netdev - [PATCH bpf-next 01/21] xsk: prepare 'options' in xdp

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Date: Thu, 18 May 2023 20:05:25 +0200
From: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
To: bpf@...r.kernel.org,
	ast@...nel.org,
	daniel@...earbox.net,
	andrii@...nel.org
Cc: netdev@...r.kernel.org,
	magnus.karlsson@...el.com,
	tirthendu.sarkar@...el.com,
	maciej.fijalkowski@...el.com,
	bjorn@...nel.org
Subject: [PATCH bpf-next 01/21] xsk: prepare 'options' in xdp_desc for multi-buffer use

From: Tirthendu Sarkar <tirthendu.sarkar@...el.com>

Use the 'options' field in xdp_desc as a packet continuity marker. Since
'options' field was unused till now and was expected to be set to 0, the
'eop' descriptor will have it set to 0, while the non-eop descriptors
will have to set it to 1. This ensures legacy applications continue to
work without needing any change for single-buffer packets.

Add helper functions and extend xskq_prod_reserve_desc() to use the
'options' field.

Signed-off-by: Tirthendu Sarkar <tirthendu.sarkar@...el.com>
---
 include/uapi/linux/if_xdp.h | 16 ++++++++++++++++
 net/xdp/xsk.c               |  8 ++++----
 net/xdp/xsk_queue.h         | 12 +++++++++---
 3 files changed, 29 insertions(+), 7 deletions(-)

diff --git a/include/uapi/linux/if_xdp.h b/include/uapi/linux/if_xdp.h
index a78a8096f4ce..4acc3a9430f3 100644
--- a/include/uapi/linux/if_xdp.h
+++ b/include/uapi/linux/if_xdp.h
@@ -108,4 +108,20 @@ struct xdp_desc {
 
 /* UMEM descriptor is __u64 */
 
+/* Flag indicating that the packet continues with the buffer pointed out by the
+ * next frame in the ring. The end of the packet is signalled by setting this
+ * bit to zero. For single buffer packets, every descriptor has 'options' set
+ * to 0 and this maintains backward compatibility.
+ */
+#define XDP_PKT_CONTD (1 << 0)
+
+/* Maximum number of descriptors supported as frags for a packet. So the total
+ * number of descriptors supported for a packet is XSK_DESC_MAX_FRAGS + 1. The
+ * max frags supported by skb is 16 for page sizes greater than 4K and 17 or
+ * more for 4K or lesser page sizes. XSK_DESC_MAX_FRAGS is set as the minimum
+ * value of 16 so that xsk applications see the same behavior for all
+ * architectures.
+ */
+#define XSK_DESC_MAX_FRAGS 16
+
 #endif /* _LINUX_IF_XDP_H */
diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index cc1e7f15fa73..99f90a0d04ae 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -135,14 +135,14 @@ int xsk_reg_pool_at_qid(struct net_device *dev, struct xsk_buff_pool *pool,
 	return 0;
 }
 
-static int __xsk_rcv_zc(struct xdp_sock *xs, struct xdp_buff *xdp, u32 len)
+static int __xsk_rcv_zc(struct xdp_sock *xs, struct xdp_buff *xdp, u32 len, u32 flags)
 {
 	struct xdp_buff_xsk *xskb = container_of(xdp, struct xdp_buff_xsk, xdp);
 	u64 addr;
 	int err;
 
 	addr = xp_get_handle(xskb);
-	err = xskq_prod_reserve_desc(xs->rx, addr, len);
+	err = xskq_prod_reserve_desc(xs->rx, addr, len, flags);
 	if (err) {
 		xs->rx_queue_full++;
 		return err;
@@ -189,7 +189,7 @@ static int __xsk_rcv(struct xdp_sock *xs, struct xdp_buff *xdp)
 	}
 
 	xsk_copy_xdp(xsk_xdp, xdp, len);
-	err = __xsk_rcv_zc(xs, xsk_xdp, len);
+	err = __xsk_rcv_zc(xs, xsk_xdp, len, 0);
 	if (err) {
 		xsk_buff_free(xsk_xdp);
 		return err;
@@ -259,7 +259,7 @@ static int xsk_rcv(struct xdp_sock *xs, struct xdp_buff *xdp)
 
 	if (xdp->rxq->mem.type == MEM_TYPE_XSK_BUFF_POOL) {
 		len = xdp->data_end - xdp->data;
-		return __xsk_rcv_zc(xs, xdp, len);
+		return __xsk_rcv_zc(xs, xdp, len, 0);
 	}
 
 	err = __xsk_rcv(xs, xdp);
diff --git a/net/xdp/xsk_queue.h b/net/xdp/xsk_queue.h
index 6d40a77fccbe..ad81b19e6fdf 100644
--- a/net/xdp/xsk_queue.h
+++ b/net/xdp/xsk_queue.h
@@ -130,6 +130,11 @@ static inline bool xskq_cons_read_addr_unchecked(struct xsk_queue *q, u64 *addr)
 	return false;
 }
 
+static inline bool xp_unused_options_set(u16 options)
+{
+	return options & ~XDP_PKT_CONTD;
+}
+
 static inline bool xp_aligned_validate_desc(struct xsk_buff_pool *pool,
 					    struct xdp_desc *desc)
 {
@@ -141,7 +146,7 @@ static inline bool xp_aligned_validate_desc(struct xsk_buff_pool *pool,
 	if (desc->addr >= pool->addrs_cnt)
 		return false;
 
-	if (desc->options)
+	if (xp_unused_options_set(desc->options))
 		return false;
 	return true;
 }
@@ -158,7 +163,7 @@ static inline bool xp_unaligned_validate_desc(struct xsk_buff_pool *pool,
 	    xp_desc_crosses_non_contig_pg(pool, addr, desc->len))
 		return false;
 
-	if (desc->options)
+	if (xp_unused_options_set(desc->options))
 		return false;
 	return true;
 }
@@ -360,7 +365,7 @@ static inline void xskq_prod_write_addr_batch(struct xsk_queue *q, struct xdp_de
 }
 
 static inline int xskq_prod_reserve_desc(struct xsk_queue *q,
-					 u64 addr, u32 len)
+					 u64 addr, u32 len, u32 flags)
 {
 	struct xdp_rxtx_ring *ring = (struct xdp_rxtx_ring *)q->ring;
 	u32 idx;
@@ -372,6 +377,7 @@ static inline int xskq_prod_reserve_desc(struct xsk_queue *q,
 	idx = q->cached_prod++ & q->ring_mask;
 	ring->desc[idx].addr = addr;
 	ring->desc[idx].len = len;
+	ring->desc[idx].options = flags;
 
 	return 0;
 }
-- 
2.34.1