Make it possible for the application to determine whether the AF_XDP
socket is running in zero-copy mode. To achieve this, add a new
getsockopt option XDP_OPTIONS that returns flags. The only flag
supported for now is the zero-copy mode indicator.

Signed-off-by: Maxim Mikityanskiy <redacted>
Reviewed-by: Tariq Toukan <redacted>
Acked-by: Saeed Mahameed <redacted>
---
 include/uapi/linux/if_xdp.h       |  7 +++++++
 net/xdp/xsk.c                     | 22 ++++++++++++++++++++++
 tools/include/uapi/linux/if_xdp.h |  7 +++++++
 3 files changed, 36 insertions(+)

diff --git a/include/uapi/linux/if_xdp.h b/include/uapi/linux/if_xdp.h
index caed8b1614ff..9ae4b4e08b68 100644
--- a/include/uapi/linux/if_xdp.h
+++ b/include/uapi/linux/if_xdp.h

@@ -46,6 +46,7 @@ struct xdp_mmap_offsets {
 #define XDP_UMEM_FILL_RING             5
 #define XDP_UMEM_COMPLETION_RING       6
 #define XDP_STATISTICS                 7
+#define XDP_OPTIONS                    8

 struct xdp_umem_reg {
        __u64 addr; /* Start of packet data area */

@@ -60,6 +61,12 @@ struct xdp_statistics {
        __u64 tx_invalid_descs; /* Dropped due to invalid descriptor */
 };

+struct xdp_options {
+       __u32 flags;
+};
+
+#define XDP_OPTIONS_FLAG_ZEROCOPY (1 << 0)

+
 /* Pgoff for mmaping the rings */
 #define XDP_PGOFF_RX_RING                        0
 #define XDP_PGOFF_TX_RING               0x80000000

diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index b68a380f50b3..998199109d5c 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c

@@ -650,6 +650,28 @@ static int xsk_getsockopt(struct socket *sock, int level, int optname,

                return 0;
        }
+       case XDP_OPTIONS:
+       {
+               struct xdp_options opts;
+
+               if (len < sizeof(opts))
+                       return -EINVAL;
+
+               opts.flags = 0;

+
+               mutex_lock(&xs->mutex);
+               if (xs->zc)
+                       opts.flags |= XDP_OPTIONS_FLAG_ZEROCOPY;
+               mutex_unlock(&xs->mutex);
+
+               len = sizeof(opts);
+               if (copy_to_user(optval, &opts, len))
+                       return -EFAULT;
+               if (put_user(len, optlen))
+                       return -EFAULT;
+
+               return 0;
+       }
        default:
                break;
        }

diff --git a/tools/include/uapi/linux/if_xdp.h b/tools/include/uapi/linux/if_xdp.h
index caed8b1614ff..9ae4b4e08b68 100644
--- a/tools/include/uapi/linux/if_xdp.h
+++ b/tools/include/uapi/linux/if_xdp.h

@@ -46,6 +46,7 @@ struct xdp_mmap_offsets {
 #define XDP_UMEM_FILL_RING             5
 #define XDP_UMEM_COMPLETION_RING       6
 #define XDP_STATISTICS                 7
+#define XDP_OPTIONS                    8

 struct xdp_umem_reg {
        __u64 addr; /* Start of packet data area */

@@ -60,6 +61,12 @@ struct xdp_statistics {
        __u64 tx_invalid_descs; /* Dropped due to invalid descriptor */
 };

+struct xdp_options {
+       __u32 flags;
+};
+
+#define XDP_OPTIONS_FLAG_ZEROCOPY (1 << 0)
+
 /* Pgoff for mmaping the rings */
 #define XDP_PGOFF_RX_RING                        0
 #define XDP_PGOFF_TX_RING               0x80000000
--

2.19.1