Re: [PATCH] Fix overwriting files with fs::copy_file on windows

[Jonathan Wakely <jwakely@redhat.com>]

On Sun, 24 Mar 2024 at 21:34, Björn Schäpers <gcc@hazardy.de> wrote:
>
> From: Björn Schäpers <bjoern@hazardy.de>
>
> This fixes i.e. https://github.com/msys2/MSYS2-packages/issues/1937
> I don't know if I picked the right way to do it.
>
> When acceptable I think the declaration should be moved into
> ops-common.h, since then we could use stat_type and also use that in the
> commonly used function.
>
> Manually tested on i686-w64-mingw32.
>
> -- >8 --
> libstdc++: Fix overwriting files on windows
>
> The inodes have no meaning on windows, thus all files have an inode of
> 0. Use a differenz approach to identify equivalent files. As a result
> std::filesystem::copy_file did not honor
> copy_options::overwrite_existing. Factored the method out of
> std::filesystem::equivalent.
>
> libstdc++-v3/Changelog:
>
>         * include/bits/fs_ops.h: Add declaration of
>           __detail::equivalent_win32.
>         * src/c++17/fs_ops.cc (__detail::equivalent_win32): Implement it
>         (fs::equivalent): Use __detail::equivalent_win32, factored the
>         old test out.
>         * src/filesystem/ops-common.h (_GLIBCXX_FILESYSTEM_IS_WINDOWS):
>           Use the function.
>
> Signed-off-by: Björn Schäpers <bjoern@hazardy.de>
> ---
>  libstdc++-v3/include/bits/fs_ops.h       |  8 +++
>  libstdc++-v3/src/c++17/fs_ops.cc         | 79 +++++++++++++-----------
>  libstdc++-v3/src/filesystem/ops-common.h | 10 ++-
>  3 files changed, 60 insertions(+), 37 deletions(-)
>
> diff --git a/libstdc++-v3/include/bits/fs_ops.h b/libstdc++-v3/include/bits/fs_ops.h
> index 90650c47b46..d10b78a4bdd 100644
> --- a/libstdc++-v3/include/bits/fs_ops.h
> +++ b/libstdc++-v3/include/bits/fs_ops.h
> @@ -40,6 +40,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>
>  namespace filesystem
>  {
> +#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
> +namespace __detail
> +{
> +  bool
> +  equivalent_win32(const wchar_t* p1, const wchar_t* p2, error_code& ec);

I don't think we want this declared in the public header, it should be
internal to the library.

Can it just be declared in ops-common.h instead?


> +} // namespace __detail
> +#endif //_GLIBCXX_FILESYSTEM_IS_WINDOWS
> +
>    /** @addtogroup filesystem
>     *  @{
>     */
> diff --git a/libstdc++-v3/src/c++17/fs_ops.cc b/libstdc++-v3/src/c++17/fs_ops.cc
> index 61df19753ef..3cc87d45237 100644
> --- a/libstdc++-v3/src/c++17/fs_ops.cc
> +++ b/libstdc++-v3/src/c++17/fs_ops.cc
> @@ -67,6 +67,49 @@
>  namespace fs = std::filesystem;
>  namespace posix = std::filesystem::__gnu_posix;
>
> +#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
> +bool
> +fs::__detail::equivalent_win32(const wchar_t* p1, const wchar_t* p2,
> +                              error_code& ec)
> +{
> +  struct auto_handle {
> +    explicit auto_handle(const path& p_)
> +    : handle(CreateFileW(p_.c_str(), 0,
> +       FILE_SHARE_DELETE | FILE_SHARE_READ | FILE_SHARE_WRITE,
> +       0, OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, 0))
> +    { }
> +
> +    ~auto_handle()
> +    { if (*this) CloseHandle(handle); }
> +
> +    explicit operator bool() const
> +    { return handle != INVALID_HANDLE_VALUE; }
> +
> +    bool get_info()
> +    { return GetFileInformationByHandle(handle, &info); }
> +
> +    HANDLE handle;
> +    BY_HANDLE_FILE_INFORMATION info;
> +  };
> +  auto_handle h1(p1);

This creates a new filesystem::path, just to call c_str() on it
immediately. The auto_handle ctor should be changed to just take const
wchar_t* so we don't need to allocate and parse new path objects.

