[PATCH] dev_t [1/3]: kill cdev

Patch from Andries.Brouwer@cwi.nl

Now that 2.5.65 is out, the next dev_t patch.  It was a bit large and
unreadable, so I split it into three clean pieces.  Afterwards, since many
people ask for this, a fourth patch that actually changes the type of dev_t
(not to be applied yet, that is just for playing).

The first patch is the cdev-kill patch that I sent out earlier.  It is no use
having two forms of chardev registration in the source, and my version of the
path of small modifications does not pass through this version, although the
final result will not be that different.  So, kill cdev_cachep,
cdev_cache_init, cdfind, cdget, cdput, inode->i_cdev, struct char_device.
All of this is dead code today.

The second patch removes MAX_CHRDEV.

The third patch polishes linux/major.h.

fs/char_dev.c

@@ -23,110 +23,10 @@
 
 /* serial module kmod load support */
 struct tty_driver *get_tty_driver(kdev_t device);
-#define isa_tty_dev(ma)	(ma == TTY_MAJOR || ma == TTYAUX_MAJOR)
+#define is_a_tty_dev(ma)	(ma == TTY_MAJOR || ma == TTYAUX_MAJOR)
 #define need_serial(ma,mi) (get_tty_driver(mk_kdev(ma,mi)) == NULL)
 #endif
 
-#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));
-}
-
-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);
-	}
-}
-
 struct device_struct {
 	const char * name;
 	struct file_operations * fops;
@@ -144,7 +44,8 @@ int get_chrdev_list(char *page)
 	read_lock(&chrdevs_lock);
 	for (i = 0; i < MAX_CHRDEV ; i++) {
 		if (chrdevs[i].fops) {
-			len += sprintf(page+len, "%3d %s\n", i, chrdevs[i].name);
+			len += sprintf(page+len, "%3d %s\n",
+				       i, chrdevs[i].name);
 		}
 	}
 	read_unlock(&chrdevs_lock);
@@ -152,13 +53,14 @@ int get_chrdev_list(char *page)
 }
 
 /*
-	Return the function table of a device.
-	Load the driver if needed.
-	Increment the reference count of module in question.
-*/
-static struct file_operations * get_chrfops(unsigned int major, unsigned int minor)
+ *	Return the function table of a device.
+ *	Load the driver if needed.
+ *	Increment the reference count of module in question.
+ */
+static struct file_operations *
+get_chrfops(unsigned int major, unsigned int minor)
 {
-	struct file_operations *ret = NULL;
+	struct file_operations *ret;
 
 	if (!major || major >= MAX_CHRDEV)
 		return NULL;
@@ -167,10 +69,12 @@ static struct file_operations * get_chrfops(unsigned int major, unsigned int min
 	ret = fops_get(chrdevs[major].fops);
 	read_unlock(&chrdevs_lock);
 #ifdef CONFIG_KMOD
-	if (ret && isa_tty_dev(major)) {
+	if (ret && is_a_tty_dev(major)) {
 		lock_kernel();
 		if (need_serial(major,minor)) {
 			/* Force request_module anyway, but what for? */
+			/* The reason is that we may have a driver for
+			   /dev/tty1 already, but need one for /dev/ttyS1. */
 			fops_put(ret);
 			ret = NULL;
 		}
@@ -189,7 +93,8 @@ static struct file_operations * get_chrfops(unsigned int major, unsigned int min
 	return ret;
 }
 
-int register_chrdev(unsigned int major, const char * name, struct file_operations *fops)
+int register_chrdev(unsigned int major, const char *name,
+		    struct file_operations *fops)
 {
 	if (major == 0) {
 		write_lock(&chrdevs_lock);

fs/dcache.c

@@ -1563,7 +1563,6 @@ kmem_cache_t *filp_cachep;
 EXPORT_SYMBOL(d_genocide);
 
 extern void bdev_cache_init(void);
-extern void cdev_cache_init(void);
 
 void __init vfs_caches_init(unsigned long mempages)
 {
@@ -1584,5 +1583,4 @@ void __init vfs_caches_init(unsigned long mempages)
 	files_init(mempages); 
 	mnt_init(mempages);
 	bdev_cache_init();
-	cdev_cache_init();
 }

