xdp: Simplify xdp_return_{frame, frame_rx_napi, buff}

The xdp_return_{frame,frame_rx_napi,buff} function are never used,
except in xdp_convert_zc_to_xdp_frame(), by the MEM_TYPE_XSK_BUFF_POOL
memory type.

To simplify and reduce code, change so that
xdp_convert_zc_to_xdp_frame() calls xsk_buff_free() directly since the
type is know, and remove MEM_TYPE_XSK_BUFF_POOL from the switch
statement in __xdp_return() function.
Suggested-by: Maxim Mikityanskiy <maximmi@mellanox.com>
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200520192103.355233-14-bjorn.topel@gmail.com

net/core/xdp.c

@@ -335,10 +335,11 @@ EXPORT_SYMBOL_GPL(xdp_rxq_info_reg_mem_model);
  * scenarios (e.g. queue full), it is possible to return the xdp_frame
  * while still leveraging this protection.  The @napi_direct boolean
  * is used for those calls sites.  Thus, allowing for faster recycling
- * of xdp_frames/pages in those cases.
+ * of xdp_frames/pages in those cases. This path is never used by the
+ * MEM_TYPE_XSK_BUFF_POOL memory type, so it's explicitly not part of
+ * the switch-statement.
  */
-static void __xdp_return(void *data, struct xdp_mem_info *mem, bool napi_direct,
-			 struct xdp_buff *xdp)
+static void __xdp_return(void *data, struct xdp_mem_info *mem, bool napi_direct)
 {
 	struct xdp_mem_allocator *xa;
 	struct page *page;
@@ -360,33 +361,29 @@ static void __xdp_return(void *data, struct xdp_mem_info *mem, bool napi_direct,
 		page = virt_to_page(data); /* Assumes order0 page*/
 		put_page(page);
 		break;
-	case MEM_TYPE_XSK_BUFF_POOL:
-		/* NB! Only valid from an xdp_buff! */
-		xsk_buff_free(xdp);
-		break;
 	default:
 		/* Not possible, checked in xdp_rxq_info_reg_mem_model() */
+		WARN(1, "Incorrect XDP memory type (%d) usage", mem->type);
 		break;
 	}
 }
 
 void xdp_return_frame(struct xdp_frame *xdpf)
 {
-	__xdp_return(xdpf->data, &xdpf->mem, false, NULL);
+	__xdp_return(xdpf->data, &xdpf->mem, false);
 }
 EXPORT_SYMBOL_GPL(xdp_return_frame);
 
 void xdp_return_frame_rx_napi(struct xdp_frame *xdpf)
 {
-	__xdp_return(xdpf->data, &xdpf->mem, true, NULL);
+	__xdp_return(xdpf->data, &xdpf->mem, true);
 }
 EXPORT_SYMBOL_GPL(xdp_return_frame_rx_napi);
 
 void xdp_return_buff(struct xdp_buff *xdp)
 {
-	__xdp_return(xdp->data, &xdp->rxq->mem, true, xdp);
+	__xdp_return(xdp->data, &xdp->rxq->mem, true);
 }
-EXPORT_SYMBOL_GPL(xdp_return_buff);
 
 /* Only called for MEM_TYPE_PAGE_POOL see xdp.h */
 void __xdp_release_frame(void *data, struct xdp_mem_info *mem)
@@ -467,7 +464,7 @@ struct xdp_frame *xdp_convert_zc_to_xdp_frame(struct xdp_buff *xdp)
 	xdpf->metasize = metasize;
 	xdpf->mem.type = MEM_TYPE_PAGE_ORDER0;
 
-	xdp_return_buff(xdp);
+	xsk_buff_free(xdp);
 	return xdpf;
 }
 EXPORT_SYMBOL_GPL(xdp_convert_zc_to_xdp_frame);