Viewing file:  char_dev.c (2.5 KB) -rw-r--r--
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/*
* linux/fs/block_dev.c
*
* Copyright (C) 1991, 1992 Linus Torvalds
*/
#include <linux/config.h>
#include <linux/init.h>
#include <linux/slab.h>
#define HASH_BITS 6
#define HASH_SIZE (1UL << HASH_BITS)
#define HASH_MASK (HASH_SIZE-1)
static struct list_head cdev_hashtable[HASH_SIZE];
static spinlock_t cdev_lock = SPIN_LOCK_UNLOCKED;
static kmem_cache_t * cdev_cachep;
#define alloc_cdev() \
((struct char_device *) kmem_cache_alloc(cdev_cachep, SLAB_KERNEL))
#define destroy_cdev(cdev) kmem_cache_free(cdev_cachep, (cdev))
static void init_once(void * foo, kmem_cache_t * cachep, unsigned long flags)
{
struct char_device * cdev = (struct char_device *) foo;
if ((flags & (SLAB_CTOR_VERIFY|SLAB_CTOR_CONSTRUCTOR)) ==
SLAB_CTOR_CONSTRUCTOR)
{
memset(cdev, 0, sizeof(*cdev));
sema_init(&cdev->sem, 1);
}
}
void __init cdev_cache_init(void)
{
int i;
struct list_head *head = cdev_hashtable;
i = HASH_SIZE;
do {
INIT_LIST_HEAD(head);
head++;
i--;
} while (i);
cdev_cachep = kmem_cache_create("cdev_cache",
sizeof(struct char_device),
0, SLAB_HWCACHE_ALIGN, init_once,
NULL);
if (!cdev_cachep)
panic("Cannot create cdev_cache SLAB cache");
}
/*
* Most likely _very_ bad one - but then it's hardly critical for small
* /dev and can be fixed when somebody will need really large one.
*/
static inline unsigned long hash(dev_t dev)
{
unsigned long tmp = dev;
tmp = tmp + (tmp >> HASH_BITS) + (tmp >> HASH_BITS*2);
return tmp & HASH_MASK;
}
static struct char_device *cdfind(dev_t dev, struct list_head *head)
{
struct list_head *p;
struct char_device *cdev;
for (p=head->next; p!=head; p=p->next) {
cdev = list_entry(p, struct char_device, hash);
if (cdev->dev != dev)
continue;
atomic_inc(&cdev->count);
return cdev;
}
return NULL;
}
struct char_device *cdget(dev_t dev)
{
struct list_head * head = cdev_hashtable + hash(dev);
struct char_device *cdev, *new_cdev;
spin_lock(&cdev_lock);
cdev = cdfind(dev, head);
spin_unlock(&cdev_lock);
if (cdev)
return cdev;
new_cdev = alloc_cdev();
if (!new_cdev)
return NULL;
atomic_set(&new_cdev->count,1);
new_cdev->dev = dev;
spin_lock(&cdev_lock);
cdev = cdfind(dev, head);
if (!cdev) {
list_add(&new_cdev->hash, head);
spin_unlock(&cdev_lock);
return new_cdev;
}
spin_unlock(&cdev_lock);
destroy_cdev(new_cdev);
return cdev;
}
void cdput(struct char_device *cdev)
{
if (atomic_dec_and_lock(&cdev->count, &cdev_lock)) {
list_del(&cdev->hash);
spin_unlock(&cdev_lock);
destroy_cdev(cdev);
}
}
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