skbuff: add flags to ubuf_info for ubuf setup

Currently, when an ubuf is attached to a new skb, the shared
flags word is initialized to a fixed value.  Instead of doing
this, set the default flags in the ubuf, and have new skbs
inherit from this default.

This is needed when setting up different zerocopy types.
Signed-off-by: Jonathan Lemon <jonathan.lemon@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/linux/skbuff.h

@@ -480,6 +480,7 @@ struct ubuf_info {
 		};
 	};
 	refcount_t refcnt;
+	u8 flags;
 
 	struct mmpin {
 		struct user_struct *user;
@@ -1456,7 +1457,7 @@ static inline void skb_zcopy_set(struct sk_buff *skb, struct ubuf_info *uarg,
 		else
 			skb_zcopy_get(uarg);
 		skb_shinfo(skb)->destructor_arg = uarg;
-		skb_shinfo(skb)->flags |= SKBFL_ZEROCOPY_FRAG;
+		skb_shinfo(skb)->flags |= uarg->flags;
 	}
 }
 

net/core/skbuff.c

@@ -1119,6 +1119,7 @@ struct ubuf_info *msg_zerocopy_alloc(struct sock *sk, size_t size)
 	uarg->len = 1;
 	uarg->bytelen = size;
 	uarg->zerocopy = 1;
+	uarg->flags = SKBFL_ZEROCOPY_FRAG;
 	refcount_set(&uarg->refcnt, 1);
 	sock_hold(sk);