Add some functions to fd.c for the convenience of extensions.

For example, if you want to perform an ioctl() on a file descriptor
opened through the fd.c routines, there's no way to do that without
being able to get at the underlying fd.

KaiGai Kohei

src/backend/storage/file/fd.c

@@ -1577,6 +1577,40 @@ FilePathName(File file)
 	return VfdCache[file].fileName;
 }
 
+/*
+ * Return the raw file descriptor of an opened file.
+ *
+ * The returned file descriptor will be valid until the file is closed, but
+ * there are a lot of things that can make that happen.  So the caller should
+ * be careful not to do much of anything else before it finishes using the
+ * returned file descriptor.
+ */
+int
+FileGetRawDesc(File file)
+{
+	Assert(FileIsValid(file));
+	return VfdCache[file].fd;
+}
+
+/*
+ * FileGetRawFlags - returns the file flags on open(2)
+ */
+int
+FileGetRawFlags(File file)
+{
+	Assert(FileIsValid(file));
+	return VfdCache[file].fileFlags;
+}
+
+/*
+ * FileGetRawMode - returns the mode bitmask passed to open(2)
+ */
+int
+FileGetRawMode(File file)
+{
+	Assert(FileIsValid(file));
+	return VfdCache[file].fileMode;
+}
 
 /*
  * Make room for another allocatedDescs[] array entry if needed and possible.

src/include/storage/fd.h

@@ -75,6 +75,9 @@ extern int	FileSync(File file);
 extern off_t FileSeek(File file, off_t offset, int whence);
 extern int	FileTruncate(File file, off_t offset);
 extern char *FilePathName(File file);
+extern int	FileGetRawDesc(File file);
+extern int  FileGetRawFlags(File file);
+extern int	FileGetRawMode(File file);
 
 /* Operations that allow use of regular stdio --- USE WITH CAUTION */
 extern FILE *AllocateFile(const char *name, const char *mode);