eabc069401
This patch (as751) adds a new type of notifier chain, based on the SRCU (Sleepable Read-Copy Update) primitives recently added to the kernel. An SRCU notifier chain is much like a blocking notifier chain, in that it must be called in process context and its callout routines are allowed to sleep. The difference is that the chain's links are protected by the SRCU mechanism rather than by an rw-semaphore, so calling the chain has extremely low overhead: no memory barriers and no cache-line bouncing. On the other hand, unregistering from the chain is expensive and the chain head requires special runtime initialization (plus cleanup if it is to be deallocated). SRCU notifiers are appropriate for notifiers that will be called very frequently and for which unregistration occurs very seldom. The proposed "task notifier" scheme qualifies, as may some of the network notifiers. Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Acked-by: Paul E. McKenney <paulmck@us.ibm.com> Acked-by: Chandra Seetharaman <sekharan@us.ibm.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
191 lines
6.8 KiB
C
191 lines
6.8 KiB
C
/*
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* Routines to manage notifier chains for passing status changes to any
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* interested routines. We need this instead of hard coded call lists so
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* that modules can poke their nose into the innards. The network devices
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* needed them so here they are for the rest of you.
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*
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* Alan Cox <Alan.Cox@linux.org>
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*/
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#ifndef _LINUX_NOTIFIER_H
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#define _LINUX_NOTIFIER_H
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#include <linux/errno.h>
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#include <linux/mutex.h>
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#include <linux/rwsem.h>
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#include <linux/srcu.h>
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/*
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* Notifier chains are of four types:
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*
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* Atomic notifier chains: Chain callbacks run in interrupt/atomic
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* context. Callouts are not allowed to block.
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* Blocking notifier chains: Chain callbacks run in process context.
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* Callouts are allowed to block.
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* Raw notifier chains: There are no restrictions on callbacks,
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* registration, or unregistration. All locking and protection
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* must be provided by the caller.
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* SRCU notifier chains: A variant of blocking notifier chains, with
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* the same restrictions.
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*
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* atomic_notifier_chain_register() may be called from an atomic context,
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* but blocking_notifier_chain_register() and srcu_notifier_chain_register()
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* must be called from a process context. Ditto for the corresponding
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* _unregister() routines.
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*
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* atomic_notifier_chain_unregister(), blocking_notifier_chain_unregister(),
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* and srcu_notifier_chain_unregister() _must not_ be called from within
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* the call chain.
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*
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* SRCU notifier chains are an alternative form of blocking notifier chains.
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* They use SRCU (Sleepable Read-Copy Update) instead of rw-semaphores for
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* protection of the chain links. This means there is _very_ low overhead
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* in srcu_notifier_call_chain(): no cache bounces and no memory barriers.
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* As compensation, srcu_notifier_chain_unregister() is rather expensive.
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* SRCU notifier chains should be used when the chain will be called very
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* often but notifier_blocks will seldom be removed. Also, SRCU notifier
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* chains are slightly more difficult to use because they require special
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* runtime initialization.
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*/
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struct notifier_block {
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int (*notifier_call)(struct notifier_block *, unsigned long, void *);
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struct notifier_block *next;
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int priority;
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};
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struct atomic_notifier_head {
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spinlock_t lock;
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struct notifier_block *head;
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};
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struct blocking_notifier_head {
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struct rw_semaphore rwsem;
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struct notifier_block *head;
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};
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struct raw_notifier_head {
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struct notifier_block *head;
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};
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struct srcu_notifier_head {
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struct mutex mutex;
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struct srcu_struct srcu;
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struct notifier_block *head;
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};
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#define ATOMIC_INIT_NOTIFIER_HEAD(name) do { \
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spin_lock_init(&(name)->lock); \
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(name)->head = NULL; \
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} while (0)
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#define BLOCKING_INIT_NOTIFIER_HEAD(name) do { \
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init_rwsem(&(name)->rwsem); \
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(name)->head = NULL; \
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} while (0)
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#define RAW_INIT_NOTIFIER_HEAD(name) do { \
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(name)->head = NULL; \
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} while (0)
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/* srcu_notifier_heads must be initialized and cleaned up dynamically */
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extern void srcu_init_notifier_head(struct srcu_notifier_head *nh);
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#define srcu_cleanup_notifier_head(name) \
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cleanup_srcu_struct(&(name)->srcu);
