On Mon, Jun 18 2018, Christoph Hellwig wrote:

> On Mon, Jun 18, 2018 at 02:55:20PM +1000, NeilBrown wrote:
>> This set of patches makes it possible to build a module from
>> code in multiple directories without needing to list files from one
>> directory in the Makefile of another directory.
>> 
>> The code was developed for lustre (which is now out-of-tree :-( ) but
>> can be useful elsewhere, such as for xfs and btrfs and others.
>> 
>> In fs/xfs/Makefile the section:
>> 
>> xfs-y				+= $(addprefix libxfs/, \
>> 				   xfs_ag.o \
>> 				   xfs_alloc.o \
>> 				.....
>> 
>> could become
>> 
>> xfs-y += libxfs/
>> 
>> and then in fs/xfs/libxfs/Makefile we would have
>> 
>> modobj-$(CONFIG_XFS_FS) += xfs_ag.o \
>> 			   xfs_alloc.o \
>> 			   .....
>> 
>> A similar process could move filenames for scrub/* from the
>> fs/xfs/Makefile to fs/xfs/scrub/Makefile
>
> How about you actually convert it as an example?

Sure ... found a bug while testing it.  Thanks :-)

From ac7953b4ba6d9a2a69dab84dd772aafca38d8377 Mon Sep 17 00:00:00 2001
From: NeilBrown <neilb@suse.com>
Date: Tue, 19 Jun 2018 13:59:16 +1000
Subject: [PATCH] kbuild/xfs: example modobj-m conversion

This is a demonstration patch to show how
xfs can be changed to make use of the proposed modobj-m=
functionality, should the xfs developers want that.

Signed-off-by: NeilBrown <neilb@suse.com>
---
 fs/xfs/Makefile        | 78 ++------------------------------------------------
 fs/xfs/libxfs/Makefile | 43 ++++++++++++++++++++++++++++
 fs/xfs/scrub/Makefile  | 29 +++++++++++++++++++
 3 files changed, 74 insertions(+), 76 deletions(-)
 create mode 100644 fs/xfs/libxfs/Makefile
 create mode 100644 fs/xfs/scrub/Makefile

diff --git a/fs/xfs/Makefile b/fs/xfs/Makefile
index 2f3f75a7f180..0ba854045fe9 100644
--- a/fs/xfs/Makefile
+++ b/fs/xfs/Makefile
@@ -15,47 +15,7 @@ obj-$(CONFIG_XFS_FS)		+= xfs.o
 xfs-y				+= xfs_trace.o
 
 # build the libxfs code first
-xfs-y				+= $(addprefix libxfs/, \
-				   xfs_ag.o \
-				   xfs_alloc.o \
-				   xfs_alloc_btree.o \
-				   xfs_attr.o \
-				   xfs_attr_leaf.o \
-				   xfs_attr_remote.o \
-				   xfs_bit.o \
-				   xfs_bmap.o \
-				   xfs_bmap_btree.o \
-				   xfs_btree.o \
-				   xfs_da_btree.o \
-				   xfs_da_format.o \
-				   xfs_defer.o \
-				   xfs_dir2.o \
-				   xfs_dir2_block.o \
-				   xfs_dir2_data.o \
-				   xfs_dir2_leaf.o \
-				   xfs_dir2_node.o \
-				   xfs_dir2_sf.o \
-				   xfs_dquot_buf.o \
-				   xfs_ialloc.o \
-				   xfs_ialloc_btree.o \
-				   xfs_iext_tree.o \
-				   xfs_inode_fork.o \
-				   xfs_inode_buf.o \
-				   xfs_log_rlimit.o \
-				   xfs_ag_resv.o \
-				   xfs_rmap.o \
-				   xfs_rmap_btree.o \
-				   xfs_refcount.o \
-				   xfs_refcount_btree.o \
-				   xfs_sb.o \
-				   xfs_symlink_remote.o \
-				   xfs_trans_resv.o \
-				   xfs_types.o \
-				   )
-# xfs_rtbitmap is shared with libxfs
-xfs-$(CONFIG_XFS_RT)		+= $(addprefix libxfs/, \
-				   xfs_rtbitmap.o \
-				   )
+xfs-y				+= libxfs/
 
 # highlevel code
 xfs-y				+= xfs_aops.o \
@@ -127,38 +87,4 @@ xfs-$(CONFIG_SYSCTL)		+= xfs_sysctl.o
 xfs-$(CONFIG_COMPAT)		+= xfs_ioctl32.o
 xfs-$(CONFIG_EXPORTFS_BLOCK_OPS)	+= xfs_pnfs.o
 