fs/devfs/base.c

@@ -2016,7 +2016,6 @@ static struct inode *_devfs_get_vfs_inode (struct super_block *sb,
     if ( S_ISCHR (de->mode) )
     {
 	inode->i_rdev = to_kdev_t(de->u.cdev.dev);
-	inode->i_cdev = cdget(de->u.cdev.dev);
     }
     else if ( S_ISBLK (de->mode) )
     {

fs/inode.c

@@ -128,7 +128,6 @@ static struct inode *alloc_inode(struct super_block *sb)
 		memset(&inode->i_dquot, 0, sizeof(inode->i_dquot));
 		inode->i_pipe = NULL;
 		inode->i_bdev = NULL;
-		inode->i_cdev = NULL;
 		inode->i_rdev = to_kdev_t(0);
 		inode->i_security = NULL;
 		if (security_inode_alloc(inode)) {
@@ -242,10 +241,6 @@ void clear_inode(struct inode *inode)
 		inode->i_sb->s_op->clear_inode(inode);
 	if (inode->i_bdev)
 		bd_forget(inode);
-	else if (inode->i_cdev) {
-		cdput(inode->i_cdev);
-		inode->i_cdev = NULL;
-	}
 	inode->i_state = I_CLEAR;
 }
 
@@ -1315,7 +1310,6 @@ void init_special_inode(struct inode *inode, umode_t mode, dev_t rdev)
 	if (S_ISCHR(mode)) {
 		inode->i_fop = &def_chr_fops;
 		inode->i_rdev = to_kdev_t(rdev);
-		inode->i_cdev = cdget(rdev);
 	} else if (S_ISBLK(mode)) {
 		inode->i_fop = &def_blk_fops;
 		inode->i_rdev = to_kdev_t(rdev);
@@ -1324,5 +1318,6 @@ void init_special_inode(struct inode *inode, umode_t mode, dev_t rdev)
 	else if (S_ISSOCK(mode))
 		inode->i_fop = &bad_sock_fops;
 	else
-		printk(KERN_DEBUG "init_special_inode: bogus i_mode (%o)\n", mode);
+		printk(KERN_DEBUG "init_special_inode: bogus i_mode (%o)\n",
+		       mode);
 }

include/linux/fs.h

@@ -331,12 +331,6 @@ struct address_space {
 	struct address_space	*assoc_mapping;	/* ditto */
 };
 
-struct char_device {
-	struct list_head	hash;
-	atomic_t		count;
-	dev_t			dev;
-};
-
 struct block_device {
 	struct list_head	bd_hash;
 	atomic_t		bd_count;
@@ -388,7 +382,6 @@ struct inode {
 	struct list_head	i_devices;
 	struct pipe_inode_info	*i_pipe;
 	struct block_device	*i_bdev;
-	struct char_device	*i_cdev;
 
 	unsigned long		i_dnotify_mask; /* Directory notify events */
 	struct dnotify_struct	*i_dnotify; /* for directory notifications */
@@ -1046,8 +1039,6 @@ extern struct block_device *bdget(dev_t);
 extern int bd_acquire(struct inode *inode);
 extern void bd_forget(struct inode *inode);
 extern void bdput(struct block_device *);
-extern struct char_device *cdget(dev_t);
-extern void cdput(struct char_device *);
 extern int blkdev_open(struct inode *, struct file *);
 extern int blkdev_close(struct inode *, struct file *);
 extern struct file_operations def_blk_fops;

kernel/ksyms.c

@@ -203,8 +203,6 @@ EXPORT_SYMBOL(notify_change);
 EXPORT_SYMBOL(set_blocksize);
 EXPORT_SYMBOL(sb_set_blocksize);
 EXPORT_SYMBOL(sb_min_blocksize);
-EXPORT_SYMBOL(cdget);
-EXPORT_SYMBOL(cdput);
 EXPORT_SYMBOL(bdget);
 EXPORT_SYMBOL(bdput);
 EXPORT_SYMBOL(bd_claim);