[[RFC xdp-hints] 13/16] libbpf: Helpers to access XDP frame metadata

[Ederson de Souza <ederson.desouza@intel.com>]

Two new pairs of helpers: `xsk_umem__adjust_prod_data` and
`xsk_umem__adjust_prod_data_meta` for data that is being produced by the
application - such as data that will be sent; and
`xsk_umem__adjust_cons_data` and `xsk_umem__adjust_cons_data_meta`,
for data being consumed - such as data obtained from the completion
queue.

Those function should usually be used on data obtained via
`xsk_umem__get_data`. Didn't change this function to avoid API breaks.

Signed-off-by: Ederson de Souza <ederson.desouza@intel.com>
---
 tools/lib/bpf/libbpf.map |  4 ++++
 tools/lib/bpf/xsk.c      | 26 ++++++++++++++++++++++++++
 tools/lib/bpf/xsk.h      |  7 +++++++
 3 files changed, 37 insertions(+)

diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 492db50a4cd7..663585f7f186 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -375,4 +375,8 @@ LIBBPF_0.5.0 {
 		bpf_map_lookup_and_delete_elem_flags;
 		bpf_object__gen_loader;
 		libbpf_set_strict_mode;
+		xsk_umem__adjust_cons_data;
+		xsk_umem__adjust_cons_data_meta;
+		xsk_umem__adjust_prod_data;
+		xsk_umem__adjust_prod_data_meta;
 } LIBBPF_0.4.0;
diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
index e9b619aa0cdf..17e8045eac0e 100644
--- a/tools/lib/bpf/xsk.c
+++ b/tools/lib/bpf/xsk.c
@@ -119,6 +119,30 @@ int xsk_socket__fd(const struct xsk_socket *xsk)
 	return xsk ? xsk->fd : -EINVAL;
 }
 
+void *xsk_umem__adjust_prod_data(void *umem_data, const struct xsk_umem *umem)
+{
+	return umem_data + umem->config.frame_headroom + umem->config.xdp_headroom;
+}
+
+void *xsk_umem__adjust_prod_data_meta(void *umem_data, const struct xsk_umem *umem)
+{
+	if (!umem->config.xdp_headroom)
+		return NULL;
+	return umem_data;
+}
+
+void *xsk_umem__adjust_cons_data(void *umem_data, const struct xsk_umem *umem)
+{
+	return umem_data;
+}
+
+void *xsk_umem__adjust_cons_data_meta(void *umem_data, const struct xsk_umem *umem)
+{
+	if (!umem->config.xdp_headroom)
+		return NULL;
+	return umem_data;
+}
+
 static bool xsk_page_aligned(void *buffer)
 {
 	unsigned long addr = (unsigned long)buffer;
@@ -135,6 +159,7 @@ static void xsk_set_umem_config(struct xsk_umem_config *cfg,
 		cfg->frame_size = XSK_UMEM__DEFAULT_FRAME_SIZE;
 		cfg->frame_headroom = XSK_UMEM__DEFAULT_FRAME_HEADROOM;
 		cfg->flags = XSK_UMEM__DEFAULT_FLAGS;
+		cfg->xdp_headroom = XSK_UMEM__DEFAULT_XDP_HEADROOM;
 		return;
 	}
 
@@ -143,6 +168,7 @@ static void xsk_set_umem_config(struct xsk_umem_config *cfg,
 	cfg->frame_size = usr_cfg->frame_size;
 	cfg->frame_headroom = usr_cfg->frame_headroom;
 	cfg->flags = usr_cfg->flags;
+	cfg->xdp_headroom = usr_cfg->xdp_headroom;
 }
 
 static int xsk_set_xdp_socket_config(struct xsk_socket_config *cfg,
diff --git a/tools/lib/bpf/xsk.h b/tools/lib/bpf/xsk.h
index 01c12dca9c10..7f4143150746 100644
--- a/tools/lib/bpf/xsk.h
+++ b/tools/lib/bpf/xsk.h
@@ -248,12 +248,18 @@ static inline __u64 xsk_umem__add_offset_to_addr(__u64 addr)
 LIBBPF_API int xsk_umem__fd(const struct xsk_umem *umem);
 LIBBPF_API int xsk_socket__fd(const struct xsk_socket *xsk);
 
+LIBBPF_API void *xsk_umem__adjust_prod_data(void *umem_data, const struct xsk_umem *umem);
+LIBBPF_API void *xsk_umem__adjust_prod_data_meta(void *umem_data, const struct xsk_umem *umem);
+LIBBPF_API void *xsk_umem__adjust_cons_data(void *umem_data, const struct xsk_umem *umem);
+LIBBPF_API void *xsk_umem__adjust_cons_data_meta(void *umem_data, const struct xsk_umem *umem);
+
 #define XSK_RING_CONS__DEFAULT_NUM_DESCS      2048
 #define XSK_RING_PROD__DEFAULT_NUM_DESCS      2048
 #define XSK_UMEM__DEFAULT_FRAME_SHIFT    12 /* 4096 bytes */
 #define XSK_UMEM__DEFAULT_FRAME_SIZE     (1 << XSK_UMEM__DEFAULT_FRAME_SHIFT)
 #define XSK_UMEM__DEFAULT_FRAME_HEADROOM 0
 #define XSK_UMEM__DEFAULT_FLAGS 0
+#define XSK_UMEM__DEFAULT_XDP_HEADROOM 0
 
 struct xsk_umem_config {
 	__u32 fill_size;
@@ -261,6 +267,7 @@ struct xsk_umem_config {
 	__u32 frame_size;
 	__u32 frame_headroom;
 	__u32 flags;
+	__u32 xdp_headroom;
 };
 
 LIBBPF_API int xsk_setup_xdp_prog(int ifindex,
-- 
2.32.0