xsk: introduce wrappers and helpers for supporting multi-buffer in Tx path

In Tx path, xsk core reserves space for each desc to be transmitted in
the completion queue and it's address contained in it is stored in the
skb destructor arg. After successful transmission the skb destructor
submits the addr marking completion.

To handle multiple descriptors per packet, now along with reserving
space for each descriptor, the corresponding address is also stored in
completion queue. The number of pending descriptors are stored in skb
destructor arg and is used by the skb destructor to update completions.

Introduce 'skb' in xdp_sock to store a partially built packet when
__xsk_generic_xmit() must return before it sees the EOP descriptor for
the current packet so that packet building can resume in next call of
__xsk_generic_xmit().

Helper functions are introduced to set and get the pending descriptors
in the skb destructor arg. Also, wrappers are introduced for storing
descriptor addresses, submitting and cancelling (for unsuccessful
transmissions) the number of completions.

Signed-off-by: Tirthendu Sarkar <tirthendu.sarkar@intel.com>
Link: https://lore.kernel.org/r/20230719132421.584801-7-maciej.fijalkowski@intel.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/include/net/xdp_sock.h b/include/net/xdp_sock.h
index 36b0411a0d1b..1617af380162 100644
--- a/include/net/xdp_sock.h
+++ b/include/net/xdp_sock.h
@@ -68,6 +68,12 @@ struct xdp_sock {
 	u64 rx_dropped;
 	u64 rx_queue_full;
 
+	/* When __xsk_generic_xmit() must return before it sees the EOP descriptor for the current
+	 * packet, the partially built skb is saved here so that packet building can resume in next
+	 * call of __xsk_generic_xmit().
+	 */
+	struct sk_buff *skb;
+
 	struct list_head map_list;
 	/* Protects map_list */
 	spinlock_t map_list_lock;