fs/affs: make export work with cold dcache

This adds get_parent function so that nfs client can still work after
cache drop (Tested on NFS v4 with echo 3 > /proc/sys/vm/drop_caches)

[[email protected]: fix return value check in affs_get_parent()]
  Link: http://lkml.kernel.org/r/[email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Fabian Frederick <[email protected]>
Signed-off-by: Wei Yongjun <[email protected]>
Suggested-by: Alexander Viro <[email protected]>
Cc: Al Viro <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

fs/affs/namei.c

@@ -447,6 +447,24 @@ done:
 	return retval;
 }
 
+static struct dentry *affs_get_parent(struct dentry *child)
+{
+	struct inode *parent;
+	struct buffer_head *bh;
+
+	bh = affs_bread(child->d_sb, d_inode(child)->i_ino);
+	if (!bh)
+		return ERR_PTR(-EIO);
+
+	parent = affs_iget(child->d_sb,
+			   be32_to_cpu(AFFS_TAIL(child->d_sb, bh)->parent));
+	brelse(bh);
+	if (IS_ERR(parent))
+		return ERR_CAST(parent);
+
+	return d_obtain_alias(parent);
+}
+
 static struct inode *affs_nfs_get_inode(struct super_block *sb, u64 ino,
 					u32 generation)
 {
@@ -484,6 +502,7 @@ static struct dentry *affs_fh_to_parent(struct super_block *sb, struct fid *fid,
 const struct export_operations affs_export_ops = {
 	.fh_to_dentry = affs_fh_to_dentry,
 	.fh_to_parent = affs_fh_to_parent,
+	.get_parent = affs_get_parent,
 };
 
 const struct dentry_operations affs_dentry_operations = {