patch-2.4.5 linux/fs/char_dev.c

• 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);
+	}
+}
+