-# online scrub/repair
-ifeq ($(CONFIG_XFS_ONLINE_SCRUB),y)
-
-# Tracepoints like to blow up, so build that before everything else
-
-xfs-y				+= $(addprefix scrub/, \
-				   trace.o \
-				   agheader.o \
-				   alloc.o \
-				   attr.o \
-				   bmap.o \
-				   btree.o \
-				   common.o \
-				   dabtree.o \
-				   dir.o \
-				   ialloc.o \
-				   inode.o \
-				   parent.o \
-				   refcount.o \
-				   rmap.o \
-				   scrub.o \
-				   symlink.o \
-				   )
-
-xfs-$(CONFIG_XFS_RT)		+= scrub/rtbitmap.o
-xfs-$(CONFIG_XFS_QUOTA)		+= scrub/quota.o
-
-# online repair
-ifeq ($(CONFIG_XFS_ONLINE_REPAIR),y)
-xfs-y				+= $(addprefix scrub/, \
-				   agheader_repair.o \
-				   repair.o \
-				   )
-endif
-endif
+xfs-$(CONFIG_XFS_ONLINE_SCRUB)	+= scrub/
diff --git a/fs/xfs/libxfs/Makefile b/fs/xfs/libxfs/Makefile
new file mode 100644
index 000000000000..9b90c289bdda
--- /dev/null
+++ b/fs/xfs/libxfs/Makefile
@@ -0,0 +1,43 @@
+# SPDX-License-Identifier: GPL-2.0
+
+ccflags-y += -I$(src)/..
+
+# xfs_rtbitmap is shared with libxfs
+xobj-$(CONFIG_XFS_RT)		+= xfs_rtbitmap.o
+
+modobj-$(CONFIG_XFS_FS) +=	   xfs_ag.o \
+				   xfs_alloc.o \
+				   xfs_alloc_btree.o \
+				   xfs_attr.o \
+				   xfs_attr_leaf.o \
+				   xfs_attr_remote.o \
+				   xfs_bit.o \
+				   xfs_bmap.o \
+				   xfs_bmap_btree.o \
+				   xfs_btree.o \
+				   xfs_da_btree.o \
+				   xfs_da_format.o \
+				   xfs_defer.o \
+				   xfs_dir2.o \
+				   xfs_dir2_block.o \
+				   xfs_dir2_data.o \
+				   xfs_dir2_leaf.o \
+				   xfs_dir2_node.o \
+				   xfs_dir2_sf.o \
+				   xfs_dquot_buf.o \
+				   xfs_ialloc.o \
+				   xfs_ialloc_btree.o \
+				   xfs_iext_tree.o \
+				   xfs_inode_fork.o \
+				   xfs_inode_buf.o \
+				   xfs_log_rlimit.o \
+				   xfs_ag_resv.o \
+				   xfs_rmap.o \
+				   xfs_rmap_btree.o \
+				   xfs_refcount.o \
+				   xfs_refcount_btree.o \
+				   xfs_sb.o \
+				   xfs_symlink_remote.o \
+				   xfs_trans_resv.o \
+				   xfs_types.o \
+				   $(xobj-y)
diff --git a/fs/xfs/scrub/Makefile b/fs/xfs/scrub/Makefile
new file mode 100644
index 000000000000..f91818a0e6ee
--- /dev/null
+++ b/fs/xfs/scrub/Makefile
@@ -0,0 +1,29 @@
+# SPDX-License-Identifier: GPL-2.0
+
+# Tracepoints like to blow up, so build that before everything else
+
+ccflags-y += -I$(src)/..
+ccflags-y += -I$(src)/../libxfs
+
+xobj-$(CONFIG_XFS_RT)		+= rtbitmap.o
+xobj-$(CONFIG_XFS_QUOTA)	+= quota.o
+xobj-$(CONFIG_XFS_ONLINE_REPAIR)+= agheader_repair.o \
+				   repair.o
+
+modobj-$(CONFIG_XFS_FS) +=	   trace.o \
+				   agheader.o \
+				   alloc.o \
+				   attr.o \
+				   bmap.o \
+				   btree.o \
+				   common.o \
+				   dabtree.o \
+				   dir.o \
+				   ialloc.o \
+				   inode.o \
+				   parent.o \
+				   refcount.o \
+				   rmap.o \
+				   scrub.o \
+				   symlink.o \
+				   $(xobj-y)
-- 
2.14.0.rc0.dirty