$ make KERNELSRC=/usr/src/linux-source-2.6.22 module
Building module for a 2.6 kernel
make[1]: Entering directory `/home/ruben/openswan-2.5.16'
make[2]: Entering directory `/home/ruben/openswan-2.5.16'
make[2]: `/home/ruben/openswan-2.5.16/modobj26/Makefile' is up to date.
make[2]: Leaving directory `/home/ruben/openswan-2.5.16'
make -C /usr/src/linux-source-2.6.22  BUILDDIR=/home/ruben/openswan-2.5.16/modobj26 SUBDIRS=/home/ruben/openswan-2.5.16/modobj26 MODULE_DEF_INCLUDE=/home/ruben/openswan-2.5.16/packaging/linus/config-all.h MODULE_DEFCONFIG=/home/ruben/openswan-2.5.16/linux/net/ipsec/defconfig  MODULE_EXTRA_INCLUDE= ARCH=x86_64 modules
make[2]: Entering directory `/usr/src/linux-source-2.6.22'

  WARNING: Symbol version dump /usr/src/linux-source-2.6.22/Module.symvers
           is missing; modules will have no dependencies and modversions.

  CC [M]  /home/ruben/openswan-2.5.16/modobj26/ipsec_tunnel.o
/home/ruben/openswan-2.5.16/modobj26/ipsec_tunnel.c: In function ‘ipsec_xmit_state_cache_init’:
/home/ruben/openswan-2.5.16/modobj26/ipsec_tunnel.c:1895: error: invalid application of ‘sizeof’ to incomplete type ‘struct ipsec_ixs’
/home/ruben/openswan-2.5.16/modobj26/ipsec_tunnel.c:1895: error: invalid application of ‘__alignof__’ to incomplete type ‘struct ipsec_ixs’
/home/ruben/openswan-2.5.16/modobj26/ipsec_tunnel.c:1888: warning: unused variable ‘ipsec_ixs’
make[3]: *** [/home/ruben/openswan-2.5.16/modobj26/ipsec_tunnel.o] Error 1
make[2]: *** [_module_/home/ruben/openswan-2.5.16/modobj26] Error 2
make[2]: Leaving directory `/usr/src/linux-source-2.6.22'
make[1]: *** [module26] Error 2
make[1]: Leaving directory `/home/ruben/openswan-2.5.16'
make: *** [module] Error 2