| /* |
| * kref.h - library routines for handling generic reference counted objects |
| * |
| * Copyright (C) 2004 Greg Kroah-Hartman <greg@kroah.com> |
| * Copyright (C) 2004 IBM Corp. |
| * |
| * based on kobject.h which was: |
| * Copyright (C) 2002-2003 Patrick Mochel <mochel@osdl.org> |
| * Copyright (C) 2002-2003 Open Source Development Labs |
| * |
| * This file is released under the GPLv2. |
| * |
| */ |
| |
| #ifndef _KREF_H_ |
| #define _KREF_H_ |
| |
| #include <linux/bug.h> |
| #include <linux/atomic.h> |
| #include <linux/kernel.h> |
| |
| struct kref { |
| atomic_t refcount; |
| }; |
| |
| /** |
| * kref_init - initialize object. |
| * @kref: object in question. |
| */ |
| static inline void kref_init(struct kref *kref) |
| { |
| atomic_set(&kref->refcount, 1); |
| } |
| |
| /** |
| * kref_get - increment refcount for object. |
| * @kref: object. |
| */ |
| static inline void kref_get(struct kref *kref) |
| { |
| WARN_ON(!atomic_read(&kref->refcount)); |
| atomic_inc(&kref->refcount); |
| } |
| |
| /** |
| * kref_sub - subtract a number of refcounts for object. |
| * @kref: object. |
| * @count: Number of recounts to subtract. |
| * @release: pointer to the function that will clean up the object when the |
| * last reference to the object is released. |
| * This pointer is required, and it is not acceptable to pass kfree |
| * in as this function. If the caller does pass kfree to this |
| * function, you will be publicly mocked mercilessly by the kref |
| * maintainer, and anyone else who happens to notice it. You have |
| * been warned. |
| * |
| * Subtract @count from the refcount, and if 0, call release(). |
| * Return 1 if the object was removed, otherwise return 0. Beware, if this |
| * function returns 0, you still can not count on the kref from remaining in |
| * memory. Only use the return value if you want to see if the kref is now |
| * gone, not present. |
| */ |
| static inline int kref_sub(struct kref *kref, unsigned int count, |
| void (*release)(struct kref *kref)) |
| { |
| WARN_ON(release == NULL); |
| |
| if (atomic_sub_and_test((int) count, &kref->refcount)) { |
| release(kref); |
| return 1; |
| } |
| return 0; |
| } |
| |
| /** |
| * kref_put - decrement refcount for object. |
| * @kref: object. |
| * @release: pointer to the function that will clean up the object when the |
| * last reference to the object is released. |
| * This pointer is required, and it is not acceptable to pass kfree |
| * in as this function. If the caller does pass kfree to this |
| * function, you will be publicly mocked mercilessly by the kref |
| * maintainer, and anyone else who happens to notice it. You have |
| * been warned. |
| * |
| * Decrement the refcount, and if 0, call release(). |
| * Return 1 if the object was removed, otherwise return 0. Beware, if this |
| * function returns 0, you still can not count on the kref from remaining in |
| * memory. Only use the return value if you want to see if the kref is now |
| * gone, not present. |
| */ |
| static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref)) |
| { |
| return kref_sub(kref, 1, release); |
| } |
| |
| |
| /** |
| * kref_get_unless_zero - Increment refcount for object unless it is zero. |
| * @kref: object. |
| * |
| * Return non-zero if the increment succeeded. Otherwise return 0. |
| * |
| * This function is intended to simplify locking around refcounting for |
| * objects that can be looked up from a lookup structure, and which are |
| * removed from that lookup structure in the object destructor. |
| * Operations on such objects require at least a read lock around |
| * lookup + kref_get, and a write lock around kref_put + remove from lookup |
| * structure. Furthermore, RCU implementations become extremely tricky. |
| * With a lookup followed by a kref_get_unless_zero *with return value check* |
| * locking in the kref_put path can be deferred to the actual removal from |
| * the lookup structure and RCU lookups become trivial. |
| */ |
| static inline int __must_check kref_get_unless_zero(struct kref *kref) |
| { |
| return atomic_add_unless(&kref->refcount, 1, 0); |
| } |
| #endif /* _KREF_H_ */ |