[GFS2] inode_diet: Replace inode.u.generic_ip with inode.i_private (gfs)

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.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: Steven Whitehouse <swhiteho@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>

fs/dlm/debug_fs.c

@@ -282,7 +282,7 @@ static int rsb_open(struct inode *inode, struct file *file)
 		return ret;
 
 	seq = file->private_data;
-	seq->private = inode->u.generic_ip;
+	seq->private = inode->i_private;
 
 	return 0;
 }
@@ -301,7 +301,7 @@ static struct file_operations rsb_fops = {
 
 static int waiters_open(struct inode *inode, struct file *file)
 {
-	file->private_data = inode->u.generic_ip;
+	file->private_data = inode->i_private;
 	return 0;
 }
 

fs/gfs2/inode.c

@@ -160,7 +160,7 @@ struct inode *gfs2_inode_lookup(struct super_block *sb, struct gfs2_inum *inum,
 	if (inode->i_state & I_NEW) {
 		struct gfs2_sbd *sdp = GFS2_SB(inode);
 		umode_t mode = DT2IF(type);
-		inode->u.generic_ip = ip;
+		inode->i_private = ip;
 		inode->i_mode = mode;
 
 		if (S_ISREG(mode)) {

fs/gfs2/meta_io.c

@@ -78,7 +78,7 @@ struct inode *gfs2_aspace_get(struct gfs2_sbd *sdp)
 		mapping_set_gfp_mask(aspace->i_mapping, GFP_NOFS);
 		aspace->i_mapping->a_ops = &aspace_aops;
 		aspace->i_size = ~0ULL;
-		aspace->u.generic_ip = NULL;
+		aspace->i_private = NULL;
 		insert_inode_hash(aspace);
 	}
 	return aspace;

fs/gfs2/ops_super.c

@@ -53,7 +53,7 @@ static int gfs2_write_inode(struct inode *inode, int sync)
 	struct gfs2_inode *ip = GFS2_I(inode);
 
 	/* Check this is a "normal" inode */
-	if (inode->u.generic_ip) {
+	if (inode->i_private) {
 		if (current->flags & PF_MEMALLOC)
 			return 0;
 		if (sync)
@@ -280,7 +280,7 @@ static void gfs2_clear_inode(struct inode *inode)
 	 * serves to contain an address space (see rgrp.c, meta_io.c)
 	 * which therefore doesn't have its own glocks.
 	 */
-	if (inode->u.generic_ip) {
+	if (inode->i_private) {
 		struct gfs2_inode *ip = GFS2_I(inode);
 		gfs2_glock_inode_squish(inode);
 		gfs2_assert(inode->i_sb->s_fs_info, ip->i_gl->gl_state == LM_ST_UNLOCKED);
@@ -381,7 +381,7 @@ static void gfs2_delete_inode(struct inode *inode)
 	struct gfs2_holder gh;
 	int error;
 
-	if (!inode->u.generic_ip)
+	if (!inode->i_private)
 		goto out;
 
 	error = gfs2_glock_nq_init(ip->i_gl, LM_ST_EXCLUSIVE, LM_FLAG_TRY_1CB | GL_NOCACHE, &gh);