LXR linux/include/linux/notifier.h

   1/* SPDX-License-Identifier: GPL-2.0 */
   2/*
   3 *      Routines to manage notifier chains for passing status changes to any
   4 *      interested routines. We need this instead of hard coded call lists so
   5 *      that modules can poke their nose into the innards. The network devices
   6 *      needed them so here they are for the rest of you.
   7 *
   8 *                              Alan Cox <Alan.Cox@linux.org>
   9 */
  10 
  11#ifndef _LINUX_NOTIFIER_H
  12#define _LINUX_NOTIFIER_H
  13#include <linux/errno.h>
  14#include <linux/mutex.h>
  15#include <linux/rwsem.h>
  16#include <linux/srcu.h>
  17
  18/*
  19 * Notifier chains are of four types:
  20 *
  21 *      Atomic notifier chains: Chain callbacks run in interrupt/atomic
  22 *              context. Callouts are not allowed to block.
  23 *      Blocking notifier chains: Chain callbacks run in process context.
  24 *              Callouts are allowed to block.
  25 *      Raw notifier chains: There are no restrictions on callbacks,
  26 *              registration, or unregistration.  All locking and protection
  27 *              must be provided by the caller.
  28 *      SRCU notifier chains: A variant of blocking notifier chains, with
  29 *              the same restrictions.
  30 *
  31 * atomic_notifier_chain_register() may be called from an atomic context,
  32 * but blocking_notifier_chain_register() and srcu_notifier_chain_register()
  33 * must be called from a process context.  Ditto for the corresponding
  34 * _unregister() routines.
  35 *
  36 * atomic_notifier_chain_unregister(), blocking_notifier_chain_unregister(),
  37 * and srcu_notifier_chain_unregister() _must not_ be called from within
  38 * the call chain.
  39 *
  40 * SRCU notifier chains are an alternative form of blocking notifier chains.
  41 * They use SRCU (Sleepable Read-Copy Update) instead of rw-semaphores for
  42 * protection of the chain links.  This means there is _very_ low overhead
  43 * in srcu_notifier_call_chain(): no cache bounces and no memory barriers.
  44 * As compensation, srcu_notifier_chain_unregister() is rather expensive.
  45 * SRCU notifier chains should be used when the chain will be called very
  46 * often but notifier_blocks will seldom be removed.  Also, SRCU notifier
  47 * chains are slightly more difficult to use because they require special
  48 * runtime initialization.
  49 */
  50
  51struct notifier_block;
  52
  53typedef int (*notifier_fn_t)(struct notifier_block *nb,
  54                        unsigned long action, void *data);
  55
  56struct notifier_block {
  57        notifier_fn_t notifier_call;
  58        struct notifier_block __rcu *next;
  59        int priority;
  60};
  61
  62struct atomic_notifier_head {
  63        spinlock_t lock;
  64        struct notifier_block __rcu *head;
  65};
  66
  67struct blocking_notifier_head {
  68        struct rw_semaphore rwsem;
  69        struct notifier_block __rcu *head;
  70};
  71
  72struct raw_notifier_head {
  73        struct notifier_block __rcu *head;
  74};
  75
  76struct srcu_notifier_head {
  77        struct mutex mutex;
  78        struct srcu_struct srcu;
  79        struct notifier_block __rcu *head;
  80};
  81
  82#define ATOMIC_INIT_NOTIFIER_HEAD(name) do {    \
  83                spin_lock_init(&(name)->lock);  \
  84                (name)->head = NULL;            \
  85        } while (0)
  86#define BLOCKING_INIT_NOTIFIER_HEAD(name) do {  \
  87                init_rwsem(&(name)->rwsem);     \
  88                (name)->head = NULL;            \
  89        } while (0)
  90#define RAW_INIT_NOTIFIER_HEAD(name) do {       \
  91                (name)->head = NULL;            \
  92        } while (0)
  93
  94/* srcu_notifier_heads must be initialized and cleaned up dynamically */
  95extern void srcu_init_notifier_head(struct srcu_notifier_head *nh);
  96#define srcu_cleanup_notifier_head(name)        \
  97                cleanup_srcu_struct(&(name)->srcu);
  98
  99#define ATOMIC_NOTIFIER_INIT(name) {                            \
 100                .lock = __SPIN_LOCK_UNLOCKED(name.lock),        \
 101                .head = NULL }
 102#define BLOCKING_NOTIFIER_INIT(name) {                          \
 103                .rwsem = __RWSEM_INITIALIZER((name).rwsem),     \
 104                .head = NULL }
 105#define RAW_NOTIFIER_INIT(name) {                               \
 106                .head = NULL }
 107/* srcu_notifier_heads cannot be initialized statically */
 108
 109#define ATOMIC_NOTIFIER_HEAD(name)                              \
 110        struct atomic_notifier_head name =                      \
 111                ATOMIC_NOTIFIER_INIT(name)
 112#define BLOCKING_NOTIFIER_HEAD(name)                            \
 113        struct blocking_notifier_head name =                    \
 114                BLOCKING_NOTIFIER_INIT(name)
 115#define RAW_NOTIFIER_HEAD(name)                                 \
