This patch by Dimitri Puzin submitted through kernel Bugzilla #5514
fixes the following issue:

Cannot build XFS filesystem support as module with quota support. It
works only when the XFS filesystem support is compiled into the kernel.
Menuconfig prevents from setting CONFIG_XFS_FS=m and CONFIG_XFS_QUOTA=y.

How to reproduce: configure the XFS filesystem with quota support as
module. The resulting kernel won't have quota support compiled into
xfs.ko.

Fix: Changing the fs/xfs/Kconfig file from tristate to bool lets you
configure the quota support to be compiled into the XFS module. The
Makefile-linux-2.6 checks only for CONFIG_XFS_QUOTA=y.
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Nathan Scott <nathans@sgi.com>
Signed-off-by: Chris Wright <chrisw@osdl.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>