[RFC PATCH net-next v1 2/4] net: introduce abstraction for network memory

[Mina Almasry]

Add the netmem_t type, an abstraction for network memory.

To add support for new memory types to the net stack, we must first
abstract the current memory type from the net stack. Currently parts of
the net stack use struct page directly:

- page_pool
- drivers
- skb_frag_t

Originally the plan was to reuse struct page* for the new memory types,
and to set the LSB on the page* to indicate it's not really a page.
However, for compiler type checking we need to introduce a new type.

netmem_t is introduced to abstract the underlying memory type. Currently
it's a no-op abstraction that is always a struct page underneath. In
parallel there is an undergoing effort to add support for devmem to the
net stack:

https://lore.kernel.org/netdev/20231208005250.2910004-1-almasrymina@xxxxxxxxxx/

Signed-off-by: Mina Almasry <almasrymina@xxxxxxxxxx>
---
 include/net/netmem.h | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)
 create mode 100644 include/net/netmem.h

diff --git a/include/net/netmem.h b/include/net/netmem.h
new file mode 100644
index 000000000000..e4309242d8be
--- /dev/null
+++ b/include/net/netmem.h
@@ -0,0 +1,35 @@
+/* SPDX-License-Identifier: GPL-2.0
+ *
+ * netmem.h
+ *	Author:	Mina Almasry <almasrymina@xxxxxxxxxx>
+ *	Copyright (C) 2023 Google LLC
+ */
+
+#ifndef _NET_NETMEM_H
+#define _NET_NETMEM_H
+
+struct netmem {
+	union {
+		struct page page;
+
+		/* Stub to prevent compiler implicitly converting from page*
+		 * to netmem_t* and vice versa.
+		 *
+		 * Other memory type(s) net stack would like to support
+		 * can be added to this union.
+		 */
+		void *addr;
+	};
+};
+
+static inline struct page *netmem_to_page(struct netmem *netmem)
+{
+	return &netmem->page;
+}
+
+static inline struct netmem *page_to_netmem(struct page *page)
+{
+	return (struct netmem *)page;
+}
+
+#endif /* _NET_NETMEM_H */
-- 
2.43.0.472.g3155946c3a-goog