patch-2.4.5 linux/fs/char_dev.c
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- Lines: 115
- Date:
Tue May 22 09:35:42 2001
- Orig file:
v2.4.4/linux/fs/char_dev.c
- Orig date:
Wed Dec 31 16:00:00 1969
diff -u --recursive --new-file v2.4.4/linux/fs/char_dev.c linux/fs/char_dev.c
@@ -0,0 +1,114 @@
+/*
+ * 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_test(&cdev->count)) {
+ spin_lock(&cdev_lock);
+ list_del(&cdev->hash);
+ spin_unlock(&cdev_lock);
+ destroy_cdev(cdev);
+ }
+}
+
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