In C++17 the clock used for filesystem::file_time_type is unspecified,
allowing it to be chrono::system_clock. The C++2a draft requires it to
be a distinct type, with additional member functions to convert to/from
other clocks (either the system clock or UTC). In order to avoid an ABI
change later, this patch defines a new distinct type now, which will be
used for std::chrono::file_clock later.
* include/bits/fs_fwd.h (__file_clock): Define new clock.
(file_time_type): Redefine in terms of __file_clock.
* src/filesystem/ops-common.h (file_time): Add FIXME comment about
overflow.
* src/filesystem/std-ops.cc (is_set(perm_options, perm_options)): Give
internal linkage.
(internal_file_lock): New helper type for accessing __file_clock.
(do_copy_file): Use internal_file_lock to convert system time to
file_time_type.
(last_write_time(const path&, error_code&)): Likewise.
(last_write_time(const path&, file_time_type, error_code&)): Likewise.
Tested powerpc64-linux, committed to trunk.
commit c91a86730ed8df76325dd0649d8837e6feb24aab
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Sat Jan 5 12:52:40 2019 +0000
Define new filesystem::__file_clock type
In C++17 the clock used for filesystem::file_time_type is unspecified,
allowing it to be chrono::system_clock. The C++2a draft requires it to
be a distinct type, with additional member functions to convert to/from
other clocks (either the system clock or UTC). In order to avoid an ABI
change later, this patch defines a new distinct type now, which will be
used for std::chrono::file_clock later.
* include/bits/fs_fwd.h (__file_clock): Define new clock.
(file_time_type): Redefine in terms of __file_clock.
* src/filesystem/ops-common.h (file_time): Add FIXME comment about
overflow.
* src/filesystem/std-ops.cc (is_set(perm_options, perm_options)):
Give
internal linkage.
(internal_file_lock): New helper type for accessing __file_clock.
(do_copy_file): Use internal_file_lock to convert system time to
file_time_type.
(last_write_time(const path&, error_code&)): Likewise.
(last_write_time(const path&, file_time_type, error_code&)):
Likewise.
diff --git a/libstdc++-v3/include/bits/fs_fwd.h
b/libstdc++-v3/include/bits/fs_fwd.h
index 3bcf2dd650c..a0e3d73e2a3 100644
--- a/libstdc++-v3/include/bits/fs_fwd.h
+++ b/libstdc++-v3/include/bits/fs_fwd.h
@@ -294,7 +294,49 @@ _GLIBCXX_END_NAMESPACE_CXX11
operator^=(directory_options& __x, directory_options __y) noexcept
{ return __x = __x ^ __y; }
- using file_time_type = std::chrono::system_clock::time_point;
+ struct __file_clock
+ {
+ using duration = chrono::nanoseconds;
+ using rep = duration::rep;
+ using period = duration::period;
+ using time_point = chrono::time_point<__file_clock>;
+ static constexpr bool is_steady = false;
+
+ static time_point
+ now() noexcept
+ { return _S_from_sys(chrono::system_clock::now()); }
+
+ private:
+ using __sys_clock = chrono::system_clock;
+
+ // This clock's (unspecified) epoch is 2174-01-01 00:00:00 UTC.
+ // A signed 64-bit duration with nanosecond resolution gives roughly
+ // +/- 292 years, which covers the 1901-2446 date range for ext4.
+ static constexpr chrono::seconds _S_epoch_diff{6437664000};
+
+ protected:
+ // For internal use only
+ template<typename _Dur>
+ static
+ chrono::time_point<__file_clock, _Dur>
+ _S_from_sys(const chrono::time_point<__sys_clock, _Dur>& __t) noexcept
+ {
+ using __file_time = chrono::time_point<__file_clock, _Dur>;
+ return __file_time{__t.time_since_epoch()} - _S_epoch_diff;
+ }
+
+ // For internal use only
+ template<typename _Dur>
+ static
+ chrono::time_point<__sys_clock, _Dur>
+ _S_to_sys(const chrono::time_point<__file_clock, _Dur>& __t) noexcept
+ {
+ using __sys_time = chrono::time_point<__sys_clock, _Dur>;
+ return __sys_time{__t.time_since_epoch()} + _S_epoch_diff;
+ }
+ };
+
+ using file_time_type = __file_clock::time_point;
// operational functions
diff --git a/libstdc++-v3/src/filesystem/ops-common.h
b/libstdc++-v3/src/filesystem/ops-common.h
index dcd61cc26cd..1c0d650f444 100644
--- a/libstdc++-v3/src/filesystem/ops-common.h
+++ b/libstdc++-v3/src/filesystem/ops-common.h
@@ -158,6 +158,24 @@ namespace __gnu_posix
nanoseconds ns{};
#endif
+ // FIXME
+ // There are possible timespec values which will overflow
+ // chrono::system_clock::time_point but would not overflow
+ // __file_clock::time_point, due to its different epoch.
