[Support/FileSystem] Add sub-second precision for atime/mtime of sys::fs::file_status on unix platforms

Summary:
getLastAccessedTime() and getLastModificationTime() provided times in nanoseconds but with only 1 second resolution, even when the underlying file system could provide more precise times than that.
These changes add sub-second precision for unix platforms that support improved precision.

Also add some comments to make sure people are aware that the resolution of times can vary across different file systems.

Reviewers: labath, zturner, aaron.ballman, kristina

Reviewed By: aaron.ballman, kristina

Subscribers: lebedev.ri, mgorny, kristina, llvm-commits

Differential Revision: https://reviews.llvm.org/D54826

llvm-svn: 347530

5 files changed, 61 insertions, 9 deletions

diff --git a/llvm/cmake/config-ix.cmake b/llvm/cmake/config-ix.cmake
index 4bf2a9e9112..900c35ee4f0 100644
--- a/llvm/cmake/config-ix.cmake
+++ b/llvm/cmake/config-ix.cmake
@@ -7,6 +7,7 @@ include(CheckIncludeFile)
 include(CheckLibraryExists)
 include(CheckSymbolExists)
 include(CheckFunctionExists)
+include(CheckStructHasMember)
 include(CheckCCompilerFlag)
 
 include(CheckCompilerVersion)
@@ -248,6 +249,11 @@ if( HAVE_DLFCN_H )
   endif()
 endif()
 
+CHECK_STRUCT_HAS_MEMBER("struct stat" st_mtimespec.tv_nsec
+    "sys/types.h;sys/stat.h" HAVE_STRUCT_STAT_ST_MTIMESPEC_TV_NSEC)
+CHECK_STRUCT_HAS_MEMBER("struct stat" st_mtim.tv_nsec
+    "sys/types.h;sys/stat.h" HAVE_STRUCT_STAT_ST_MTIM_TV_NSEC)
+
 check_symbol_exists(__GLIBC__ stdio.h LLVM_USING_GLIBC)
 if( LLVM_USING_GLIBC )
   add_definitions( -D_GNU_SOURCE )
diff --git a/llvm/include/llvm/Config/config.h.cmake b/llvm/include/llvm/Config/config.h.cmake
index aece421b77d..03bbd74d6d3 100644
--- a/llvm/include/llvm/Config/config.h.cmake
+++ b/llvm/include/llvm/Config/config.h.cmake
@@ -208,6 +208,12 @@
 /* Define to 1 if you have the <sys/time.h> header file. */
 #cmakedefine HAVE_SYS_TIME_H ${HAVE_SYS_TIME_H}
 
+/* Define to 1 if stat struct has st_mtimespec member .*/
+#cmakedefine HAVE_STRUCT_STAT_ST_MTIMESPEC_TV_NSEC ${HAVE_STRUCT_STAT_ST_MTIMESPEC_TV_NSEC}
+
+/* Define to 1 if stat struct has st_mtim member. */
+#cmakedefine HAVE_STRUCT_STAT_ST_MTIM_TV_NSEC ${HAVE_STRUCT_STAT_ST_MTIM_TV_NSEC}
+
 /* Define to 1 if you have the <sys/types.h> header file. */
 #cmakedefine HAVE_SYS_TYPES_H ${HAVE_SYS_TYPES_H}
 
diff --git a/llvm/include/llvm/Support/Chrono.h b/llvm/include/llvm/Support/Chrono.h
index 994068af377..57677e8d5cf 100644
--- a/llvm/include/llvm/Support/Chrono.h
+++ b/llvm/include/llvm/Support/Chrono.h
@@ -47,6 +47,14 @@ toTimePoint(std::time_t T) {
   return time_point_cast<seconds>(system_clock::from_time_t(T));
 }
 
+/// Convert a std::time_t + nanoseconds to a TimePoint
+LLVM_ATTRIBUTE_ALWAYS_INLINE inline TimePoint<>
+toTimePoint(std::time_t T, uint32_t nsec) {
+  using namespace std::chrono;
+  return time_point_cast<nanoseconds>(system_clock::from_time_t(T))
+    + nanoseconds(nsec);
+}
+
 } // namespace sys
 
 raw_ostream &operator<<(raw_ostream &OS, sys::TimePoint<> TP);
diff --git a/llvm/include/llvm/Support/FileSystem.h b/llvm/include/llvm/Support/FileSystem.h
index 5ad39c8054f..827e2e91eea 100644
--- a/llvm/include/llvm/Support/FileSystem.h
+++ b/llvm/include/llvm/Support/FileSystem.h
@@ -160,6 +160,8 @@ protected:
   #if defined(LLVM_ON_UNIX)
   time_t fs_st_atime = 0;
   time_t fs_st_mtime = 0;
+  uint32_t fs_st_atime_nsec = 0;
+  uint32_t fs_st_mtime_nsec = 0;
   uid_t fs_st_uid = 0;
   gid_t fs_st_gid = 0;
   off_t fs_st_size = 0;
@@ -180,9 +182,12 @@ public:
   explicit basic_file_status(file_type Type) : Type(Type) {}
 
