1 /* 2 * kref.h - library routines for handling generic reference counted objects 3 * 4 * Copyright (C) 2004 Greg Kroah-Hartman <[email protected]> 5 * Copyright (C) 2004 IBM Corp. 6 * 7 * based on kobject.h which was: 8 * Copyright (C) 2002-2003 Patrick Mochel <[email protected]> 9 * Copyright (C) 2002-2003 Open Source Development Labs 10 * 11 * This file is released under the GPLv2. 12 * 13 */ 14 15 #ifndef _KREF_H_ 16 #define _KREF_H_ 17 18 #include <linux/bug.h> 19 #include <linux/atomic.h> 20 #include <linux/kernel.h> 21 22 struct kref { 23 atomic_t refcount; 24 }; 25 26 /** 27 * kref_init - initialize object. 28 * @kref: object in question. 29 */ 30 static inline void kref_init(struct kref *kref) 31 { 32 atomic_set(&kref->refcount, 1); 33 } 34 35 /** 36 * kref_get - increment refcount for object. 37 * @kref: object. 38 */ 39 static inline void kref_get(struct kref *kref) 40 { 41 WARN_ON(!atomic_read(&kref->refcount)); 42 atomic_inc(&kref->refcount); 43 } 44 45 /** 46 * kref_sub - subtract a number of refcounts for object. 47 * @kref: object. 48 * @count: Number of recounts to subtract. 49 * @release: pointer to the function that will clean up the object when the 50 * last reference to the object is released. 51 * This pointer is required, and it is not acceptable to pass kfree 52 * in as this function. If the caller does pass kfree to this 53 * function, you will be publicly mocked mercilessly by the kref 54 * maintainer, and anyone else who happens to notice it. You have 55 * been warned. 56 * 57 * Subtract @count from the refcount, and if 0, call release(). 58 * Return 1 if the object was removed, otherwise return 0. Beware, if this 59 * function returns 0, you still can not count on the kref from remaining in 60 * memory. Only use the return value if you want to see if the kref is now 61 * gone, not present. 62 */ 63 static inline int kref_sub(struct kref *kref, unsigned int count, 64 void (*release)(struct kref *kref)) 65 { 66 WARN_ON(release == NULL); 67 68 if (atomic_sub_and_test((int) count, &kref->refcount)) { 69 release(kref); 70 return 1; 71 } 72 return 0; 73 } 74 75 /** 76 * kref_put - decrement refcount for object. 77 * @kref: object. 78 * @release: pointer to the function that will clean up the object when the 79 * last reference to the object is released. 80 * This pointer is required, and it is not acceptable to pass kfree 81 * in as this function. If the caller does pass kfree to this 82 * function, you will be publicly mocked mercilessly by the kref 83 * maintainer, and anyone else who happens to notice it. You have 84 * been warned. 85 * 86 * Decrement the refcount, and if 0, call release(). 87 * Return 1 if the object was removed, otherwise return 0. Beware, if this 88 * function returns 0, you still can not count on the kref from remaining in 89 * memory. Only use the return value if you want to see if the kref is now 90 * gone, not present. 91 */ 92 static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref)) 93 { 94 return kref_sub(kref, 1, release); 95 } 96 #endif /* _KREF_H_ */ 97