[PATCH] inode_diet: Replace inode.u.generic_ip with inode.i_private

The following patches reduce the size of the VFS inode structure by 28 bytes
on a UP x86.  (It would be more on an x86_64 system).  This is a 10% reduction
in the inode size on a UP kernel that is configured in a production mode
(i.e., with no spinlock or other debugging functions enabled; if you want to
save memory taken up by in-core inodes, the first thing you should do is
disable the debugging options; they are responsible for a huge amount of bloat
in the VFS inode structure).

This patch:

The filesystem or device-specific pointer in the inode is inside a union,
which is pretty pointless given that all 30+ users of this field have been
using the void pointer.  Get rid of the union and rename it to i_private, with
a comment to explain who is allowed to use the void pointer.  This is just a
cleanup, but it allows us to reuse the union 'u' for something something where
the union will actually be used.

[judith@osdl.org: powerpc build fix]
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Judith Lebzelter <judith@osdl.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 4 insertions, 4 deletions

diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index e4b430552c88..bf3901ab1744 100644
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -32,8 +32,8 @@ static ssize_t default_write_file(struct file *file, const char __user *buf,
 
 static int default_open(struct inode *inode, struct file *file)
 {
-        if (inode->u.generic_ip)
-                file->private_data = inode->u.generic_ip;
+        if (inode->i_private)
+                file->private_data = inode->i_private;
 
         return 0;
 }
diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
index 3ca268d2e5a2..717f4821ed02 100644
--- a/fs/debugfs/inode.c
+++ b/fs/debugfs/inode.c
@@ -168,7 +168,7 @@ static int debugfs_create_by_name(const char *name, mode_t mode,
  *          directory dentry if set.  If this paramater is NULL, then the
  *          file will be created in the root of the debugfs filesystem.
  * @data: a pointer to something that the caller will want to get to later
- *        on.  The inode.u.generic_ip pointer will point to this value on
+ *        on.  The inode.i_private pointer will point to this value on
  *        the open() call.
  * @fops: a pointer to a struct file_operations that should be used for
  *        this file.
@@ -209,7 +209,7 @@ struct dentry *debugfs_create_file(const char *name, mode_t mode,
 
         if (dentry->d_inode) {
                 if (data)
-                        dentry->d_inode->u.generic_ip = data;
+                        dentry->d_inode->i_private = data;
                 if (fops)
                         dentry->d_inode->i_fop = fops;
         }