1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * Copyright (c) 2022-2024 Oracle.  All Rights Reserved.
4 * Author: Darrick J. Wong <djwong@kernel.org>
5 */
6#ifndef XFS_HOOKS_H_
7#define XFS_HOOKS_H_
8
9#ifdef CONFIG_XFS_LIVE_HOOKS
10struct xfs_hooks {
11	struct blocking_notifier_head	head;
12};
13
14/*
15 * If jump labels are enabled in Kconfig, the static key uses nop sleds and
16 * code patching to eliminate the overhead of taking the rwsem in
17 * blocking_notifier_call_chain when there are no hooks configured.  If not,
18 * the static key per-call overhead is an atomic read.  Most arches that can
19 * handle XFS also support jump labels.
20 *
21 * Note: Patching the kernel code requires taking the cpu hotplug lock.  Other
22 * parts of the kernel allocate memory with that lock held, which means that
23 * XFS callers cannot hold any locks that might be used by memory reclaim or
24 * writeback when calling the static_branch_{inc,dec} functions.
25 */
26# define DEFINE_STATIC_XFS_HOOK_SWITCH(name) \
27	static DEFINE_STATIC_KEY_FALSE(name)
28# define xfs_hooks_switch_on(name)	static_branch_inc(name)
29# define xfs_hooks_switch_off(name)	static_branch_dec(name)
30# define xfs_hooks_switched_on(name)	static_branch_unlikely(name)
31
32struct xfs_hook {
33	/* This must come at the start of the structure. */
34	struct notifier_block		nb;
35};
36
37typedef	int (*xfs_hook_fn_t)(struct xfs_hook *hook, unsigned long action,
38		void *data);
39
40void xfs_hooks_init(struct xfs_hooks *chain);
41int xfs_hooks_add(struct xfs_hooks *chain, struct xfs_hook *hook);
42void xfs_hooks_del(struct xfs_hooks *chain, struct xfs_hook *hook);
43int xfs_hooks_call(struct xfs_hooks *chain, unsigned long action,
44		void *priv);
45
46static inline void xfs_hook_setup(struct xfs_hook *hook, notifier_fn_t fn)
47{
48	hook->nb.notifier_call = fn;
49	hook->nb.priority = 0;
50}
51
52#else
53
54struct xfs_hooks { /* empty */ };
55
56# define DEFINE_STATIC_XFS_HOOK_SWITCH(name)
57# define xfs_hooks_switch_on(name)		((void)0)
58# define xfs_hooks_switch_off(name)		((void)0)
59# define xfs_hooks_switched_on(name)		(false)
60
61# define xfs_hooks_init(chain)			((void)0)
62# define xfs_hooks_call(chain, val, priv)	(NOTIFY_DONE)
63#endif
64
65#endif /* XFS_HOOKS_H_ */
66