> +  auto_handle h2(p2);
> +  if (!h1 || !h2)
> +    {
> +      if (!h1 && !h2)
> +       ec = __last_system_error();
> +      return false;
> +    }
> +  if (!h1.get_info() || !h2.get_info())
> +    {
> +      ec = __last_system_error();
> +      return false;
> +    }
> +  return h1.info.dwVolumeSerialNumber == h2.info.dwVolumeSerialNumber
> +    && h1.info.nFileIndexHigh == h2.info.nFileIndexHigh
> +    && h1.info.nFileIndexLow == h2.info.nFileIndexLow;
> +}
> +#endif //_GLIBCXX_FILESYSTEM_IS_WINDOWS
> +
>  fs::path
>  fs::absolute(const path& p)
>  {
> @@ -858,41 +901,7 @@ fs::equivalent(const path& p1, const path& p2, error_code& ec) noexcept
>        if (st1.st_mode != st2.st_mode || st1.st_dev != st2.st_dev)
>         return false;
>
> -      struct auto_handle {
> -       explicit auto_handle(const path& p_)
> -       : handle(CreateFileW(p_.c_str(), 0,
> -             FILE_SHARE_DELETE | FILE_SHARE_READ | FILE_SHARE_WRITE,
> -             0, OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, 0))
> -       { }
> -
> -       ~auto_handle()
> -       { if (*this) CloseHandle(handle); }
> -
> -       explicit operator bool() const
> -       { return handle != INVALID_HANDLE_VALUE; }
> -
> -       bool get_info()
> -       { return GetFileInformationByHandle(handle, &info); }
> -
> -       HANDLE handle;
> -       BY_HANDLE_FILE_INFORMATION info;
> -      };
> -      auto_handle h1(p1);
> -      auto_handle h2(p2);
> -      if (!h1 || !h2)
> -       {
> -         if (!h1 && !h2)
> -           ec = __last_system_error();
> -         return false;
> -       }
> -      if (!h1.get_info() || !h2.get_info())
> -       {
> -         ec = __last_system_error();
> -         return false;
> -       }
> -      return h1.info.dwVolumeSerialNumber == h2.info.dwVolumeSerialNumber
> -       && h1.info.nFileIndexHigh == h2.info.nFileIndexHigh
> -       && h1.info.nFileIndexLow == h2.info.nFileIndexLow;
> +      return __detail::equivalent_win32(p1.c_str(), p2.c_str(), ec);
>  #else
>        return st1.st_dev == st2.st_dev && st1.st_ino == st2.st_ino;
>  #endif
> diff --git a/libstdc++-v3/src/filesystem/ops-common.h b/libstdc++-v3/src/filesystem/ops-common.h
> index d917fddbeb1..7e67286bd01 100644
> --- a/libstdc++-v3/src/filesystem/ops-common.h
> +++ b/libstdc++-v3/src/filesystem/ops-common.h
> @@ -489,8 +489,14 @@ _GLIBCXX_BEGIN_NAMESPACE_FILESYSTEM
>             return false;
>           }
>
> -       if (to_st->st_dev == from_st->st_dev
> -           && to_st->st_ino == from_st->st_ino)
> +#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
> +       // st_ino is not set, so can't be used to distinguish files
> +       std::error_code not_used;
> +       if (st1.st_mode != st2.st_mode || st1.st_dev != st2.st_dev ||
> +           fs::__detail::equivalent_win32(from, to, not_used))
> +#else
> +       if (st1.st_dev != st2.st_dev || st1.st_ino != st2.st_ino)
> +#endif
>           {
>             ec = std::make_error_code(std::errc::file_exists);
>             return false;
> --
> 2.44.0
>