   #if defined(LLVM_ON_UNIX)
-  basic_file_status(file_type Type, perms Perms, time_t ATime, time_t MTime,
+  basic_file_status(file_type Type, perms Perms, time_t ATime,
+                    uint32_t ATimeNSec, time_t MTime, uint32_t MTimeNSec,
                     uid_t UID, gid_t GID, off_t Size)
-      : fs_st_atime(ATime), fs_st_mtime(MTime), fs_st_uid(UID), fs_st_gid(GID),
+      : fs_st_atime(ATime), fs_st_mtime(MTime),
+        fs_st_atime_nsec(ATimeNSec), fs_st_mtime_nsec(MTimeNSec),
+        fs_st_uid(UID), fs_st_gid(GID),
         fs_st_size(Size), Type(Type), Perms(Perms) {}
 #elif defined(_WIN32)
   basic_file_status(file_type Type, perms Perms, uint32_t LastAccessTimeHigh,
@@ -199,7 +204,20 @@ public:
   // getters
   file_type type() const { return Type; }
   perms permissions() const { return Perms; }
+
+  /// The file access time as reported from the underlying file system.
+  ///
+  /// Also see comments on \c getLastModificationTime() related to the precision
+  /// of the returned value.
   TimePoint<> getLastAccessedTime() const;
+
+  /// The file modification time as reported from the underlying file system.
+  ///
+  /// The returned value allows for nanosecond precision but the actual
+  /// resolution is an implementation detail of the underlying file system.
+  /// There is no guarantee for what kind of resolution you can expect, the
+  /// resolution can differ across platforms and even across mountpoints on the
+  /// same machine.
   TimePoint<> getLastModificationTime() const;
 
   #if defined(LLVM_ON_UNIX)
@@ -247,8 +265,11 @@ public:
 
   #if defined(LLVM_ON_UNIX)
   file_status(file_type Type, perms Perms, dev_t Dev, nlink_t Links, ino_t Ino,
-              time_t ATime, time_t MTime, uid_t UID, gid_t GID, off_t Size)
-      : basic_file_status(Type, Perms, ATime, MTime, UID, GID, Size),
+              time_t ATime, uint32_t ATimeNSec,
+              time_t MTime, uint32_t MTimeNSec,
+              uid_t UID, gid_t GID, off_t Size)
+      : basic_file_status(Type, Perms, ATime, ATimeNSec, MTime, MTimeNSec,
+                          UID, GID, Size),
         fs_st_dev(Dev), fs_st_nlinks(Links), fs_st_ino(Ino) {}
   #elif defined(_WIN32)
   file_status(file_type Type, perms Perms, uint32_t LinkCount,
diff --git a/llvm/lib/Support/Unix/Path.inc b/llvm/lib/Support/Unix/Path.inc
index 91549606709..d130b33f840 100644
--- a/llvm/lib/Support/Unix/Path.inc
+++ b/llvm/lib/Support/Unix/Path.inc
@@ -229,11 +229,11 @@ std::string getMainExecutable(const char *argv0, void *MainAddr) {
 }
 
 TimePoint<> basic_file_status::getLastAccessedTime() const {
-  return toTimePoint(fs_st_atime);
+  return toTimePoint(fs_st_atime, fs_st_atime_nsec);
 }
 
 TimePoint<> basic_file_status::getLastModificationTime() const {
-  return toTimePoint(fs_st_mtime);
+  return toTimePoint(fs_st_mtime, fs_st_mtime_nsec);
 }
 
 UniqueID file_status::getUniqueID() const {
@@ -591,11 +591,22 @@ static std::error_code fillStatus(int StatRet, const struct stat &Status,
     return EC;
   }
 
+  uint32_t atime_nsec, mtime_nsec;
+#if defined(HAVE_STRUCT_STAT_ST_MTIMESPEC_TV_NSEC)
+  atime_nsec = Status.st_atimespec.tv_nsec;
+  mtime_nsec = Status.st_mtimespec.tv_nsec;
+#elif defined(HAVE_STRUCT_STAT_ST_MTIM_TV_NSEC)
+  atime_nsec = Status.st_atim.tv_nsec;
+  mtime_nsec = Status.st_mtim.tv_nsec;
+#else
+  atime_nsec = mtime_nsec = 0;
+#endif
+
   perms Perms = static_cast<perms>(Status.st_mode) & all_perms;
   Result = file_status(typeForMode(Status.st_mode), Perms, Status.st_dev,
-                       Status.st_nlink, Status.st_ino, Status.st_atime,
-                       Status.st_mtime, Status.st_uid, Status.st_gid,
-                       Status.st_size);
+                       Status.st_nlink, Status.st_ino,
+                       Status.st_atime, atime_nsec, Status.st_mtime, mtime_nsec,
+                       Status.st_uid, Status.st_gid, Status.st_size);
 
   return std::error_code();
 }