Bug 1657663: Improve timestamp precision for nsLocalFileUnix r=froydnj,barret

This change updates the unix implementation of nsLocalFile
Set/GetLastModifiedTime methods to improve the precision of file modification
times from a 1 second resolution to a 1 millisecond resolution.

Differential Revision: https://phabricator.services.mozilla.com/D86238

old-configure.in

@@ -1128,7 +1128,7 @@ fi
 
 dnl Checks for library functions.
 dnl ========================================================
-AC_CHECK_FUNCS(stat64 lstat64 truncate64 statvfs64 statvfs statfs64 statfs getpagesize gmtime_r localtime_r arc4random arc4random_buf mallinfo gettid lchown setpriority strerror syscall)
+AC_CHECK_FUNCS(stat64 lstat64 truncate64 statvfs64 statvfs statfs64 statfs getpagesize gmtime_r localtime_r arc4random arc4random_buf mallinfo gettid lchown setpriority strerror syscall lutimes)
 
 dnl check for clock_gettime(), the CLOCK_MONOTONIC clock
 AC_CACHE_CHECK(for clock_gettime(CLOCK_MONOTONIC),

xpcom/io/nsLocalFileUnix.cpp

@@ -13,9 +13,13 @@
 #include "mozilla/DebugOnly.h"
 #include "mozilla/Sprintf.h"
 #include "mozilla/FilePreferences.h"
+#include "prtime.h"
 
-#include <sys/types.h>
+#include <sys/fcntl.h>
+#include <sys/select.h>
 #include <sys/stat.h>
+#include <sys/time.h>
+#include <sys/types.h>
 #include <unistd.h>
 #include <fcntl.h>
 #include <errno.h>
@@ -1073,68 +1077,92 @@ nsLocalFile::Remove(bool aRecursive) {
   return NSRESULT_FOR_RETURN(rmdir(mPath.get()));
 }
 
-NS_IMETHODIMP
-nsLocalFile::GetLastModifiedTime(PRTime* aLastModTime) {
+nsresult nsLocalFile::GetLastModifiedTimeImpl(PRTime* aLastModTime,
+                                              bool aFollowLinks) {
   CHECK_mPath();
   if (NS_WARN_IF(!aLastModTime)) {
     return NS_ERROR_INVALID_ARG;
   }
 
-  PRFileInfo64 info;
-  if (PR_GetFileInfo64(mPath.get(), &info) != PR_SUCCESS) {
+  using StatFn = int (*)(const char*, struct STAT*);
+  StatFn statFn = aFollowLinks ? &STAT : &LSTAT;
+
+  struct STAT fileStats {};
+  if (statFn(mPath.get(), &fileStats) < 0) {
     return NSRESULT_FOR_ERRNO();
   }
-  PRTime modTime = info.modifyTime;
-  if (modTime == 0) {
-    *aLastModTime = 0;
-  } else {
-    *aLastModTime = modTime / PR_USEC_PER_MSEC;
-  }
+
+  int64_t modSec = 0;
+  int64_t modNSec = 0;
+#if (defined(__APPLE__) && defined(__MACH__))
+  modSec = fileStats.st_mtimespec.tv_sec;
+  modNSec = fileStats.st_mtimespec.tv_nsec;
+#else
+  modSec = fileStats.st_mtim.tv_sec;
+  modNSec = fileStats.st_mtim.tv_nsec;
+#endif
+  *aLastModTime =
+      PRTime(modSec * PR_MSEC_PER_SEC) + PRTime(modNSec / PR_NSEC_PER_MSEC);
 
   return NS_OK;
 }
 
-NS_IMETHODIMP
-nsLocalFile::SetLastModifiedTime(PRTime aLastModTime) {
+nsresult nsLocalFile::SetLastModifiedTimeImpl(PRTime aLastModTime,
+                                              bool aFollowLinks) {
   CHECK_mPath();
 
