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
  51 struct notifier_block;
  52
  53 typedef int (*notifier_fn_t)(struct notifier_block *nb,
  54                         unsigned long action, void *data);
  55
  56 struct notifier_block {
  57         notifier_fn_t notifier_call;
  58         struct notifier_block __rcu *next;
  59         int priority;
  60 };
  61
  62 struct atomic_notifier_head {
  63         spinlock_t lock;
  64         struct notifier_block __rcu *head;
  65 };
  66
  67 struct blocking_notifier_head {
  68         struct rw_semaphore rwsem;
  69         struct notifier_block __rcu *head;
  70 };
  71
  72 struct raw_notifier_head {
  73         struct notifier_block __rcu *head;
  74 };
  75
  76 struct 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 */
  95 extern 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
 121 extern int atomic_notifier_chain_register(struct atomic_notifier_head *nh,
 122                 struct notifier_block *nb);
 123 extern int blocking_notifier_chain_register(struct blocking_notifier_head *nh,
 124                 struct notifier_block *nb);
 125 extern int raw_notifier_chain_register(struct raw_notifier_head *nh,
 126                 struct notifier_block *nb);
 127 extern int srcu_notifier_chain_register(struct srcu_notifier_head *nh,
 128                 struct notifier_block *nb);
 129
 130 extern int blocking_notifier_chain_cond_register(
 131                 struct blocking_notifier_head *nh,
 132                 struct notifier_block *nb);
 133
 134 extern int atomic_notifier_chain_unregister(struct atomic_notifier_head *nh,
 135                 struct notifier_block *nb);
 136 extern int blocking_notifier_chain_unregister(struct blocking_notifier_head *nh,
 137                 struct notifier_block *nb);
 138 extern int raw_notifier_chain_unregister(struct raw_notifier_head *nh,
 139                 struct notifier_block *nb);
 140 extern int srcu_notifier_chain_unregister(struct srcu_notifier_head *nh,
 141                 struct notifier_block *nb);
 142
 143 extern int atomic_notifier_call_chain(struct atomic_notifier_head *nh,
 144                 unsigned long val, void *v);
 145 extern int __atomic_notifier_call_chain(struct atomic_notifier_head *nh,
 146         unsigned long val, void *v, int nr_to_call, int *nr_calls);
 147 extern int blocking_notifier_call_chain(struct blocking_notifier_head *nh,
 148                 unsigned long val, void *v);
 149 extern int __blocking_notifier_call_chain(struct blocking_notifier_head *nh,
 150         unsigned long val, void *v, int nr_to_call, int *nr_calls);
 151 extern int raw_notifier_call_chain(struct raw_notifier_head *nh,
 152                 unsigned long val, void *v);
 153 extern int __raw_notifier_call_chain(struct raw_notifier_head *nh,
 154         unsigned long val, void *v, int nr_to_call, int *nr_calls);
 155 extern int srcu_notifier_call_chain(struct srcu_notifier_head *nh,
 156                 unsigned long val, void *v);
 157 extern 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). */
 171 static 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. */
 180 static 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
 215 extern struct blocking_notifier_head reboot_notifier_list;
 216
 217 #endif /* __KERNEL__ */
 218 #endif /* _LINUX_NOTIFIER_H */