fs: Remove i_cindex from struct inode

The only user of the i_cindex element in the inode structure is used
is by the firewire drivers.  As part of an attempt to slim down the
inode structure to save memory --- since a typical Linux system will
have hundreds of thousands if not millions of inodes cached, a
reduction in the size inode has high leverage.

The firewire driver does not need i_cindex in any fast path, so it's
simple enough to calculate when it is needed, instead of wasting space
in the inode structure.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: krh@redhat.com
Cc: stefanr@s5r6.in-berlin.de
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

drivers/ieee1394/dv1394.c

@@ -1789,12 +1789,13 @@ static int dv1394_open(struct inode *inode, struct file *file)
 	} else {
 		/* look up the card by ID */
 		unsigned long flags;
+		int idx = ieee1394_file_to_instance(file);
 
 		spin_lock_irqsave(&dv1394_cards_lock, flags);
 		if (!list_empty(&dv1394_cards)) {
 			struct video_card *p;
 			list_for_each_entry(p, &dv1394_cards, list) {
-				if ((p->id) == ieee1394_file_to_instance(file)) {
+				if ((p->id) == idx) {
 					video = p;
 					break;
 				}
@@ -1803,7 +1804,7 @@ static int dv1394_open(struct inode *inode, struct file *file)
 		spin_unlock_irqrestore(&dv1394_cards_lock, flags);
 
 		if (!video) {
-			debug_printk("dv1394: OHCI card %d not found", ieee1394_file_to_instance(file));
+			debug_printk("dv1394: OHCI card %d not found", idx);
 			return -ENODEV;
 		}
 

drivers/ieee1394/ieee1394_core.h

@@ -5,6 +5,7 @@
 #include <linux/fs.h>
 #include <linux/list.h>
 #include <linux/types.h>
+#include <linux/cdev.h>
 #include <asm/atomic.h>
 
 #include "hosts.h"
@@ -155,7 +156,10 @@ void hpsb_packet_received(struct hpsb_host *host, quadlet_t *data, size_t size,
  */
 static inline unsigned char ieee1394_file_to_instance(struct file *file)
 {
-	return file->f_path.dentry->d_inode->i_cindex;
+	int idx = cdev_index(file->f_path.dentry->d_inode);
+	if (idx < 0)
+		idx = 0;
+	return idx;
 }
 
 extern int hpsb_disable_irm;

fs/char_dev.c

@@ -375,7 +375,6 @@ static int chrdev_open(struct inode *inode, struct file *filp)
 		p = inode->i_cdev;
 		if (!p) {
 			inode->i_cdev = p = new;
-			inode->i_cindex = idx;
 			list_add(&inode->i_devices, &p->list);
 			new = NULL;
 		} else if (!cdev_get(p))
@@ -405,6 +404,18 @@ static int chrdev_open(struct inode *inode, struct file *filp)
 	return ret;
 }
 
+int cdev_index(struct inode *inode)
+{
+	int idx;
+	struct kobject *kobj;
+
+	kobj = kobj_lookup(cdev_map, inode->i_rdev, &idx);
+	if (!kobj)
+		return -1;
+	kobject_put(kobj);
+	return idx;
+}
+
 void cd_forget(struct inode *inode)
 {
 	spin_lock(&cdev_lock);
@@ -557,6 +568,7 @@ EXPORT_SYMBOL(cdev_init);
 EXPORT_SYMBOL(cdev_alloc);
 EXPORT_SYMBOL(cdev_del);
 EXPORT_SYMBOL(cdev_add);
+EXPORT_SYMBOL(cdev_index);
 EXPORT_SYMBOL(register_chrdev);
 EXPORT_SYMBOL(unregister_chrdev);
 EXPORT_SYMBOL(directly_mappable_cdev_bdi);

include/linux/cdev.h

@@ -28,6 +28,8 @@ int cdev_add(struct cdev *, dev_t, unsigned);
 
 void cdev_del(struct cdev *);
 
+int cdev_index(struct inode *inode);
+
 void cd_forget(struct inode *);
 
 extern struct backing_dev_info directly_mappable_cdev_bdi;

include/linux/fs.h

@@ -751,7 +751,6 @@ struct inode {
 		struct block_device	*i_bdev;
 		struct cdev		*i_cdev;
 	};
-	int			i_cindex;
 
 	__u32			i_generation;