[PATCH v4] arm: OABI compat: fix build when EPOLL is not enabled

[Randy Dunlap <rdunlap@infradead.org>]

When CONFIG_EPOLL is not set/enabled, sys_oabi-compat.c has build
errors. Fix these by surrounding them with ifdef CONFIG_EPOLL/endif
and providing stubs for the "EPOLL is not set" case.

../arch/arm/kernel/sys_oabi-compat.c: In function 'sys_oabi_epoll_ctl':
../arch/arm/kernel/sys_oabi-compat.c:257:6: error: implicit declaration of function 'ep_op_has_event' [-Werror=implicit-function-declaration]
  257 |  if (ep_op_has_event(op) &&
      |      ^~~~~~~~~~~~~~~
../arch/arm/kernel/sys_oabi-compat.c:264:9: error: implicit declaration of function 'do_epoll_ctl'; did you mean 'sys_epoll_ctl'? [-Werror=implicit-function-declaration]
  264 |  return do_epoll_ctl(epfd, op, fd, &kernel, false);
      |         ^~~~~~~~~~~~

Fixes: c281634c8652 ("ARM: compat: remove KERNEL_DS usage in sys_oabi_epoll_ctl()")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: kernel test robot <lkp@intel.com> # from an lkp .config file
Cc: Russell King <linux@armlinux.org.uk>
Cc: linux-arm-kernel@lists.infradead.org
Cc: Nicolas Pitre <nico@fluxnic.net>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: patches@armlinux.org.uk
Acked-by: Nicolas Pitre <nico@fluxnic.net>
---
KernelVersion: v5.11
I don't know what format is used for KernelVersion.
This patch applies to any Linux kernel v5.x and probably even older.

v2: use correct Fixes: tag (thanks, rmk)
v3: add patches@ to Cc: list
v4: add KernelVersion for Patch Daemon; add Acked-by from nico@)

 arch/arm/kernel/sys_oabi-compat.c |   15 +++++++++++++++
 1 file changed, 15 insertions(+)

--- linux-next-20201214.orig/arch/arm/kernel/sys_oabi-compat.c
+++ linux-next-20201214/arch/arm/kernel/sys_oabi-compat.c
@@ -248,6 +248,7 @@ struct oabi_epoll_event {
 	__u64 data;
 } __attribute__ ((packed,aligned(4)));
 
+#ifdef CONFIG_EPOLL
 asmlinkage long sys_oabi_epoll_ctl(int epfd, int op, int fd,
 				   struct oabi_epoll_event __user *event)
 {
@@ -298,6 +299,20 @@ asmlinkage long sys_oabi_epoll_wait(int
 	kfree(kbuf);
 	return err ? -EFAULT : ret;
 }
+#else
+asmlinkage long sys_oabi_epoll_ctl(int epfd, int op, int fd,
+				   struct oabi_epoll_event __user *event)
+{
+	return -EINVAL;
+}
+
+asmlinkage long sys_oabi_epoll_wait(int epfd,
+				    struct oabi_epoll_event __user *events,
+				    int maxevents, int timeout)
+{
+	return -EINVAL;
+}
+#endif
 
 struct oabi_sembuf {
 	unsigned short	sem_num;