+ //
+ // By checking for overflow of the intermediate system_clock::duration
+ // type, we report an error for values which are actually representable
+ // in the file_time_type result type.
+ //
+ // Howard Hinnant's solution for this problem is to use
+ // duration<__int128>{s} + ns, which doesn't overflow.
+ // An alternative would be to do the epoch correction on s before
+ // the addition, and then go straight to file_time_type instead of
+ // going via chrono::system_clock::time_point.
+ //
+ // (This only applies to the C++17 Filesystem library, because for the
+ // Filesystem TS we don't have a distinct __file_clock, we just use the
+ // system clock for file timestamps).
if (s >= (nanoseconds::max().count() / 1e9))
{
ec = std::make_error_code(std::errc::value_too_large); // EOVERFLOW
diff --git a/libstdc++-v3/src/filesystem/std-ops.cc
b/libstdc++-v3/src/filesystem/std-ops.cc
index 26a7ad2a198..8c3ec1d9a9a 100644
--- a/libstdc++-v3/src/filesystem/std-ops.cc
+++ b/libstdc++-v3/src/filesystem/std-ops.cc
@@ -268,13 +268,32 @@ fs::copy(const path& from, const path& to, copy_options
options)
namespace std::filesystem
{
// Need this as there's no 'perm_options::none' enumerator.
- inline bool is_set(fs::perm_options obj, fs::perm_options bits)
+ static inline bool is_set(fs::perm_options obj, fs::perm_options bits)
{
return (obj & bits) != fs::perm_options{};
}
}
#ifdef _GLIBCXX_HAVE_SYS_STAT_H
+
+namespace
+{
+ struct internal_file_clock : fs::__file_clock
+ {
+ using __file_clock::_S_to_sys;
+ using __file_clock::_S_from_sys;
+
+ static fs::file_time_type
+ from_stat(const fs::stat_type& st, std::error_code& ec) noexcept
+ {
+ const auto sys_time = fs::file_time(st, ec);
+ if (sys_time == sys_time.min())
+ return fs::file_time_type::min();
+ return _S_from_sys(sys_time);
+ }
+ };
+}
+
#ifdef NEED_DO_COPY_FILE
bool
fs::do_copy_file(const path::value_type* from, const path::value_type* to,
@@ -348,10 +367,10 @@ fs::do_copy_file(const path::value_type* from, const
path::value_type* to,
}
else if (options.update)
{
- const auto from_mtime = file_time(*from_st, ec);
+ const auto from_mtime = internal_file_clock::from_stat(*from_st, ec);
if (ec)
return false;
- if ((from_mtime <= file_time(*to_st, ec)) || ec)
+ if ((from_mtime <= internal_file_clock::from_stat(*to_st, ec)) || ec)
return false;
}
else if (!options.overwrite)
@@ -1122,7 +1141,10 @@ fs::last_write_time(const path& p)
fs::file_time_type
fs::last_write_time(const path& p, error_code& ec) noexcept
{
- return do_stat(p, ec, [&ec](const auto& st) { return file_time(st, ec); },
+ return do_stat(p, ec,
+ [&ec](const auto& st) {
+ return internal_file_clock::from_stat(st, ec);
+ },
file_time_type::min());
}
@@ -1139,7 +1161,7 @@ void
fs::last_write_time(const path& p __attribute__((__unused__)),
file_time_type new_time, error_code& ec) noexcept
{
- auto d = new_time.time_since_epoch();
+ auto d = internal_file_clock::_S_to_sys(new_time).time_since_epoch();
auto s = chrono::duration_cast<chrono::seconds>(d);
#if _GLIBCXX_USE_UTIMENSAT
auto ns = chrono::duration_cast<chrono::nanoseconds>(d - s);
