xsk: remove explicit ring structure from uapi

In this commit we remove the explicit ring structure from the the
uapi. It is tricky for an uapi to depend on a certain L1 cache line
size, since it can differ for variants of the same architecture. Now,
we let the user application determine the offsets of the producer,
consumer and descriptors by asking the socket via getsockopt.

A typical flow would be (Rx ring):

  struct xdp_mmap_offsets off;
  struct xdp_desc *ring;
  u32 *prod, *cons;
  void *map;
  ...

  getsockopt(fd, SOL_XDP, XDP_MMAP_OFFSETS, &off, &optlen);

  map = mmap(NULL, off.rx.desc +
		   NUM_DESCS * sizeof(struct xdp_desc),
		   PROT_READ | PROT_WRITE,
		   MAP_SHARED | MAP_POPULATE, sfd,
		   XDP_PGOFF_RX_RING);
  prod = map + off.rx.producer;
  cons = map + off.rx.consumer;
  ring = map + off.rx.desc;

Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

2 files changed, 46 insertions, 0 deletions

diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index 2970735..378dd92 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -489,6 +489,35 @@ static int xsk_getsockopt(struct socket *sock, int level, int optname,
 
 		return 0;
 	}
+	case XDP_MMAP_OFFSETS:
+	{
+		struct xdp_mmap_offsets off;
+
+		if (len < sizeof(off))
+			return -EINVAL;
+
+		off.rx.producer = offsetof(struct xdp_rxtx_ring, ptrs.producer);
+		off.rx.consumer = offsetof(struct xdp_rxtx_ring, ptrs.consumer);
+		off.rx.desc	= offsetof(struct xdp_rxtx_ring, desc);
+		off.tx.producer = offsetof(struct xdp_rxtx_ring, ptrs.producer);
+		off.tx.consumer = offsetof(struct xdp_rxtx_ring, ptrs.consumer);
+		off.tx.desc	= offsetof(struct xdp_rxtx_ring, desc);
+
+		off.fr.producer = offsetof(struct xdp_umem_ring, ptrs.producer);
+		off.fr.consumer = offsetof(struct xdp_umem_ring, ptrs.consumer);
+		off.fr.desc	= offsetof(struct xdp_umem_ring, desc);
+		off.cr.producer = offsetof(struct xdp_umem_ring, ptrs.producer);
+		off.cr.consumer = offsetof(struct xdp_umem_ring, ptrs.consumer);
+		off.cr.desc	= offsetof(struct xdp_umem_ring, desc);
+
+		len = sizeof(off);
+		if (copy_to_user(optval, &off, len))
+			return -EFAULT;
+		if (put_user(len, optlen))
+			return -EFAULT;
+
+		return 0;
+	}
 	default:
 		break;
 	}
diff --git a/net/xdp/xsk_queue.h b/net/xdp/xsk_queue.h
index 62e43be..cb8e5be 100644
--- a/net/xdp/xsk_queue.h
+++ b/net/xdp/xsk_queue.h
@@ -13,6 +13,23 @@
 
 #define RX_BATCH_SIZE 16
 
+struct xdp_ring {
+	u32 producer ____cacheline_aligned_in_smp;
+	u32 consumer ____cacheline_aligned_in_smp;
+};
+
+/* Used for the RX and TX queues for packets */
+struct xdp_rxtx_ring {
+	struct xdp_ring ptrs;
+	struct xdp_desc desc[0] ____cacheline_aligned_in_smp;
+};
+
+/* Used for the fill and completion queues for buffers */
+struct xdp_umem_ring {
+	struct xdp_ring ptrs;
+	u32 desc[0] ____cacheline_aligned_in_smp;
+};
+
 struct xsk_queue {
 	struct xdp_umem_props umem_props;
 	u32 ring_mask;