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.
  47  */
  48
  49 struct notifier_block;
  50
  51 typedef int (*notifier_fn_t)(struct notifier_block *nb,
  52                         unsigned long action, void *data);
  53
  54 struct notifier_block {
  55         notifier_fn_t notifier_call;
  56         struct notifier_block __rcu *next;
  57         int priority;
  58 };
  59
  60 struct atomic_notifier_head {
  61         spinlock_t lock;
  62         struct notifier_block __rcu *head;
  63 };
  64
  65 struct blocking_notifier_head {
  66         struct rw_semaphore rwsem;
  67         struct notifier_block __rcu *head;
  68 };
  69
  70 struct raw_notifier_head {
  71         struct notifier_block __rcu *head;
  72 };
  73
  74 struct srcu_notifier_head {
  75         struct mutex mutex;
  76         struct srcu_struct srcu;
  77         struct notifier_block __rcu *head;
  78 };
  79
  80 #define ATOMIC_INIT_NOTIFIER_HEAD(name) do {    \
  81                 spin_lock_init(&(name)->lock);  \
  82                 (name)->head = NULL;            \
  83         } while (0)
  84 #define BLOCKING_INIT_NOTIFIER_HEAD(name) do {  \
  85                 init_rwsem(&(name)->rwsem);     \
  86                 (name)->head = NULL;            \
  87         } while (0)
  88 #define RAW_INIT_NOTIFIER_HEAD(name) do {       \
  89                 (name)->head = NULL;            \
  90         } while (0)
  91
  92 /* srcu_notifier_heads must be cleaned up dynamically */
  93 extern void srcu_init_notifier_head(struct srcu_notifier_head *nh);
  94 #define srcu_cleanup_notifier_head(name)        \
  95                 cleanup_srcu_struct(&(name)->srcu);
  96
  97 #define ATOMIC_NOTIFIER_INIT(name) {                            \
  98                 .lock = __SPIN_LOCK_UNLOCKED(name.lock),        \
  99                 .head = NULL }
 100 #define BLOCKING_NOTIFIER_INIT(name) {                          \
 101                 .rwsem = __RWSEM_INITIALIZER((name).rwsem),     \
 102                 .head = NULL }
 103 #define RAW_NOTIFIER_INIT(name) {                               \
 104                 .head = NULL }
 105
 106 #define SRCU_NOTIFIER_INIT(name, pcpu)                          \
 107         {                                                       \
 108                 .mutex = __MUTEX_INITIALIZER(name.mutex),       \
 109                 .head = NULL,                                   \
 110                 .srcu = __SRCU_STRUCT_INIT(name.srcu, pcpu),    \
 111         }
 112
 113 #define ATOMIC_NOTIFIER_HEAD(name)                              \
 114         struct atomic_notifier_head name =                      \
 115                 ATOMIC_NOTIFIER_INIT(name)
 116 #define BLOCKING_NOTIFIER_HEAD(name)                            \
 117         struct blocking_notifier_head name =                    \
 118                 BLOCKING_NOTIFIER_INIT(name)
 119 #define RAW_NOTIFIER_HEAD(name)                                 \
 120         struct raw_notifier_head name =                         \
 121                 RAW_NOTIFIER_INIT(name)
 122
 123 #ifdef CONFIG_TREE_SRCU
 124 #define _SRCU_NOTIFIER_HEAD(name, mod)                          \
 125         static DEFINE_PER_CPU(struct srcu_data, name##_head_srcu_data); \
 126         mod struct srcu_notifier_head name =                    \
 127                         SRCU_NOTIFIER_INIT(name, name##_head_srcu_data)
 128
 129 #else
 130 #define _SRCU_NOTIFIER_HEAD(name, mod)                          \
 131         mod struct srcu_notifier_head name =                    \
 132                         SRCU_NOTIFIER_INIT(name, name)
 133
 134 #endif
 135
 136 #define SRCU_NOTIFIER_HEAD(name)                                \
 137         _SRCU_NOTIFIER_HEAD(name, /* not static */)
 138
 139 #define SRCU_NOTIFIER_HEAD_STATIC(name)                         \
 140         _SRCU_NOTIFIER_HEAD(name, static)
 141
 142 #ifdef __KERNEL__
 143
 144 extern int atomic_notifier_chain_register(struct atomic_notifier_head *nh,
 145                 struct notifier_block *nb);
 146 extern int blocking_notifier_chain_register(struct blocking_notifier_head *nh,
 147                 struct notifier_block *nb);