+  using UtimesFn = int (*)(const char*, const timeval*);
+  UtimesFn utimesFn = &utimes;
+
+#if HAVE_LUTIMES
+  if (!aFollowLinks) {
+    utimesFn = &lutimes;
+  }
+#endif
+
   int result;
   if (aLastModTime != 0) {
     ENSURE_STAT_CACHE();
-    struct utimbuf ut;
-    ut.actime = mCachedStat.st_atime;
+    timeval access{};
+#if (defined(__APPLE__) && defined(__MACH__))
+    access.tv_sec = mCachedStat.st_atimespec.tv_sec;
+    access.tv_usec = mCachedStat.st_atimespec.tv_nsec / 1000;
+#else
+    access.tv_sec = mCachedStat.st_atim.tv_sec;
+    access.tv_usec = mCachedStat.st_atim.tv_nsec / 1000;
+#endif
+    timeval modification{};
+    modification.tv_sec = aLastModTime / PR_MSEC_PER_SEC;
+    modification.tv_usec = (aLastModTime % PR_MSEC_PER_SEC) * PR_USEC_PER_MSEC;
 
-    // convert milliseconds to seconds since the unix epoch
-    ut.modtime = (time_t)(aLastModTime / PR_MSEC_PER_SEC);
-    result = utime(mPath.get(), &ut);
+    timeval times[2];
+    times[0] = access;
+    times[1] = modification;
+    result = utimesFn(mPath.get(), times);
   } else {
-    result = utime(mPath.get(), nullptr);
+    result = utimesFn(mPath.get(), nullptr);
   }
   return NSRESULT_FOR_RETURN(result);
 }
 
 NS_IMETHODIMP
-nsLocalFile::GetLastModifiedTimeOfLink(PRTime* aLastModTimeOfLink) {
-  CHECK_mPath();
-  if (NS_WARN_IF(!aLastModTimeOfLink)) {
-    return NS_ERROR_INVALID_ARG;
-  }
-
-  struct STAT sbuf;
-  if (LSTAT(mPath.get(), &sbuf) == -1) {
-    return NSRESULT_FOR_ERRNO();
-  }
-  *aLastModTimeOfLink = PRTime(sbuf.st_mtime) * PR_MSEC_PER_SEC;
-
-  return NS_OK;
+nsLocalFile::GetLastModifiedTime(PRTime* aLastModTime) {
+  return GetLastModifiedTimeImpl(aLastModTime, /* follow links? */ true);
+}
+
+NS_IMETHODIMP
+nsLocalFile::SetLastModifiedTime(PRTime aLastModTime) {
+  return SetLastModifiedTimeImpl(aLastModTime, /* follow links ? */ true);
+}
+
+NS_IMETHODIMP
+nsLocalFile::GetLastModifiedTimeOfLink(PRTime* aLastModTimeOfLink) {
+  return GetLastModifiedTimeImpl(aLastModTimeOfLink, /* follow link? */ false);
 }
 
-/*
- * utime(2) may or may not dereference symlinks, joy.
- */
 NS_IMETHODIMP
 nsLocalFile::SetLastModifiedTimeOfLink(PRTime aLastModTimeOfLink) {
-  return SetLastModifiedTime(aLastModTimeOfLink);
+  return SetLastModifiedTimeImpl(aLastModTimeOfLink, /* follow links? */ false);
 }
 
 /*

xpcom/io/nsLocalFileUnix.h

@@ -122,6 +122,9 @@ class nsLocalFile final
 
   nsresult CreateAndKeepOpen(uint32_t aType, int aFlags, uint32_t aPermissions,
                              PRFileDesc** aResult);
+
+  nsresult SetLastModifiedTimeImpl(PRTime aLastModTime, bool aFollowLinks);
+  nsresult GetLastModifiedTimeImpl(PRTime* aLastModTime, bool aFollowLinks);
 };
 
 #endif /* _nsLocalFileUNIX_H_ */