From b06355f0fe04a62d08238438654ec453e05304ba Mon Sep 17 00:00:00 2001
From: Christoph Hellwig <hch@lst.de>
Date: Mon, 10 Sep 2007 20:02:32 -0400
Subject: [PATCH] Btrfs: [PATCH] extent_map: make the writepage_io hook
 optional

The writepage_io is not mandatory, e.g. my port of xfs to the extent_map
code does not have one for now.  So handle a NULL pointer gracefully
here.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
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