(Minor changes requested below)

On 07/09/2021 14.35, Lorenzo Bianconi wrote:

quoted

Introduce flags field in xdp_frame and xdp_buffer data structures
to define additional buffer features. At the moment the only
supported buffer feature is multi-buffer bit (mb). Multi-buffer bit
is used to specify if this is a linear buffer (mb = 0) or a multi-buffer
frame (mb = 1). In the latter case the driver is expected to initialize
the skb_shared_info structure at the end of the first buffer to link
together subsequent buffers belonging to the same frame.

Acked-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
---
  include/net/xdp.h | 29 +++++++++++++++++++++++++++++
  1 file changed, 29 insertions(+)

diff --git a/include/net/xdp.h b/include/net/xdp.h
index ad5b02dcb6f4..ed5ea784fd45 100644
--- a/include/net/xdp.h
+++ b/include/net/xdp.h

@@ -66,6 +66,10 @@ struct xdp_txq_info {
  	struct net_device *dev;
  };
+enum xdp_buff_flags {
+	XDP_FLAGS_MULTI_BUFF	= BIT(0), /* non-linear xdp buff */
+};
+
  struct xdp_buff {
  	void *data;
  	void *data_end;

@@ -74,13 +78,30 @@ struct xdp_buff {
  	struct xdp_rxq_info *rxq;
  	struct xdp_txq_info *txq;
  	u32 frame_sz; /* frame size to deduce data_hard_end/reserved tailroom*/
+	u16 flags; /* supported values defined in xdp_flags */

                                                  ^^^^^^^^^
Variable/enum is named "xdp_buff_flags", but comment says "xdp_flags".

ack, I will fix it in v14

I think we should change flags to use u32, because xdp_buff already contain
4 byte padding. (pahole output provided as help below)

ack, I will fix it in v14

quoted

  };
+static __always_inline bool xdp_buff_is_mb(struct xdp_buff *xdp)
+{
+	return !!(xdp->flags & XDP_FLAGS_MULTI_BUFF);
+}
+
+static __always_inline void xdp_buff_set_mb(struct xdp_buff *xdp)
+{
+	xdp->flags |= XDP_FLAGS_MULTI_BUFF;
+}
+
+static __always_inline void xdp_buff_clear_mb(struct xdp_buff *xdp)
+{
+	xdp->flags &= ~XDP_FLAGS_MULTI_BUFF;
+}
+
  static __always_inline void
  xdp_init_buff(struct xdp_buff *xdp, u32 frame_sz, struct xdp_rxq_info *rxq)
  {
  	xdp->frame_sz = frame_sz;
  	xdp->rxq = rxq;
+	xdp->flags = 0;
  }
  static __always_inline void

@@ -122,8 +143,14 @@ struct xdp_frame {
  	 */
  	struct xdp_mem_info mem;
  	struct net_device *dev_rx; /* used by cpumap */
+	u16 flags; /* supported values defined in xdp_flags */

                                                  ^^^^^^^^^
Variable/enum is named "xdp_buff_flags", but comment says "xdp_flags".

Here (for xdp_frame) I also think we should change flags to u32, because
adding this u16 cause extra padding anyhow. (pahole output provided as help
below).

ack, I will fix it in v14

quoted

  };
+static __always_inline bool xdp_frame_is_mb(struct xdp_frame *frame)
+{
+	return !!(frame->flags & XDP_FLAGS_MULTI_BUFF);
+}
+
  #define XDP_BULK_QUEUE_SIZE	16
  struct xdp_frame_bulk {
  	int count;

@@ -180,6 +207,7 @@ void xdp_convert_frame_to_buff(struct xdp_frame *frame, struct xdp_buff *xdp)
  	xdp->data_end = frame->data + frame->len;
  	xdp->data_meta = frame->data - frame->metasize;
  	xdp->frame_sz = frame->frame_sz;
+	xdp->flags = frame->flags;
  }
  static inline

@@ -206,6 +234,7 @@ int xdp_update_frame_from_buff(struct xdp_buff *xdp,
  	xdp_frame->headroom = headroom - sizeof(*xdp_frame);
  	xdp_frame->metasize = metasize;
  	xdp_frame->frame_sz = xdp->frame_sz;
+	xdp_frame->flags = xdp->flags;
  	return 0;
  }

Details below... no need to read any further

Investigating struct xdp_frame with pahole:

$ pahole -C xdp_frame net/core/xdp.o
struct xdp_frame {
	void *                     data;             /*     0     8 */
	u16                        len;              /*     8     2 */
	u16                        headroom;         /*    10     2 */
	u32                        metasize:8;       /*    12: 0  4 */
	u32                        frame_sz:24;      /*    12: 8  4 */
	struct xdp_mem_info        mem;              /*    16     8 */
	struct net_device *        dev_rx;           /*    24     8 */

	/* size: 32, cachelines: 1, members: 7 */
	/* last cacheline: 32 bytes */
};


 pahole -C xdp_frame net/core/xdp.o
struct xdp_frame {
	void *                     data;             /*     0     8 */
	u16                        len;              /*     8     2 */
	u16                        headroom;         /*    10     2 */
	u32                        metasize:8;       /*    12: 0  4 */
	u32                        frame_sz:24;      /*    12: 8  4 */
	struct xdp_mem_info        mem;              /*    16     8 */
	struct net_device *        dev_rx;           /*    24     8 */
	u16                        flags;            /*    32     2 */

	/* size: 40, cachelines: 1, members: 8 */
	/* padding: 6 */
	/* last cacheline: 40 bytes */
};


$ pahole -C xdp_frame net/core/xdp.o
struct xdp_frame {
	void *                     data;             /*     0     8 */
	u16                        len;              /*     8     2 */
	u16                        headroom;         /*    10     2 */
	u32                        metasize:8;       /*    12: 0  4 */
	u32                        frame_sz:24;      /*    12: 8  4 */
	struct xdp_mem_info        mem;              /*    16     8 */
	struct net_device *        dev_rx;           /*    24     8 */
	u32                        flags;            /*    32     4 */

	/* size: 40, cachelines: 1, members: 8 */
	/* padding: 4 */
	/* last cacheline: 40 bytes */
};


Details for struct xdp_buff, it already contains 4 bytes padding.

$ pahole -C xdp_buff net/core/xdp.o
struct xdp_buff {
	void *                     data;             /*     0     8 */
	void *                     data_end;         /*     8     8 */
	void *                     data_meta;        /*    16     8 */
	void *                     data_hard_start;  /*    24     8 */
	struct xdp_rxq_info *      rxq;              /*    32     8 */
	struct xdp_txq_info *      txq;              /*    40     8 */
	u32                        frame_sz;         /*    48     4 */
	u16                        flags;            /*    52     2 */

	/* size: 56, cachelines: 1, members: 8 */
	/* padding: 2 */
	/* last cacheline: 56 bytes */
};

ack, right.

Regards,
Lorenzo