[PATCH v10] y2038: Provide conversion helpers for struct __timespec64

[Lukasz Majewski <lukma at denx dot de>]

Those functions allow easy conversion between Y2038 safe struct
__timespec64 and other time related data structures (like struct timeval
or struct timespec).

* include/time.h (valid_timeval_to_timespec64): Add.
* include/time.h (valid_timespec_to_timespec64): Likewise.
* include/time.h (valid_timespec64_to_timespec): Likewise.
* include/time.h (valid_timespec64_to_timeval): Likewise.

---
Changes for v10:
- Provide only conversion functions to work on "valid" time structures
  (no need to provide any excessive checks)
- Return values instead of pointers

Changes for v9:
- Update comments to be more concise and describe return values from
  conversion functions (according to Joseph's request).

Changes for v8:
- None

Changes for v7:
- None

Changes for v6:
- Remove the #ifdef guard on __ASSUME_TIME64_SYSCALLS as those functions
  may be needed for fallback execution paths (on e.g. __clock_settime64).

Changes for v5:
- This code is now only compiled in when __ASSUME_TIME64_SYSCALLS is NOT
  defined. Previously it was depending on #if __TIMESIZE != 64.

Changes for v4:
- None

Changes for v3:
- Remove misleading comments regarding clearing tv_pad values during
  conversion (as Linux kernel on its own ignores upper 32 bits of tv_nsec).

Changes for v3:
- Remove timespec64_clear_padding function - as kernel ignores upper 32
  bits of tv_nsec when passed via syscall to the Linux kernel

Changes for v2:
- Add timespec64_clear_padding function
---
 include/time.h | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)

diff --git a/include/time.h b/include/time.h
index 9727786634..9878c2b2ca 100644
--- a/include/time.h
+++ b/include/time.h
@@ -178,5 +178,54 @@ in_time_t_range (__time64_t t)
   return s == t;
 }
 
+/* Convert a known valid struct timeval into a struct __timespec64.  */
+static inline struct __timespec64
+valid_timeval_to_timespec64 (const struct timeval tv)
+{
+  struct __timespec64 ts64;
+
+  ts64.tv_sec = tv.tv_sec;
+  ts64.tv_nsec = tv.tv_usec * 1000;
+
+  return ts64;
+}
+
+/* Convert a known valid struct timespec into a struct __timespec64.  */
+static inline struct __timespec64
+valid_timespec_to_timespec64 (const struct timespec ts)
+{
+  struct __timespec64 ts64;
+
+  ts64.tv_sec = ts.tv_sec;
+  ts64.tv_nsec = ts.tv_nsec;
+
+  return ts64;
+}
+
+/* Convert a valid and within range of struct timespec, struct
+   __timespec64 into a struct timespec.  */
+static inline struct timespec
+valid_timespec64_to_timespec (const struct __timespec64 ts64)
+{
+  struct timespec ts;
+
+  ts.tv_sec = (time_t) ts64.tv_sec;
+  ts.tv_nsec = ts64.tv_nsec;
+
+  return ts;
+}
+
+/* Convert a valid and within range of struct timeval struct
+   __timespec64 into a struct timeval.  */
+static inline struct timeval
+valid_timespec64_to_timeval (const struct __timespec64 ts64)
+{
+  struct timeval tv;
+
+  tv.tv_sec = (time_t) ts64.tv_sec;
+  tv.tv_usec = ts64.tv_nsec / 1000;
+
+  return tv;
+}
 #endif
 #endif
-- 
2.20.1