net: introduce struct ubuf_info_msgzc

We're going to split struct ubuf_info and leave there only
mandatory fields. Users are free to extend it. Add struct
ubuf_info_msgzc, which will be an extended version for MSG_ZEROCOPY and
some other users. It duplicates of struct ubuf_info for now and will be
removed in a couple of patches.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Acked-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/linux/skbuff.h

@@ -554,7 +554,28 @@ struct ubuf_info {
 	} mmp;
 };
 
+struct ubuf_info_msgzc {
+	struct ubuf_info ubuf;
+
+	union {
+		struct {
+			unsigned long desc;
+			void *ctx;
+		};
+		struct {
+			u32 id;
+			u16 len;
+			u16 zerocopy:1;
+			u32 bytelen;
+		};
+	};
+
+	struct mmpin mmp;
+};
+
 #define skb_uarg(SKB)	((struct ubuf_info *)(skb_shinfo(SKB)->destructor_arg))
+#define uarg_to_msgzc(ubuf_ptr)	container_of((ubuf_ptr), struct ubuf_info_msgzc, \
+					     ubuf)
 
 int mm_account_pinned_pages(struct mmpin *mmp, size_t size);
 void mm_unaccount_pinned_pages(struct mmpin *mmp);