Subject: [RFC PATCH v3 12/12] tap/tun: add skb_zcopy_init() helper for initialization.

From: Jonathan Lemon <[email-masked]>
Date: Wed, 30 Dec 2020 11:12:44 -0800

From: Jonathan Lemon <[email-masked]>

Replace direct assignments with skb_zcopy_init() for zerocopy
cases where a new skb is initialized, without changing the
reference counts.

Signed-off-by: Jonathan Lemon <[email-masked]>
---
 drivers/net/tap.c      | 3 +--
 drivers/net/tun.c      | 3 +--
 drivers/vhost/net.c    | 1 +
 include/linux/skbuff.h | 9 +++++++--
 4 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/drivers/net/tap.c b/drivers/net/tap.c
index f7a19d9b7c27..3c652c8ac5ba 100644
--- a/drivers/net/tap.c
+++ b/drivers/net/tap.c
@@ -722,8 +722,7 @@ static ssize_t tap_get_user(struct tap_queue *q, void *msg_control,
 	tap = rcu_dereference(q->tap);
 	/* copy skb_ubuf_info for callback when skb has no error */
 	if (zerocopy) {
-		skb_shinfo(skb)->destructor_arg = msg_control;
-		skb_shinfo(skb)->flags |= SKBFL_ZEROCOPY_FRAG;
+		skb_zcopy_init(skb, msg_control);
 	} else if (msg_control) {
 		struct ubuf_info *uarg = msg_control;
 		uarg->callback(NULL, uarg, false);
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index dd9edbd72ae8..7414e0584729 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1814,8 +1814,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
 
 	/* copy skb_ubuf_info for callback when skb has no error */
 	if (zerocopy) {
-		skb_shinfo(skb)->destructor_arg = msg_control;
-		skb_shinfo(skb)->flags |= SKBFL_ZEROCOPY_FRAG;
+		skb_zcopy_init(skb, msg_control);
 	} else if (msg_control) {
 		struct ubuf_info *uarg = msg_control;
 		uarg->callback(NULL, uarg, false);
diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index bf28d0b75c1b..5c722c4179a9 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -904,6 +904,7 @@ static void handle_tx_zerocopy(struct vhost_net *net, struct socket *sock)
 			ubuf->callback = vhost_zerocopy_callback;
 			ubuf->ctx = nvq->ubufs;
 			ubuf->desc = nvq->upend_idx;
+			ubuf->flags = SKBFL_ZEROCOPY_FRAG;
 			refcount_set(&ubuf->refcnt, 1);
 			msg.msg_control = &ctl;
 			ctl.type = TUN_MSG_UBUF;
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 58010df9d183..3ec8b83aca3e 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1448,6 +1448,12 @@ static inline void skb_zcopy_get(struct ubuf_info *uarg)
 	refcount_inc(&uarg->refcnt);
 }
 
+static inline void skb_zcopy_init(struct sk_buff *skb, struct ubuf_info *uarg)
+{
+	skb_shinfo(skb)->destructor_arg = uarg;
+	skb_shinfo(skb)->flags |= uarg->flags;
+}
+
 static inline void skb_zcopy_set(struct sk_buff *skb, struct ubuf_info *uarg,
 				 bool *have_ref)
 {
@@ -1456,8 +1462,7 @@ static inline void skb_zcopy_set(struct sk_buff *skb, struct ubuf_info *uarg,
 			*have_ref = false;
 		else
 			skb_zcopy_get(uarg);
-		skb_shinfo(skb)->destructor_arg = uarg;
-		skb_shinfo(skb)->flags |= uarg->flags;
+		skb_zcopy_init(skb, uarg);
 	}
 }
 
-- 
2.24.1