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>

5 files changed, 23 insertions, 5 deletions

diff --git a/drivers/ieee1394/dv1394.c b/drivers/ieee1394/dv1394.c
index 823a6297a1af..2cd00b5b45b4 100644
--- a/drivers/ieee1394/dv1394.c
+++ b/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;
                 }
 
diff --git a/drivers/ieee1394/ieee1394_core.h b/drivers/ieee1394/ieee1394_core.h
index 21d50f73a210..28b9f58bafd2 100644
--- a/drivers/ieee1394/ieee1394_core.h
+++ b/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;
diff --git a/fs/char_dev.c b/fs/char_dev.c
index 38f71222a552..b7c9d5187a75 100644
--- a/fs/char_dev.c
+++ b/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);
diff --git a/include/linux/cdev.h b/include/linux/cdev.h
index fb4591977b03..f389e319a454 100644
--- a/include/linux/cdev.h
+++ b/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;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index e7833ef5d1d6..bcd63706db87 100644
--- a/include/linux/fs.h
+++ b/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;