hfsplus: fix "unused node is not erased" error

Zero newly allocated extents in the catalog tree if volume attributes
tell us to.  Not doing so we risk getting the "unused node is not
erased" error.  See kHFSUnusedNodeFix flag in Apple's source code for
reference.

There was a previous commit clearing the node when it is freed: commit
899bed05e9f6 ("hfsplus: fix issue with unzeroed unused b-tree nodes").
But it did not handle newly allocated extents (this patch fixes it).
And it zeroed nodes in all trees unconditionally which is an overkill.

This patch adds a condition and also switches to 'tree->node_size' as a
simpler method of getting the length to zero.

Signed-off-by: Sergei Antonov <saproj@gmail.com>
Cc: Anton Altaparmakov <aia21@cam.ac.uk>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Vyacheslav Dubeyko <slava@dubeyko.com>
Cc: Hin-Tak Leung <htl10@users.sourceforge.net>
Cc: Kyle Laracey <kalaracey@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/hfsplus/extents.c b/fs/hfsplus/extents.c
index a7aafb35..a09fcb6 100644
--- a/fs/hfsplus/extents.c
+++ b/fs/hfsplus/extents.c
@@ -235,7 +235,7 @@
 		if (iblock > hip->fs_blocks || !create)
 			return -EIO;
 		if (ablock >= hip->alloc_blocks) {
-			res = hfsplus_file_extend(inode);
+			res = hfsplus_file_extend(inode, false);
 			if (res)
 				return res;
 		}
@@ -425,7 +425,7 @@
 	return res;
 }
 
-int hfsplus_file_extend(struct inode *inode)
+int hfsplus_file_extend(struct inode *inode, bool zeroout)
 {
 	struct super_block *sb = inode->i_sb;
 	struct hfsplus_sb_info *sbi = HFSPLUS_SB(sb);
@@ -463,6 +463,12 @@
 		}
 	}
 
+	if (zeroout) {
+		res = sb_issue_zeroout(sb, start, len, GFP_NOFS);
+		if (res)
+			goto out;
+	}
+
 	hfs_dbg(EXTENT, "extend %lu: %u,%u\n", inode->i_ino, start, len);
 
 	if (hip->alloc_blocks <= hip->first_blocks) {