fs/xfs/xfs_hooks.h

   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
  10 struct 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
  32 struct xfs_hook {
  33         /* This must come at the start of the structure. */
  34         struct notifier_block           nb;
  35 };
  36
  37 typedef int (*xfs_hook_fn_t)(struct xfs_hook *hook, unsigned long action,
  38                 void *data);
  39
  40 void xfs_hooks_init(struct xfs_hooks *chain);
  41 int xfs_hooks_add(struct xfs_hooks *chain, struct xfs_hook *hook);
  42 void xfs_hooks_del(struct xfs_hooks *chain, struct xfs_hook *hook);
  43 int xfs_hooks_call(struct xfs_hooks *chain, unsigned long action,
  44                 void *priv);
  45
  46 static 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
  54 struct 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_ */