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#define ATOMIC_NOTIFIER_INIT(name) { \
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.lock = __SPIN_LOCK_UNLOCKED(name.lock), \
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.head = NULL }
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#define BLOCKING_NOTIFIER_INIT(name) { \
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.rwsem = __RWSEM_INITIALIZER((name).rwsem), \
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.head = NULL }
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#define RAW_NOTIFIER_INIT(name) { \
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.head = NULL }
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/* srcu_notifier_heads cannot be initialized statically */
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#define ATOMIC_NOTIFIER_HEAD(name) \
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struct atomic_notifier_head name = \
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ATOMIC_NOTIFIER_INIT(name)
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#define BLOCKING_NOTIFIER_HEAD(name) \
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struct blocking_notifier_head name = \
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BLOCKING_NOTIFIER_INIT(name)
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#define RAW_NOTIFIER_HEAD(name) \
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struct raw_notifier_head name = \
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RAW_NOTIFIER_INIT(name)
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#ifdef __KERNEL__
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extern int atomic_notifier_chain_register(struct atomic_notifier_head *,
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struct notifier_block *);
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extern int blocking_notifier_chain_register(struct blocking_notifier_head *,
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struct notifier_block *);
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extern int raw_notifier_chain_register(struct raw_notifier_head *,
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struct notifier_block *);
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extern int srcu_notifier_chain_register(struct srcu_notifier_head *,
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struct notifier_block *);
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extern int atomic_notifier_chain_unregister(struct atomic_notifier_head *,
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struct notifier_block *);
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extern int blocking_notifier_chain_unregister(struct blocking_notifier_head *,
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struct notifier_block *);
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extern int raw_notifier_chain_unregister(struct raw_notifier_head *,
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struct notifier_block *);
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extern int srcu_notifier_chain_unregister(struct srcu_notifier_head *,
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struct notifier_block *);
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extern int atomic_notifier_call_chain(struct atomic_notifier_head *,
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unsigned long val, void *v);
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extern int blocking_notifier_call_chain(struct blocking_notifier_head *,
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unsigned long val, void *v);
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extern int raw_notifier_call_chain(struct raw_notifier_head *,
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unsigned long val, void *v);
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extern int srcu_notifier_call_chain(struct srcu_notifier_head *,
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unsigned long val, void *v);
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#define NOTIFY_DONE 0x0000 /* Don't care */
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#define NOTIFY_OK 0x0001 /* Suits me */
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#define NOTIFY_STOP_MASK 0x8000 /* Don't call further */
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#define NOTIFY_BAD (NOTIFY_STOP_MASK|0x0002)
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/* Bad/Veto action */
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/*
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* Clean way to return from the notifier and stop further calls.
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*/
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#define NOTIFY_STOP (NOTIFY_OK|NOTIFY_STOP_MASK)
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/*
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* Declared notifiers so far. I can imagine quite a few more chains
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* over time (eg laptop power reset chains, reboot chain (to clean
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* device units up), device [un]mount chain, module load/unload chain,
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* low memory chain, screenblank chain (for plug in modular screenblankers)
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* VC switch chains (for loadable kernel svgalib VC switch helpers) etc...
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*/
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/* netdevice notifier chain */
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#define NETDEV_UP 0x0001 /* For now you can't veto a device up/down */
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#define NETDEV_DOWN 0x0002
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#define NETDEV_REBOOT 0x0003 /* Tell a protocol stack a network interface
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detected a hardware crash and restarted
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- we can use this eg to kick tcp sessions
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once done */
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#define NETDEV_CHANGE 0x0004 /* Notify device state change */
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#define NETDEV_REGISTER 0x0005
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#define NETDEV_UNREGISTER 0x0006
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#define NETDEV_CHANGEMTU 0x0007
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#define NETDEV_CHANGEADDR 0x0008
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#define NETDEV_GOING_DOWN 0x0009
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#define NETDEV_CHANGENAME 0x000A
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#define NETDEV_FEAT_CHANGE 0x000B
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#define SYS_DOWN 0x0001 /* Notify of system down */
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#define SYS_RESTART SYS_DOWN
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#define SYS_HALT 0x0002 /* Notify of system halt */
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#define SYS_POWER_OFF 0x0003 /* Notify of system power off */
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#define NETLINK_URELEASE 0x0001 /* Unicast netlink socket released */
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#define CPU_ONLINE 0x0002 /* CPU (unsigned)v is up */
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#define CPU_UP_PREPARE 0x0003 /* CPU (unsigned)v coming up */
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#define CPU_UP_CANCELED 0x0004 /* CPU (unsigned)v NOT coming up */
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#define CPU_DOWN_PREPARE 0x0005 /* CPU (unsigned)v going down */
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#define CPU_DOWN_FAILED 0x0006 /* CPU (unsigned)v NOT going down */
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#define CPU_DEAD 0x0007 /* CPU (unsigned)v dead */
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#endif /* __KERNEL__ */
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#endif /* _LINUX_NOTIFIER_H */
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