 148 extern int raw_notifier_chain_register(struct raw_notifier_head *nh,
 149                 struct notifier_block *nb);
 150 extern int srcu_notifier_chain_register(struct srcu_notifier_head *nh,
 151                 struct notifier_block *nb);
 152
 153 extern int atomic_notifier_chain_unregister(struct atomic_notifier_head *nh,
 154                 struct notifier_block *nb);
 155 extern int blocking_notifier_chain_unregister(struct blocking_notifier_head *nh,
 156                 struct notifier_block *nb);
 157 extern int raw_notifier_chain_unregister(struct raw_notifier_head *nh,
 158                 struct notifier_block *nb);
 159 extern int srcu_notifier_chain_unregister(struct srcu_notifier_head *nh,
 160                 struct notifier_block *nb);
 161
 162 extern int atomic_notifier_call_chain(struct atomic_notifier_head *nh,
 163                 unsigned long val, void *v);
 164 extern int blocking_notifier_call_chain(struct blocking_notifier_head *nh,
 165                 unsigned long val, void *v);
 166 extern int raw_notifier_call_chain(struct raw_notifier_head *nh,
 167                 unsigned long val, void *v);
 168 extern int srcu_notifier_call_chain(struct srcu_notifier_head *nh,
 169                 unsigned long val, void *v);
 170
 171 extern int blocking_notifier_call_chain_robust(struct blocking_notifier_head *nh,
 172                 unsigned long val_up, unsigned long val_down, void *v);
 173 extern int raw_notifier_call_chain_robust(struct raw_notifier_head *nh,
 174                 unsigned long val_up, unsigned long val_down, void *v);
 175
 176 #define NOTIFY_DONE             0x0000          /* Don't care */
 177 #define NOTIFY_OK               0x0001          /* Suits me */
 178 #define NOTIFY_STOP_MASK        0x8000          /* Don't call further */
 179 #define NOTIFY_BAD              (NOTIFY_STOP_MASK|0x0002)
 180                                                 /* Bad/Veto action */
 181 /*
 182  * Clean way to return from the notifier and stop further calls.
 183  */
 184 #define NOTIFY_STOP             (NOTIFY_OK|NOTIFY_STOP_MASK)
 185
 186 /* Encapsulate (negative) errno value (in particular, NOTIFY_BAD <=> EPERM). */
 187 static inline int notifier_from_errno(int err)
 188 {
 189         if (err)
 190                 return NOTIFY_STOP_MASK | (NOTIFY_OK - err);
 191
 192         return NOTIFY_OK;
 193 }
 194
 195 /* Restore (negative) errno value from notify return value. */
 196 static inline int notifier_to_errno(int ret)
 197 {
 198         ret &= ~NOTIFY_STOP_MASK;
 199         return ret > NOTIFY_OK ? NOTIFY_OK - ret : 0;
 200 }
 201
 202 /*
 203  *      Declared notifiers so far. I can imagine quite a few more chains
 204  *      over time (eg laptop power reset chains, reboot chain (to clean
 205  *      device units up), device [un]mount chain, module load/unload chain,
 206  *      low memory chain, screenblank chain (for plug in modular screenblankers)
 207  *      VC switch chains (for loadable kernel svgalib VC switch helpers) etc...
 208  */
 209
 210 /* CPU notfiers are defined in include/linux/cpu.h. */
 211
 212 /* netdevice notifiers are defined in include/linux/netdevice.h */
 213
 214 /* reboot notifiers are defined in include/linux/reboot.h. */
 215
 216 /* Hibernation and suspend events are defined in include/linux/suspend.h. */
 217
 218 /* Virtual Terminal events are defined in include/linux/vt.h. */
 219
 220 #define NETLINK_URELEASE        0x0001  /* Unicast netlink socket released */
 221
 222 /* Console keyboard events.
 223  * Note: KBD_KEYCODE is always sent before KBD_UNBOUND_KEYCODE, KBD_UNICODE and
 224  * KBD_KEYSYM. */
 225 #define KBD_KEYCODE             0x0001 /* Keyboard keycode, called before any other */
 226 #define KBD_UNBOUND_KEYCODE     0x0002 /* Keyboard keycode which is not bound to any other */
 227 #define KBD_UNICODE             0x0003 /* Keyboard unicode */
 228 #define KBD_KEYSYM              0x0004 /* Keyboard keysym */
 229 #define KBD_POST_KEYSYM         0x0005 /* Called after keyboard keysym interpretation */
 230
 231 extern struct blocking_notifier_head reboot_notifier_list;
 232
 233 #endif /* __KERNEL__ */
 234 #endif /* _LINUX_NOTIFIER_H */