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 <[e-mail]>
Cc: Anton Altaparmakov <[e-mail]>
Cc: Al Viro <[e-mail]>
Cc: Christoph Hellwig <[e-mail]>
Cc: Vyacheslav Dubeyko <[e-mail]>
Cc: Hin-Tak Leung <[e-mail]>
Cc: Kyle Laracey <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/hfsplus/bnode.c

···
 		if (test_bit(HFS_BNODE_DELETED, &node->flags)) {
 			hfs_bnode_unhash(node);
 			spin_unlock(&tree->hash_lock);
-			hfs_bnode_clear(node, 0,
-				PAGE_CACHE_SIZE * tree->pages_per_bnode);
+			if (hfs_bnode_need_zeroout(tree))
+				hfs_bnode_clear(node, 0, tree->node_size);
 			hfs_bmap_free(node);
 			hfs_bnode_free(node);
 			return;
···
 	}
 }
 
+/*
+ * Unused nodes have to be zeroed if this is the catalog tree and
+ * a corresponding flag in the volume header is set.
+ */
+bool hfs_bnode_need_zeroout(struct hfs_btree *tree)
+{
+	struct super_block *sb = tree->inode->i_sb;
+	struct hfsplus_sb_info *sbi = HFSPLUS_SB(sb);
+	const u32 volume_attr = be32_to_cpu(sbi->s_vhdr->attributes);
+
+	return tree->cnid == HFSPLUS_CAT_CNID &&
+		volume_attr & HFSPLUS_VOL_UNUSED_NODE_FIX;
+}

fs/hfsplus/btree.c

···
 		u32 count;
 		int res;
 
-		res = hfsplus_file_extend(inode);
+		res = hfsplus_file_extend(inode, hfs_bnode_need_zeroout(tree));
 		if (res)
 			return ERR_PTR(res);
 		hip->phys_size = inode->i_size =

fs/hfsplus/extents.c

···
 		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;
 		}
···
 	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);
···
 			res = -ENOSPC;
 			goto out;
 		}
+	}
+
+	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);

fs/hfsplus/hfsplus_fs.h

···
 struct hfs_bnode *hfs_bnode_create(struct hfs_btree *, u32);
 void hfs_bnode_get(struct hfs_bnode *);
 void hfs_bnode_put(struct hfs_bnode *);
+bool hfs_bnode_need_zeroout(struct hfs_btree *);
 
 /* brec.c */
 u16 hfs_brec_lenoff(struct hfs_bnode *, u16, u16 *);
···
 int hfsplus_get_block(struct inode *, sector_t, struct buffer_head *, int);
 int hfsplus_free_fork(struct super_block *, u32,
 		struct hfsplus_fork_raw *, int);
-int hfsplus_file_extend(struct inode *);
+int hfsplus_file_extend(struct inode *, bool zeroout);
 void hfsplus_file_truncate(struct inode *);
 
 /* inode.c */

fs/hfsplus/hfsplus_raw.h

···
 #define HFSPLUS_VOL_NODEID_REUSED	(1 << 12)
 #define HFSPLUS_VOL_JOURNALED		(1 << 13)
 #define HFSPLUS_VOL_SOFTLOCK		(1 << 15)
+#define HFSPLUS_VOL_UNUSED_NODE_FIX	(1 << 31)
 
 /* HFS+ BTree node descriptor */
 struct hfs_bnode_desc {

fs/hfsplus/xattr.c

···
 	}
 
 	while (hip->alloc_blocks < hip->clump_blocks) {
-		err = hfsplus_file_extend(attr_file);
+		err = hfsplus_file_extend(attr_file, false);
 		if (unlikely(err)) {
 			pr_err("failed to extend attributes file\n");
 			goto end_attr_file_creation;