time: Introduce jiffies64_to_msecs()

there is a similar helper in net/netfilter/nf_tables_api.c,
this maybe become a common request someday, so move it to
time.c
Signed-off-by: Zhang Yu <zhangyu31@baidu.com>
Signed-off-by: Li RongQing <lirongqing@baidu.com>
Acked-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/linux/jiffies.h

@@ -297,6 +297,7 @@ static inline u64 jiffies_to_nsecs(const unsigned long j)
 }
 
 extern u64 jiffies64_to_nsecs(u64 j);
+extern u64 jiffies64_to_msecs(u64 j);
 
 extern unsigned long __msecs_to_jiffies(const unsigned int m);
 #if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)

kernel/time/time.c

@@ -783,6 +783,16 @@ u64 jiffies64_to_nsecs(u64 j)
 }
 EXPORT_SYMBOL(jiffies64_to_nsecs);
 
+u64 jiffies64_to_msecs(const u64 j)
+{
+#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
+	return (MSEC_PER_SEC / HZ) * j;
+#else
+	return div_u64(j * HZ_TO_MSEC_NUM, HZ_TO_MSEC_DEN);
+#endif
+}
+EXPORT_SYMBOL(jiffies64_to_msecs);
+
 /**
  * nsecs_to_jiffies64 - Convert nsecs in u64 to jiffies64
  *

net/netfilter/nf_tables_api.c

@@ -3193,9 +3193,7 @@ static int nf_msecs_to_jiffies64(const struct nlattr *nla, u64 *result)
 
 static __be64 nf_jiffies64_to_msecs(u64 input)
 {
-	u64 ms = jiffies64_to_nsecs(input);
-
-	return cpu_to_be64(div_u64(ms, NSEC_PER_MSEC));
+	return cpu_to_be64(jiffies64_to_msecs(input));
 }
 
 static int nf_tables_fill_set(struct sk_buff *skb, const struct nft_ctx *ctx,