 116        struct raw_notifier_head name =                         \
 117                RAW_NOTIFIER_INIT(name)
 118
 119#ifdef __KERNEL__
 120
 121extern int atomic_notifier_chain_register(struct atomic_notifier_head *nh,
 122                struct notifier_block *nb);
 123extern int blocking_notifier_chain_register(struct blocking_notifier_head *nh,
 124                struct notifier_block *nb);
 125extern int raw_notifier_chain_register(struct raw_notifier_head *nh,
 126                struct notifier_block *nb);
 127extern int srcu_notifier_chain_register(struct srcu_notifier_head *nh,
 128                struct notifier_block *nb);
 129
 130extern int blocking_notifier_chain_cond_register(
 131                struct blocking_notifier_head *nh,
 132                struct notifier_block *nb);
 133
 134extern int atomic_notifier_chain_unregister(struct atomic_notifier_head *nh,
 135                struct notifier_block *nb);
 136extern int blocking_notifier_chain_unregister(struct blocking_notifier_head *nh,
 137                struct notifier_block *nb);
 138extern int raw_notifier_chain_unregister(struct raw_notifier_head *nh,
 139                struct notifier_block *nb);
 140extern int srcu_notifier_chain_unregister(struct srcu_notifier_head *nh,
 141                struct notifier_block *nb);
 142
 143extern int atomic_notifier_call_chain(struct atomic_notifier_head *nh,
 144                unsigned long val, void *v);
 145extern int __atomic_notifier_call_chain(struct atomic_notifier_head *nh,
 146        unsigned long val, void *v, int nr_to_call, int *nr_calls);
 147extern int blocking_notifier_call_chain(struct blocking_notifier_head *nh,
 148                unsigned long val, void *v);
 149extern int __blocking_notifier_call_chain(struct blocking_notifier_head *nh,
 150        unsigned long val, void *v, int nr_to_call, int *nr_calls);
 151extern int raw_notifier_call_chain(struct raw_notifier_head *nh,
 152                unsigned long val, void *v);
 153extern int __raw_notifier_call_chain(struct raw_notifier_head *nh,
 154        unsigned long val, void *v, int nr_to_call, int *nr_calls);
 155extern int srcu_notifier_call_chain(struct srcu_notifier_head *nh,
 156                unsigned long val, void *v);
 157extern int __srcu_notifier_call_chain(struct srcu_notifier_head *nh,
 158        unsigned long val, void *v, int nr_to_call, int *nr_calls);
 159
 160#define NOTIFY_DONE             0x0000          /* Don't care */
 161#define NOTIFY_OK               0x0001          /* Suits me */
 162#define NOTIFY_STOP_MASK        0x8000          /* Don't call further */
 163#define NOTIFY_BAD              (NOTIFY_STOP_MASK|0x0002)
 164                                                /* Bad/Veto action */
 165/*
 166 * Clean way to return from the notifier and stop further calls.
 167 */
 168#define NOTIFY_STOP             (NOTIFY_OK|NOTIFY_STOP_MASK)
 169
 170/* Encapsulate (negative) errno value (in particular, NOTIFY_BAD <=> EPERM). */
 171static inline int notifier_from_errno(int err)
 172{
 173        if (err)
 174                return NOTIFY_STOP_MASK | (NOTIFY_OK - err);
 175
 176        return NOTIFY_OK;
 177}
 178
 179/* Restore (negative) errno value from notify return value. */
 180static inline int notifier_to_errno(int ret)
 181{
 182        ret &= ~NOTIFY_STOP_MASK;
 183        return ret > NOTIFY_OK ? NOTIFY_OK - ret : 0;
 184}
 185
 186/*
 187 *      Declared notifiers so far. I can imagine quite a few more chains
 188 *      over time (eg laptop power reset chains, reboot chain (to clean 
 189 *      device units up), device [un]mount chain, module load/unload chain,
 190 *      low memory chain, screenblank chain (for plug in modular screenblankers) 
 191 *      VC switch chains (for loadable kernel svgalib VC switch helpers) etc...
 192 */
 193 
 194/* CPU notfiers are defined in include/linux/cpu.h. */
 195
 196/* netdevice notifiers are defined in include/linux/netdevice.h */
 197
 198/* reboot notifiers are defined in include/linux/reboot.h. */
 199
 200/* Hibernation and suspend events are defined in include/linux/suspend.h. */
 201
 202/* Virtual Terminal events are defined in include/linux/vt.h. */
 203
 204#define NETLINK_URELEASE        0x0001  /* Unicast netlink socket released */
 205
 206/* Console keyboard events.
 207 * Note: KBD_KEYCODE is always sent before KBD_UNBOUND_KEYCODE, KBD_UNICODE and
 208 * KBD_KEYSYM. */
 209#define KBD_KEYCODE             0x0001 /* Keyboard keycode, called before any other */
 210#define KBD_UNBOUND_KEYCODE     0x0002 /* Keyboard keycode which is not bound to any other */
 211#define KBD_UNICODE             0x0003 /* Keyboard unicode */
 212#define KBD_KEYSYM              0x0004 /* Keyboard keysym */
 213#define KBD_POST_KEYSYM         0x0005 /* Called after keyboard keysym interpretation */
 214
 215extern struct blocking_notifier_head reboot_notifier_list;
 216
 217#endif /* __KERNEL__ */
 218#endif /* _LINUX_NOTIFIER_H */
 219