xsk: add sock_diag interface for AF_XDP

This patch adds the sock_diag interface for querying sockets from user
space. Tools like iproute2 ss(8) can use this interface to list open
AF_XDP sockets.

The user-space ABI is defined in linux/xdp_diag.h and includes netlink
request and response structs. The request can query sockets and the
response contains socket information about the rings, umems, inode and
more.

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

include/uapi/linux/xdp_diag.h

@@ -0,0 +1,72 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ * xdp_diag: interface for query/monitor XDP sockets
+ * Copyright(c) 2019 Intel Corporation.
+ */
+
+#ifndef _LINUX_XDP_DIAG_H
+#define _LINUX_XDP_DIAG_H
+
+#include <linux/types.h>
+
+struct xdp_diag_req {
+	__u8	sdiag_family;
+	__u8	sdiag_protocol;
+	__u16	pad;
+	__u32	xdiag_ino;
+	__u32	xdiag_show;
+	__u32	xdiag_cookie[2];
+};
+
+struct xdp_diag_msg {
+	__u8	xdiag_family;
+	__u8	xdiag_type;
+	__u16	pad;
+	__u32	xdiag_ino;
+	__u32	xdiag_cookie[2];
+};
+
+#define XDP_SHOW_INFO		(1 << 0) /* Basic information */
+#define XDP_SHOW_RING_CFG	(1 << 1)
+#define XDP_SHOW_UMEM		(1 << 2)
+#define XDP_SHOW_MEMINFO	(1 << 3)
+
+enum {
+	XDP_DIAG_NONE,
+	XDP_DIAG_INFO,
+	XDP_DIAG_UID,
+	XDP_DIAG_RX_RING,
+	XDP_DIAG_TX_RING,
+	XDP_DIAG_UMEM,
+	XDP_DIAG_UMEM_FILL_RING,
+	XDP_DIAG_UMEM_COMPLETION_RING,
+	XDP_DIAG_MEMINFO,
+	__XDP_DIAG_MAX,
+};
+
+#define XDP_DIAG_MAX (__XDP_DIAG_MAX - 1)
+
+struct xdp_diag_info {
+	__u32	ifindex;
+	__u32	queue_id;
+};
+
+struct xdp_diag_ring {
+	__u32	entries; /*num descs */
+};
+
+#define XDP_DU_F_ZEROCOPY (1 << 0)
+
+struct xdp_diag_umem {
+	__u64	size;
+	__u32	id;
+	__u32	num_pages;
+	__u32	chunk_size;
+	__u32	headroom;
+	__u32	ifindex;
+	__u32	queue_id;
+	__u32	flags;
+	__u32	refs;
+};
+
+#endif /* _LINUX_XDP_DIAG_H */