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

["Björn Schäpers" <gcc@hazardy.de>]

Am 24.03.2024 um 22:34 schrieb Björn Schäpers:
> 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);
> +} // 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);
> +  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;

A friendly ping.