp_buff, hdr_len, &ptr, 0, 0) < 0)
                return -1;
 
-       if (bpf_xdp_store_bytes(ctx, 0, tmp_buff, hdr_len) < 0)
+       if (bpf_dynptr_write(&ptr, offset, tmp_buff, hdr_len, 0) < 0)
+               return -1;
+
+       if (bpf_xdp_adjust_head(ctx, offset) < 0)
                return -1;
 
        return 0;
-- 
2.45.0