[NET]: convert network timestamps to ktime_t

We currently use a special structure (struct skb_timeval) and plain
'struct timeval' to store packet timestamps in sk_buffs and struct
sock.

This has some drawbacks :
- Fixed resolution of micro second.
- Waste of space on 64bit platforms where sizeof(struct timeval)=16

I suggest using ktime_t that is a nice abstraction of high resolution
time services, currently capable of nanosecond resolution.

As sizeof(ktime_t) is 8 bytes, using ktime_t in 'struct sock' permits
a 8 byte shrink of this structure on 64bit architectures. Some other
structures also benefit from this size reduction (struct ipq in
ipv4/ip_fragment.c, struct frag_queue in ipv6/reassembly.c, ...)

Once this ktime infrastructure adopted, we can more easily provide
nanosecond resolution on top of it. (ioctl SIOCGSTAMPNS and/or
SO_TIMESTAMPNS/SCM_TIMESTAMPNS)

Note : this patch includes a bug correction in
compat_sock_get_timestamp() where a "err = 0;" was missing (so this
syscall returned -ENOENT instead of 0)

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
CC: Stephen Hemminger <shemminger@linux-foundation.org>
CC: John find <linux.kernel@free.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 14 insertions, 30 deletions

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 5992f65..f9441b5 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -27,6 +27,7 @@
 #include <net/checksum.h>
 #include <linux/rcupdate.h>
 #include <linux/dmaengine.h>
+#include <linux/hrtimer.h>
 
 #define HAVE_ALLOC_SKB		/* For the drivers to know */
 #define HAVE_ALIGNABLE_SKB	/* Ditto 8)		   */
@@ -156,11 +157,6 @@ struct skb_shared_info {
 #define SKB_DATAREF_SHIFT 16
 #define SKB_DATAREF_MASK ((1 << SKB_DATAREF_SHIFT) - 1)
 
-struct skb_timeval {
-	u32	off_sec;
-	u32	off_usec;
-};
-
 
 enum {
 	SKB_FCLONE_UNAVAILABLE,
@@ -233,7 +229,7 @@ struct sk_buff {
 	struct sk_buff		*prev;
 
 	struct sock		*sk;
-	struct skb_timeval	tstamp;
+	ktime_t			tstamp;
 	struct net_device	*dev;
 	int			iif;
 	/* 4 byte hole on 64 bit*/
@@ -1365,26 +1361,14 @@ extern void skb_add_mtu(int mtu);
  */
 static inline void skb_get_timestamp(const struct sk_buff *skb, struct timeval *stamp)
 {
-	stamp->tv_sec  = skb->tstamp.off_sec;
-	stamp->tv_usec = skb->tstamp.off_usec;
+	*stamp = ktime_to_timeval(skb->tstamp);
 }
 
-/**
- * 	skb_set_timestamp - set timestamp of a skb
- *	@skb: skb to set stamp of
- *	@stamp: pointer to struct timeval to get stamp from
- *
- *	Timestamps are stored in the skb as offsets to a base timestamp.
- *	This function converts a struct timeval to an offset and stores
- *	it in the skb.
- */
-static inline void skb_set_timestamp(struct sk_buff *skb, const struct timeval *stamp)
+static inline void __net_timestamp(struct sk_buff *skb)
 {
-	skb->tstamp.off_sec  = stamp->tv_sec;
-	skb->tstamp.off_usec = stamp->tv_usec;
+	skb->tstamp = ktime_get_real();
 }
 
-extern void __net_timestamp(struct sk_buff *skb);
 
 extern __sum16 __skb_checksum_complete(struct sk_buff *skb);
 
diff --git a/include/net/sock.h b/include/net/sock.h
index a3366c3..9583639 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -244,7 +244,7 @@ struct sock {
 	struct sk_filter      	*sk_filter;
 	void			*sk_protinfo;
 	struct timer_list	sk_timer;
-	struct timeval		sk_stamp;
+	ktime_t			sk_stamp;
 	struct socket		*sk_socket;
 	void			*sk_user_data;
 	struct page		*sk_sndmsg_page;
@@ -1307,19 +1307,19 @@ static inline int sock_intr_errno(long timeo)
 static __inline__ void
 sock_recv_timestamp(struct msghdr *msg, struct sock *sk, struct sk_buff *skb)
 {
-	struct timeval stamp;
+	ktime_t kt = skb->tstamp;
 
-	skb_get_timestamp(skb, &stamp);
 	if (sock_flag(sk, SOCK_RCVTSTAMP)) {
+		struct timeval tv;
 		/* Race occurred between timestamp enabling and packet
 		   receiving.  Fill in the current time for now. */
-		if (stamp.tv_sec == 0)
-			do_gettimeofday(&stamp);
-		skb_set_timestamp(skb, &stamp);
-		put_cmsg(msg, SOL_SOCKET, SO_TIMESTAMP, sizeof(struct timeval),
-			 &stamp);
+		if (kt.tv64 == 0)
+			kt = ktime_get_real();
+		skb->tstamp = kt;
+		tv = ktime_to_timeval(kt);
+		put_cmsg(msg, SOL_SOCKET, SO_TIMESTAMP, sizeof(tv), &tv);
 	} else
-		sk->sk_stamp = stamp;
+		sk->sk_stamp = kt;
 }
 
 /**