xsk: allow core/drivers to test EOP bit

Drivers are used to check for EOP bit whereas AF_XDP operates on
inverted logic - user space indicates that current frag is not the last
one and packet continues. For AF_XDP core needs, add xp_mb_desc() that
will simply test XDP_PKT_CONTD from xdp_desc::options, but in order to
preserve drivers default behavior, introduce an interface for ZC drivers
that will negate xp_mb_desc() result and therefore make it easier to
test EOP bit from during production of HW Tx descriptors.

Signed-off-by: Maciej Fijalkowski <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

Author: mfijalko

include/net/xdp_sock_drv.h

@@ -89,6 +89,11 @@ static inline struct xdp_buff *xsk_buff_alloc(struct xsk_buff_pool *pool)
 	return xp_alloc(pool);
 }
 
+static inline bool xsk_is_eop_desc(struct xdp_desc *desc)
+{
+	return !xp_mb_desc(desc);
+}
+
 /* Returns as many entries as possible up to max. 0 <= N <= max. */
 static inline u32 xsk_buff_alloc_batch(struct xsk_buff_pool *pool, struct xdp_buff **xdp, u32 max)
 {
@@ -241,6 +246,11 @@ static inline struct xdp_buff *xsk_buff_alloc(struct xsk_buff_pool *pool)
 	return NULL;
 }
 
+static inline bool xsk_is_eop_desc(struct xdp_desc *desc)
+{
+	return false;
+}
+
 static inline u32 xsk_buff_alloc_batch(struct xsk_buff_pool *pool, struct xdp_buff **xdp, u32 max)
 {
 	return 0;

include/net/xsk_buff_pool.h

@@ -184,6 +184,11 @@ static inline bool xp_desc_crosses_non_contig_pg(struct xsk_buff_pool *pool,
 	       !(pool->dma_pages[addr >> PAGE_SHIFT] & XSK_NEXT_PG_CONTIG_MASK);
 }
 
+static inline bool xp_mb_desc(struct xdp_desc *desc)
+{
+	return desc->options & XDP_PKT_CONTD;
+}
+
 static inline u64 xp_aligned_extract_addr(struct xsk_buff_pool *pool, u64 addr)
 {
 	return addr & pool->chunk_mask;