All available gso_type flags are currently in use, so
extend gso_type from 'unsigned short' to 'unsigned int'
to be able to add further flags.
We also reorder the struct skb_shared_info to use
two bytes of the four byte hole before dataref.
All fields before _unused are cleared now, i.e.
two bytes more than before the change.
Structure layout on x86-64 before the change:
struct skb_shared_info {
unsigned char nr_frags; /* 0 1 */
__u8 tx_flags; /* 1 1 */
short unsigned int gso_size; /* 2 2 */
short unsigned int gso_segs; /* 4 2 */
short unsigned int gso_type; /* 6 2 */
struct sk_buff * frag_list; /* 8 8 */
struct skb_shared_hwtstamps hwtstamps; /* 16 8 */
u32 tskey; /* 24 4 */
__be32 ip6_frag_id; /* 28 4 */
atomic_t dataref; /* 32 4 */
/* XXX 4 bytes hole, try to pack */
void * destructor_arg; /* 40 8 */
skb_frag_t frags[17]; /* 48 272 */
/* --- cacheline 5 boundary (320 bytes) --- */
/* size: 320, cachelines: 5, members: 12 */
/* sum members: 316, holes: 1, sum holes: 4 */
};
Structure layout on x86-64 after the change:
struct skb_shared_info {
struct sk_buff * frag_list; /* 0 8 */
struct skb_shared_hwtstamps hwtstamps; /* 8 8 */
u32 tskey; /* 16 4 */
__be32 ip6_frag_id; /* 20 4 */
unsigned int gso_type; /* 24 4 */
unsigned char nr_frags; /* 28 1 */
__u8 tx_flags; /* 29 1 */
short unsigned int gso_size; /* 30 2 */
short unsigned int gso_segs; /* 32 2 */
short unsigned int _unused; /* 34 2 */
atomic_t dataref; /* 36 4 */
void * destructor_arg; /* 40 8 */
skb_frag_t frags[17]; /* 48 272 */
/* --- cacheline 5 boundary (320 bytes) --- */
/* size: 320, cachelines: 5, members: 13 */
};
Signed-off-by: Steffen Klassert <steffen.klass...@secunet.com>
---
include/linux/skbuff.h | 13 +++++++------
net/core/skbuff.c | 2 +-
2 files changed, 8 insertions(+), 7 deletions(-)
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index c776abd..cb36159 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -413,20 +413,21 @@ struct ubuf_info {
* the end of the header data, ie. at skb->end.
*/
struct skb_shared_info {
+ struct sk_buff *frag_list;
+ struct skb_shared_hwtstamps hwtstamps;
+ u32 tskey;
+ __be32 ip6_frag_id;
+ unsigned int gso_type;
unsigned char nr_frags;
__u8 tx_flags;
unsigned short gso_size;
/* Warning: this field is not always filled in (UFO)! */
unsigned short gso_segs;
- unsigned short gso_type;
- struct sk_buff *frag_list;
- struct skb_shared_hwtstamps hwtstamps;
- u32 tskey;
- __be32 ip6_frag_id;
/*
- * Warning : all fields before dataref are cleared in __alloc_skb()
+ * Warning : all fields before _unused are cleared in __alloc_skb()
*/
+ unsigned short _unused;
atomic_t dataref;
/* Intermediate layers must ensure that destructor_arg
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 9f78109..8796b93 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -257,7 +257,7 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t
gfp_mask,
/* make sure we initialize shinfo sequentially */
shinfo = skb_shinfo(skb);
- memset(shinfo, 0, offsetof(struct skb_shared_info, dataref));
+ memset(shinfo, 0, offsetof(struct skb_shared_info, _unused));
atomic_set(&shinfo->dataref, 1);
kmemcheck_annotate_variable(shinfo->destructor_arg);
--
2.7.4
