nfs: use time64_t internally

The timestamps for the cache are all in boottime seconds, so they
don't overflow 32-bit values, but the use of time_t is deprecated
because it generally does overflow when used with wall-clock time.

There are multiple possible ways of avoiding it:

- leave time_t, which is safe here, but forces others to
  look into this code to determine that it is over and over.

- use a more generic type, like 'int' or 'long', which is known
  to be sufficient here but loses the documentation of referring
  to timestamps

- use ktime_t everywhere, and convert into seconds in the few
  places where we want realtime-seconds. The conversion is
  sometimes expensive, but not more so than the conversion we
  do today.

- use time64_t to clarify that this code is safe. Nothing would
  change for 64-bit architectures, but it is slightly less
  efficient on 32-bit architectures.

Without a clear winner of the three approaches above, this picks
the last one, favouring readability over a small performance
loss on 32-bit architectures.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>

1 files changed, 23 insertions, 19 deletions

diff --git a/include/linux/sunrpc/cache.h b/include/linux/sunrpc/cache.h
index f8603724fbee..0f64de7caa39 100644
--- a/include/linux/sunrpc/cache.h
+++ b/include/linux/sunrpc/cache.h
@@ -45,8 +45,8 @@
  */
 struct cache_head {
 	struct hlist_node	cache_list;
-	time_t		expiry_time;	/* After time time, don't use the data */
-	time_t		last_refresh;   /* If CACHE_PENDING, this is when upcall was
+	time64_t	expiry_time;	/* After time time, don't use the data */
+	time64_t	last_refresh;   /* If CACHE_PENDING, this is when upcall was
 					 * sent, else this is when update was
 					 * received, though it is alway set to
 					 * be *after* ->flush_time.
@@ -95,22 +95,22 @@ struct cache_detail {
 	/* fields below this comment are for internal use
 	 * and should not be touched by cache owners
 	 */
-	time_t			flush_time;		/* flush all cache items with
+	time64_t		flush_time;		/* flush all cache items with
 							 * last_refresh at or earlier
 							 * than this.  last_refresh
 							 * is never set at or earlier
 							 * than this.
 							 */
 	struct list_head	others;
-	time_t			nextcheck;
+	time64_t		nextcheck;
 	int			entries;
 
 	/* fields for communication over channel */
 	struct list_head	queue;
 
 	atomic_t		writers;		/* how many time is /channel open */
-	time_t			last_close;		/* if no writers, when did last close */
-	time_t			last_warn;		/* when we last warned about no writers */
+	time64_t		last_close;		/* if no writers, when did last close */
+	time64_t		last_warn;		/* when we last warned about no writers */
 
 	union {
 		struct proc_dir_entry	*procfs;
@@ -147,18 +147,22 @@ struct cache_deferred_req {
  * timestamps kept in the cache are expressed in seconds
  * since boot.  This is the best for measuring differences in
  * real time.
+ * This reimplemnts ktime_get_boottime_seconds() in a slightly
+ * faster but less accurate way. When we end up converting
+ * back to wallclock (CLOCK_REALTIME), that error often
+ * cancels out during the reverse operation.
  */
-static inline time_t seconds_since_boot(void)
+static inline time64_t seconds_since_boot(void)
 {
-	struct timespec boot;
-	getboottime(&boot);
-	return get_seconds() - boot.tv_sec;
+	struct timespec64 boot;
+	getboottime64(&boot);
+	return ktime_get_real_seconds() - boot.tv_sec;
 }
 
-static inline time_t convert_to_wallclock(time_t sinceboot)
+static inline time64_t convert_to_wallclock(time64_t sinceboot)
 {
-	struct timespec boot;
-	getboottime(&boot);
+	struct timespec64 boot;
+	getboottime64(&boot);
 	return boot.tv_sec + sinceboot;
 }
 
@@ -273,7 +277,7 @@ static inline int get_uint(char **bpp, unsigned int *anint)
 	return 0;
 }
 
-static inline int get_time(char **bpp, time_t *time)
+static inline int get_time(char **bpp, time64_t *time)
 {
 	char buf[50];
 	long long ll;
@@ -287,20 +291,20 @@ static inline int get_time(char **bpp, time_t *time)
 	if (kstrtoll(buf, 0, &ll))
 		return -EINVAL;
 
-	*time = (time_t)ll;
+	*time = ll;
 	return 0;
 }
 
-static inline time_t get_expiry(char **bpp)
+static inline time64_t get_expiry(char **bpp)
 {
-	time_t rv;
-	struct timespec boot;
+	time64_t rv;
+	struct timespec64 boot;
 
 	if (get_time(bpp, &rv))
 		return 0;
 	if (rv < 0)
 		return 0;
-	getboottime(&boot);
+	getboottime64(&boot);
 	return rv - boot.tv_sec;
 }