1 /*
2 * linux/fs/block_dev.c
3 *
4 * Copyright (C) 1991, 1992 Linus Torvalds
5 */
6
7 #include <linux/config.h>
8 #include <linux/init.h>
9 #include <linux/slab.h>
10
11 #define HASH_BITS 6
12 #define HASH_SIZE (1UL << HASH_BITS)
13 #define HASH_MASK (HASH_SIZE-1)
14 static struct list_head cdev_hashtable[HASH_SIZE];
15 static spinlock_t cdev_lock = SPIN_LOCK_UNLOCKED;
16 static kmem_cache_t * cdev_cachep;
17
18 #define alloc_cdev() \
19 ((struct char_device *) kmem_cache_alloc(cdev_cachep, SLAB_KERNEL))
20 #define destroy_cdev(cdev) kmem_cache_free(cdev_cachep, (cdev))
21
init_once(void * foo,kmem_cache_t * cachep,unsigned long flags)22 static void init_once(void * foo, kmem_cache_t * cachep, unsigned long flags)
23 {
24 struct char_device * cdev = (struct char_device *) foo;
25
26 if ((flags & (SLAB_CTOR_VERIFY|SLAB_CTOR_CONSTRUCTOR)) ==
27 SLAB_CTOR_CONSTRUCTOR)
28 {
29 memset(cdev, 0, sizeof(*cdev));
30 sema_init(&cdev->sem, 1);
31 }
32 }
33
cdev_cache_init(void)34 void __init cdev_cache_init(void)
35 {
36 int i;
37 struct list_head *head = cdev_hashtable;
38
39 i = HASH_SIZE;
40 do {
41 INIT_LIST_HEAD(head);
42 head++;
43 i--;
44 } while (i);
45
46 cdev_cachep = kmem_cache_create("cdev_cache",
47 sizeof(struct char_device),
48 0, SLAB_HWCACHE_ALIGN, init_once,
49 NULL);
50 if (!cdev_cachep)
51 panic("Cannot create cdev_cache SLAB cache");
52 }
53
54 /*
55 * Most likely _very_ bad one - but then it's hardly critical for small
56 * /dev and can be fixed when somebody will need really large one.
57 */
hash(dev_t dev)58 static inline unsigned long hash(dev_t dev)
59 {
60 unsigned long tmp = dev;
61 tmp = tmp + (tmp >> HASH_BITS) + (tmp >> HASH_BITS*2);
62 return tmp & HASH_MASK;
63 }
64
cdfind(dev_t dev,struct list_head * head)65 static struct char_device *cdfind(dev_t dev, struct list_head *head)
66 {
67 struct list_head *p;
68 struct char_device *cdev;
69 for (p=head->next; p!=head; p=p->next) {
70 cdev = list_entry(p, struct char_device, hash);
71 if (cdev->dev != dev)
72 continue;
73 atomic_inc(&cdev->count);
74 return cdev;
75 }
76 return NULL;
77 }
78
cdget(dev_t dev)79 struct char_device *cdget(dev_t dev)
80 {
81 struct list_head * head = cdev_hashtable + hash(dev);
82 struct char_device *cdev, *new_cdev;
83 spin_lock(&cdev_lock);
84 cdev = cdfind(dev, head);
85 spin_unlock(&cdev_lock);
86 if (cdev)
87 return cdev;
88 new_cdev = alloc_cdev();
89 if (!new_cdev)
90 return NULL;
91 atomic_set(&new_cdev->count,1);
92 new_cdev->dev = dev;
93 spin_lock(&cdev_lock);
94 cdev = cdfind(dev, head);
95 if (!cdev) {
96 list_add(&new_cdev->hash, head);
97 spin_unlock(&cdev_lock);
98 return new_cdev;
99 }
100 spin_unlock(&cdev_lock);
101 destroy_cdev(new_cdev);
102 return cdev;
103 }
104
cdput(struct char_device * cdev)105 void cdput(struct char_device *cdev)
106 {
107 if (atomic_dec_and_lock(&cdev->count, &cdev_lock)) {
108 list_del(&cdev->hash);
109 spin_unlock(&cdev_lock);
110 destroy_cdev(cdev);
111 }
112 }
113
114