[RFC bpf-next v2 03/11] xsk: Support XDP_TX_METADATA_LEN

[Stanislav Fomichev <sdf@google.com>]

For zerocopy mode, tx_desc->addr can point to the arbitrary offset
and carry some TX metadata in the headroom. For copy mode, there
is no way currently to populate skb metadata.

Introduce new XDP_TX_METADATA_LEN that indicates how many bytes
to treat as metadata. Metadata bytes come prior to tx_desc address
(same as in RX case).

Signed-off-by: Stanislav Fomichev <sdf@google.com>
---
 include/net/xdp_sock.h      |  1 +
 include/net/xsk_buff_pool.h |  1 +
 include/uapi/linux/if_xdp.h |  1 +
 net/xdp/xsk.c               | 31 ++++++++++++++++++++++++++++++-
 net/xdp/xsk_buff_pool.c     |  1 +
 net/xdp/xsk_queue.h         |  7 ++++---
 6 files changed, 38 insertions(+), 4 deletions(-)

diff --git a/include/net/xdp_sock.h b/include/net/xdp_sock.h
index e96a1151ec75..30018b3b862d 100644
--- a/include/net/xdp_sock.h
+++ b/include/net/xdp_sock.h
@@ -51,6 +51,7 @@ struct xdp_sock {
 	struct list_head flush_node;
 	struct xsk_buff_pool *pool;
 	u16 queue_id;
+	u8 tx_metadata_len;
 	bool zc;
 	enum {
 		XSK_READY = 0,
diff --git a/include/net/xsk_buff_pool.h b/include/net/xsk_buff_pool.h
index a8d7b8a3688a..751fea51a6af 100644
--- a/include/net/xsk_buff_pool.h
+++ b/include/net/xsk_buff_pool.h
@@ -75,6 +75,7 @@ struct xsk_buff_pool {
 	u32 chunk_size;
 	u32 chunk_shift;
 	u32 frame_len;
+	u8 tx_metadata_len; /* inherited from xsk_sock */
 	u8 cached_need_wakeup;
 	bool uses_need_wakeup;
 	bool dma_need_sync;
diff --git a/include/uapi/linux/if_xdp.h b/include/uapi/linux/if_xdp.h
index a78a8096f4ce..2374eafff7db 100644
--- a/include/uapi/linux/if_xdp.h
+++ b/include/uapi/linux/if_xdp.h
@@ -63,6 +63,7 @@ struct xdp_mmap_offsets {
 #define XDP_UMEM_COMPLETION_RING	6
 #define XDP_STATISTICS			7
 #define XDP_OPTIONS			8
+#define XDP_TX_METADATA_LEN		9
 
 struct xdp_umem_reg {
 	__u64 addr; /* Start of packet data area */
diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index cc1e7f15fa73..c9b2daba7b6d 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -485,6 +485,7 @@ static struct sk_buff *xsk_build_skb(struct xdp_sock *xs,
 		int err;
 
 		hr = max(NET_SKB_PAD, L1_CACHE_ALIGN(dev->needed_headroom));
+		hr = max(hr, L1_CACHE_ALIGN((u32)xs->tx_metadata_len));
 		tr = dev->needed_tailroom;
 		len = desc->len;
 
@@ -493,14 +494,21 @@ static struct sk_buff *xsk_build_skb(struct xdp_sock *xs,
 			return ERR_PTR(err);
 
 		skb_reserve(skb, hr);
-		skb_put(skb, len);
+		skb_put(skb, len + xs->tx_metadata_len);
 
 		buffer = xsk_buff_raw_get_data(xs->pool, desc->addr);
+		buffer -= xs->tx_metadata_len;
+
 		err = skb_store_bits(skb, 0, buffer, len);
 		if (unlikely(err)) {
 			kfree_skb(skb);
 			return ERR_PTR(err);
 		}
+
+		if (xs->tx_metadata_len) {
+			skb_metadata_set(skb, xs->tx_metadata_len);
+			__skb_pull(skb, xs->tx_metadata_len);
+		}
 	}
 
 	skb->dev = dev;
@@ -1137,6 +1145,27 @@ static int xsk_setsockopt(struct socket *sock, int level, int optname,
 		mutex_unlock(&xs->mutex);
 		return err;
 	}
+	case XDP_TX_METADATA_LEN:
+	{
+		int val;
+
+		if (optlen < sizeof(val))
+			return -EINVAL;
+		if (copy_from_sockptr(&val, optval, sizeof(val)))
+			return -EFAULT;
+
+		if (val >= 256)
+			return -EINVAL;
+
+		mutex_lock(&xs->mutex);
+		if (xs->state != XSK_READY) {
+			mutex_unlock(&xs->mutex);
+			return -EBUSY;
+		}
+		xs->tx_metadata_len = val;
+		mutex_unlock(&xs->mutex);
+		return err;
+	}
 	default:
 		break;
 	}
diff --git a/net/xdp/xsk_buff_pool.c b/net/xdp/xsk_buff_pool.c
index 26f6d304451e..66ff9c345a67 100644
--- a/net/xdp/xsk_buff_pool.c
+++ b/net/xdp/xsk_buff_pool.c
@@ -85,6 +85,7 @@ struct xsk_buff_pool *xp_create_and_assign_umem(struct xdp_sock *xs,
 		XDP_PACKET_HEADROOM;
 	pool->umem = umem;
 	pool->addrs = umem->addrs;
+	pool->tx_metadata_len = xs->tx_metadata_len;
 	INIT_LIST_HEAD(&pool->free_list);
 	INIT_LIST_HEAD(&pool->xsk_tx_list);
 	spin_lock_init(&pool->xsk_tx_list_lock);
diff --git a/net/xdp/xsk_queue.h b/net/xdp/xsk_queue.h
index 6d40a77fccbe..c8d287c18d64 100644
--- a/net/xdp/xsk_queue.h
+++ b/net/xdp/xsk_queue.h
@@ -133,12 +133,13 @@ static inline bool xskq_cons_read_addr_unchecked(struct xsk_queue *q, u64 *addr)
 static inline bool xp_aligned_validate_desc(struct xsk_buff_pool *pool,
 					    struct xdp_desc *desc)
 {
-	u64 offset = desc->addr & (pool->chunk_size - 1);
+	u64 addr = desc->addr - pool->tx_metadata_len;
+	u64 offset = addr & (pool->chunk_size - 1);
 
 	if (offset + desc->len > pool->chunk_size)
 		return false;
 
-	if (desc->addr >= pool->addrs_cnt)
+	if (addr >= pool->addrs_cnt)
 		return false;
 
 	if (desc->options)
@@ -149,7 +150,7 @@ static inline bool xp_aligned_validate_desc(struct xsk_buff_pool *pool,
 static inline bool xp_unaligned_validate_desc(struct xsk_buff_pool *pool,
 					      struct xdp_desc *desc)
 {
-	u64 addr = xp_unaligned_add_offset_to_addr(desc->addr);
+	u64 addr = xp_unaligned_add_offset_to_addr(desc->addr) - pool->tx_metadata_len;
 
 	if (desc->len > pool->chunk_size)
 		return false;
-- 
2.41.0.162.gfafddb0af9-goog