Android: Provide futimes() implementation using utimensat()

base/os_compat_android.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/os_compat_android.h"
 
+#include <asm/unistd.h>
 #include <errno.h>
 #include <math.h>
 #include <sys/stat.h>
+#include <sys/syscall.h>
 #include <time64.h>
 
 #include "base/rand_util.h"
 #include "base/stringprintf.h"
 #include "base/strings/string_piece.h"
 
+extern "C" {
 // There is no futimes() avaiable in Bionic, so we provide our own
 // implementation until it is there.
-extern "C" {
-
 int futimes(int fd, const struct timeval tv[2]) {
-  const std::string fd_path = base::StringPrintf("/proc/self/fd/%d", fd);
-  return utimes(fd_path.c_str(), tv);
+  return syscall(__NR_utimensat, fd, NULL, tv, 0);

[Mark Mentovai, 2013/06/06 00:50:59]

utimensat can be used to implement futimens. The time argument is a timespec[2].
A timespec specifies seconds and nanoseconds.

futimes’ time argument is a timeval[2]. A timeval specifies seconds and
microseconds.

timeval and timespec are both the same width and have the same alignment, so you
may not have noticed the problem unless you actually looked at the fractional
second portion of the times set on files, but your implementation confuses
nanoseconds and microseconds.

[nilesh, 2013/06/06 01:57:36]

Thanks for catching this. I am now converting timeval to timespec.

I tried adding a test for this, but looks like the fractional value is ignored
on most filesystems. PlatformFile.TouchGetInfoPlatformFile says that "ext2/ext3
and HPS/HPS+ seem to have a timestamp granularity of 1s." and hence only checks
for the seconds value in tests.

Please take another look.

 }
 
 // Android has only timegm64() and no timegm().
 // We replicate the behaviour of timegm() when the result overflows time_t.
 time_t timegm(struct tm* const t) {
   // time_t is signed on Android.
   static const time_t kTimeMax = ~(1 << (sizeof(time_t) * CHAR_BIT - 1));
   static const time_t kTimeMin = (1 << (sizeof(time_t) * CHAR_BIT - 1));
   time64_t result = timegm64(t);
   if (result < kTimeMin || result > kTimeMax)
@@ skipping 113 matching lines @@
       // The directory doesn't exist, but an error occured
       return NULL;
     }
   }
 
   // We reached the max number of tries.
   return NULL;
 }
 
 }  // extern "C"