Subject: [RFC bpf-next 1/7] net: introduce __init_skb and __init_skb_shinfo helpers

From: Stanislav Fomichev <[email-masked]>
Date: Tue, 5 Feb 2019 09:36:23 -0800

__init_skb is essentially a version of __build_skb which accepts skb as
an argument (instead of doing kmem_cache_alloc to allocate it).

__init_skb_shinfo initializes shinfo.

No functional changes.

Signed-off-by: Stanislav Fomichev <[email-masked]>
---
 include/linux/skbuff.h |  1 +
 net/core/skbuff.c      | 68 ++++++++++++++++++++----------------------
 2 files changed, 33 insertions(+), 36 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 831846617d07..ad883ab2762c 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1001,6 +1001,7 @@ void kfree_skb_partial(struct sk_buff *skb, bool head_stolen);
 bool skb_try_coalesce(struct sk_buff *to, struct sk_buff *from,
 		      bool *fragstolen, int *delta_truesize);
 
+void __init_skb(struct sk_buff *skb, u8 *data, unsigned int size);
 struct sk_buff *__alloc_skb(unsigned int size, gfp_t priority, int flags,
 			    int node);
 struct sk_buff *__build_skb(void *data, unsigned int frag_size);
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 26d848484912..23c9cf100bd4 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -160,6 +160,34 @@ static void *__kmalloc_reserve(size_t size, gfp_t flags, int node,
  *
  */
 
+void __init_skb(struct sk_buff *skb, u8 *data, unsigned int size)
+{
+	/* Only clear those fields we need to clear, not those that we will
+	 * actually initialise below. Hence, don't put any more fields after
+	 * the tail pointer in struct sk_buff!
+	 */
+	memset(skb, 0, offsetof(struct sk_buff, tail));
+	/* Account for allocated memory : skb + skb->head */
+	skb->truesize = SKB_TRUESIZE(size);
+	refcount_set(&skb->users, 1);
+	skb->head = data;
+	skb->data = data;
+	skb_reset_tail_pointer(skb);
+	skb->end = skb->tail + size;
+	skb->mac_header = (typeof(skb->mac_header))~0U;
+	skb->transport_header = (typeof(skb->transport_header))~0U;
+}
+
+static inline void __init_skb_shinfo(struct sk_buff *skb)
+{
+	struct skb_shared_info *shinfo;
+
+	/* make sure we initialize shinfo sequentially */
+	shinfo = skb_shinfo(skb);
+	memset(shinfo, 0, offsetof(struct skb_shared_info, dataref));
+	atomic_set(&shinfo->dataref, 1);
+}
+
 /**
  *	__alloc_skb	-	allocate a network buffer
  *	@size: size to allocate
@@ -181,7 +209,6 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
 			    int flags, int node)
 {
 	struct kmem_cache *cache;
-	struct skb_shared_info *shinfo;
 	struct sk_buff *skb;
 	u8 *data;
 	bool pfmemalloc;
@@ -215,27 +242,9 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
 	size = SKB_WITH_OVERHEAD(ksize(data));
 	prefetchw(data + size);
 
-	/*
-	 * Only clear those fields we need to clear, not those that we will
-	 * actually initialise below. Hence, don't put any more fields after
-	 * the tail pointer in struct sk_buff!
-	 */
-	memset(skb, 0, offsetof(struct sk_buff, tail));
-	/* Account for allocated memory : skb + skb->head */
-	skb->truesize = SKB_TRUESIZE(size);
+	__init_skb(skb, data, size);
+	__init_skb_shinfo(skb);
 	skb->pfmemalloc = pfmemalloc;
-	refcount_set(&skb->users, 1);
-	skb->head = data;
-	skb->data = data;
-	skb_reset_tail_pointer(skb);
-	skb->end = skb->tail + size;
-	skb->mac_header = (typeof(skb->mac_header))~0U;
-	skb->transport_header = (typeof(skb->transport_header))~0U;
-
-	/* make sure we initialize shinfo sequentially */
-	shinfo = skb_shinfo(skb);
-	memset(shinfo, 0, offsetof(struct skb_shared_info, dataref));
-	atomic_set(&shinfo->dataref, 1);
 
 	if (flags & SKB_ALLOC_FCLONE) {
 		struct sk_buff_fclones *fclones;
@@ -277,7 +286,6 @@ EXPORT_SYMBOL(__alloc_skb);
  */
 struct sk_buff *__build_skb(void *data, unsigned int frag_size)
 {
-	struct skb_shared_info *shinfo;
 	struct sk_buff *skb;
 	unsigned int size = frag_size ? : ksize(data);
 
@@ -287,20 +295,8 @@ struct sk_buff *__build_skb(void *data, unsigned int frag_size)
 
 	size -= SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
 
-	memset(skb, 0, offsetof(struct sk_buff, tail));
-	skb->truesize = SKB_TRUESIZE(size);
-	refcount_set(&skb->users, 1);
-	skb->head = data;
-	skb->data = data;
-	skb_reset_tail_pointer(skb);
-	skb->end = skb->tail + size;
-	skb->mac_header = (typeof(skb->mac_header))~0U;
-	skb->transport_header = (typeof(skb->transport_header))~0U;
-
-	/* make sure we initialize shinfo sequentially */
-	shinfo = skb_shinfo(skb);
-	memset(shinfo, 0, offsetof(struct skb_shared_info, dataref));
-	atomic_set(&shinfo->dataref, 1);
+	__init_skb(skb, data, size);
+	__init_skb_shinfo(skb);
 
 	return skb;
 }
-- 
2.20.1.611.gfbb209baf1-goog