Linux 3.13 compat: Handle __must_check bdi_setup_and_register

torvalds/linux@8077c0d983ab276ec5f2700df56a64d671781905 added a
__must_check to the bdi_setup_and_register(), which caused our autotools
check to break. zfsonlinux/zfs@729210564a5325e190fc4fba22bf17bacf957ace
was intended to correct that, but it depended on -Wno-unused-result,
which is unrecognized in older GCC versions. That commit has been
reverted in favor of a solution that does not require
-Wno-unused-result.

Signed-off-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #2102
Closes #2135

diff --git a/config/kernel-bdi-setup-and-register.m4 b/config/kernel-bdi-setup-and-register.m4
index 4196091e91bea70a89ae63201715f075e786b46e..6369409b8b39a6475b7c2ecc436094952f0489d9 100644 (file)
--- a/config/kernel-bdi-setup-and-register.m4
+++ b/config/kernel-bdi-setup-and-register.m4
@@ -1,6 +1,6 @@
 dnl #
 dnl # 2.6.34 API change
-dnl # The bdi_setup_and_register() helper function is avilable and
+dnl # The bdi_setup_and_register() helper function is avaliable and
 dnl # exported by the kernel.  This is a trivial helper function but
 dnl # using it significantly simplifies the code surrounding setting
 dnl # up and tearing down the bdi structure.
@@ -10,7 +10,8 @@ AC_DEFUN([ZFS_AC_KERNEL_BDI_SETUP_AND_REGISTER],
        ZFS_LINUX_TRY_COMPILE_SYMBOL([
                #include <linux/backing-dev.h>
        ], [
-               bdi_setup_and_register(NULL, NULL, 0);
+               int r = bdi_setup_and_register(NULL, NULL, 0);
+               r = *(&r);
        ], [bdi_setup_and_register], [mm/backing-dev.c], [
                AC_MSG_RESULT(yes)
                AC_DEFINE(HAVE_BDI_SETUP_AND_REGISTER, 1,