xsk: add Tx queue setup and mmap support

Another setsockopt (XDP_TX_QUEUE) is added to let the process allocate
a queue, where the user process can pass frames to be transmitted by
the kernel.

The mmapping of the queue is done using the XDP_PGOFF_TX_QUEUE offset.
Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

include/net/xdp_sock.h

@@ -30,6 +30,7 @@ struct xdp_sock {
 	struct xdp_umem *umem;
 	struct list_head flush_node;
 	u16 queue_id;
+	struct xsk_queue *tx ____cacheline_aligned_in_smp;
 	/* Protects multiple processes in the control path */
 	struct mutex mutex;
 	u64 rx_dropped;

include/uapi/linux/if_xdp.h

@@ -34,6 +34,7 @@ struct sockaddr_xdp {
 
 /* XDP socket options */
 #define XDP_RX_RING			1
+#define XDP_TX_RING			2
 #define XDP_UMEM_REG			3
 #define XDP_UMEM_FILL_RING		4
 #define XDP_UMEM_COMPLETION_RING	5
@@ -47,6 +48,7 @@ struct xdp_umem_reg {
 
 /* Pgoff for mmaping the rings */
 #define XDP_PGOFF_RX_RING			  0
+#define XDP_PGOFF_TX_RING		 0x80000000
 #define XDP_UMEM_PGOFF_FILL_RING	0x100000000
 #define XDP_UMEM_PGOFF_COMPLETION_RING	0x180000000
 

net/xdp/xsk.c

@@ -206,7 +206,7 @@ static int xsk_bind(struct socket *sock, struct sockaddr *addr, int addr_len)
 		goto out_release;
 	}
 
-	if (!xs->rx) {
+	if (!xs->rx && !xs->tx) {
 		err = -EINVAL;
 		goto out_unlock;
 	}
@@ -291,6 +291,7 @@ static int xsk_setsockopt(struct socket *sock, int level, int optname,
 
 	switch (optname) {
 	case XDP_RX_RING:
+	case XDP_TX_RING:
 	{
 		struct xsk_queue **q;
 		int entries;
@@ -301,7 +302,7 @@ static int xsk_setsockopt(struct socket *sock, int level, int optname,
 			return -EFAULT;
 
 		mutex_lock(&xs->mutex);
-		q = &xs->rx;
+		q = (optname == XDP_TX_RING) ? &xs->tx : &xs->rx;
 		err = xsk_init_queue(entries, q, false);
 		mutex_unlock(&xs->mutex);
 		return err;
@@ -372,6 +373,8 @@ static int xsk_mmap(struct file *file, struct socket *sock,
 
 	if (offset == XDP_PGOFF_RX_RING) {
 		q = xs->rx;
+	} else if (offset == XDP_PGOFF_TX_RING) {
+		q = xs->tx;
 	} else {
 		if (!xs->umem)
 			return -EINVAL;
@@ -431,6 +434,7 @@ static void xsk_destruct(struct sock *sk)
 		return;
 
 	xskq_destroy(xs->rx);
+	xskq_destroy(xs->tx);
 	xdp_put_umem(xs->umem);
 
 	sk_refcnt_debug_dec(sk);