[PATCH] kernfs: add stub helper for kernfs_generic_poll()

[Arnd Bergmann <arnd@kernel.org>]

From: Arnd Bergmann <arnd@arndb.de>

In some randconfig builds, kernfs ends up being disabled, so there is no prototype
for kernfs_generic_poll()

In file included from kernel/sched/build_utility.c:97:
kernel/sched/psi.c:1479:3: error: implicit declaration of function 'kernfs_generic_poll' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
                kernfs_generic_poll(t->of, wait);
                ^

Add a stub helper for it, as we have it for other kernfs functions.

Fixes: aff037078ecae ("sched/psi: use kernfs polling functions for PSI trigger polling")
Fixes: 147e1a97c4a0b ("fs: kernfs: add poll file operation")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
While the stub was always missing, this only caused problems now that sched/psi.c
calls it unconditionally. The patch that caused it was already merged into v6.5-rc2
---
 include/linux/kernfs.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index 73f5c120def88..2a36f3218b510 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -550,6 +550,10 @@ static inline int kernfs_setattr(struct kernfs_node *kn,
 				 const struct iattr *iattr)
 { return -ENOSYS; }
 
+static inline __poll_t kernfs_generic_poll(struct kernfs_open_file *of,
+					   struct poll_table_struct *pt)
+{ return -ENOSYS; }
+
 static inline void kernfs_notify(struct kernfs_node *kn) { }
 
 static inline int kernfs_xattr_get(struct kernfs_node *kn, const char *name,
-- 
2.39.2