fs/FileInfo: add fstat() wrapper

src/fs/FileInfo.cxx

@@ -8,6 +8,8 @@
 #ifdef _WIN32
 #include <windef.h> // for HWND (needed by winbase.h)
 #include <winbase.h> // for FILE_*_INFO
+#else
+#include "io/FileDescriptor.hxx"
 #endif
 
 FileInfo::FileInfo(Path path, bool follow_symlinks)
@@ -55,4 +57,12 @@ GetFileInfoByHandle(HANDLE handle, FileInfo &info) noexcept
 	return true;
 }
 
+#else
+
+FileInfo::FileInfo(FileDescriptor fd)
+{
+	if (fstat(fd.Get(), &st) < 0)
+		throw MakeErrno("Failed to access file");
+}
+
 #endif // _WIN32

src/fs/FileInfo.hxx

@@ -14,6 +14,8 @@
 #include <chrono>
 #include <cstdint>
 
+class FileDescriptor;
+
 class FileInfo {
 	friend bool GetFileInfo(Path path, FileInfo &info,
 				bool follow_symlinks) noexcept;
@@ -21,8 +23,6 @@ class FileInfo {
 	friend bool GetFileInfoByHandle(HANDLE handle, FileInfo &info) noexcept;
 #endif
 
-	friend class FileReader;
-
 #ifdef _WIN32
 	WIN32_FILE_ATTRIBUTE_DATA data;
 #else
@@ -36,6 +36,8 @@ public:
 
 #ifdef _WIN32
 	explicit FileInfo(HANDLE handle);
+#else
+	explicit FileInfo(FileDescriptor fd);
 #endif
 
 	constexpr bool IsRegular() const noexcept {

src/io/FileReader.cxx

@@ -73,12 +73,7 @@ FileReader::GetFileInfo() const
 {
 	assert(IsDefined());
 
-	FileInfo info;
-	const bool success = fstat(fd.Get(), &info.st) == 0;
-	if (!success)
-		throw MakeErrno("Failed to access file");
-
-	return info;
+	return FileInfo{fd};
 }
 
 std::size_t