| /* |
| * linux/fs/block_dev.c |
| * |
| * Copyright (C) 1991, 1992 Linus Torvalds |
| */ |
| |
| #include <linux/config.h> |
| #include <linux/init.h> |
| #include <linux/fs.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; |
| list_for_each(p, head) { |
| 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); |
| } |
| } |
| |