system/FileDescriptor: add method IsRegularFile()

src/system/FileDescriptor.cxx

@@ -60,6 +60,13 @@ FileDescriptor::IsValid() const noexcept
 }
 
 bool
+FileDescriptor::IsRegularFile() const noexcept
+{
+	struct stat st;
+	return IsDefined() && fstat(fd, &st) == 0 && S_ISREG(st.st_mode);
+}
+
+bool
 FileDescriptor::IsPipe() const noexcept
 {
 	struct stat st;

src/system/FileDescriptor.hxx

@@ -79,6 +79,12 @@ public:
 	bool IsValid() const noexcept;
 
 	/**
+	 * Ask the kernel whether this is a regular file.
+	 */
+	gcc_pure
+	bool IsRegularFile() const noexcept;
+
+	/**
 	 * Ask the kernel whether this is a pipe.
 	 */
 	gcc_pure