1/* 2 * kref.c - library routines for handling generic reference counted objects 3 * 4 * Copyright (C) 2004 Greg Kroah-Hartman <greg@kroah.com> 5 * Copyright (C) 2004 IBM Corp. 6 * 7 * based on lib/kobject.c which was: 8 * Copyright (C) 2002-2003 Patrick Mochel <mochel@osdl.org> 9 * 10 * This file is released under the GPLv2. 11 * 12 */ 13 14#include <linux/kref.h> 15#include <linux/module.h> 16#include <linux/slab.h> 17 18/** 19 * kref_init - initialize object. 20 * @kref: object in question. 21 */ 22void kref_init(struct kref *kref) 23{ 24 atomic_set(&kref->refcount, 1); 25 smp_mb(); 26} 27 28/** 29 * kref_get - increment refcount for object. 30 * @kref: object. 31 */ 32void kref_get(struct kref *kref) 33{ 34 WARN_ON(!atomic_read(&kref->refcount)); 35 atomic_inc(&kref->refcount); 36 smp_mb__after_atomic_inc(); 37} 38 39/** 40 * kref_put - decrement refcount for object. 41 * @kref: object. 42 * @release: pointer to the function that will clean up the object when the 43 * last reference to the object is released. 44 * This pointer is required, and it is not acceptable to pass kfree 45 * in as this function. 46 * 47 * Decrement the refcount, and if 0, call release(). 48 * Return 1 if the object was removed, otherwise return 0. Beware, if this 49 * function returns 0, you still can not count on the kref from remaining in 50 * memory. Only use the return value if you want to see if the kref is now 51 * gone, not present. 52 */ 53int kref_put(struct kref *kref, void (*release)(struct kref *kref)) 54{ 55 WARN_ON(release == NULL); 56 WARN_ON(release == (void (*)(struct kref *))kfree); 57 58 if (atomic_dec_and_test(&kref->refcount)) { 59 release(kref); 60 return 1; 61 } 62 return 0; 63} 64 65 66/** 67 * kref_sub - subtract a number of refcounts for object. 68 * @kref: object. 69 * @count: Number of recounts to subtract. 70 * @release: pointer to the function that will clean up the object when the 71 * last reference to the object is released. 72 * This pointer is required, and it is not acceptable to pass kfree 73 * in as this function. 74 * 75 * Subtract @count from the refcount, and if 0, call release(). 76 * Return 1 if the object was removed, otherwise return 0. Beware, if this 77 * function returns 0, you still can not count on the kref from remaining in 78 * memory. Only use the return value if you want to see if the kref is now 79 * gone, not present. 80 */ 81int kref_sub(struct kref *kref, unsigned int count, 82 void (*release)(struct kref *kref)) 83{ 84 WARN_ON(release == NULL); 85 WARN_ON(release == (void (*)(struct kref *))kfree); 86 87 if (atomic_sub_and_test((int) count, &kref->refcount)) { 88 release(kref); 89 return 1; 90 } 91 return 0; 92} 93 94EXPORT_SYMBOL(kref_init); 95EXPORT_SYMBOL(kref_get); 96EXPORT_SYMBOL(kref_put); 97EXPORT_SYMBOL(kref_sub); 98