minixfs: use offset_in_page()

It's cheaper and more idiomatic than subtracting page_address()
of the corresponding page...

Reviewed-by: Fabio M. De Francesco <fabio.maria.de.francesco@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Author: Al Viro

fs/minix/dir.c

@@ -268,7 +268,7 @@ int minix_add_link(struct dentry *dentry, struct inode *inode)
 	return -EINVAL;
 
 got_it:
-	pos = page_offset(page) + p - (char *)page_address(page);
+	pos = page_offset(page) + offset_in_page(p);
 	err = minix_prepare_chunk(page, pos, sbi->s_dirsize);
 	if (err)
 		goto out_unlock;
@@ -296,8 +296,7 @@ int minix_add_link(struct dentry *dentry, struct inode *inode)
 int minix_delete_entry(struct minix_dir_entry *de, struct page *page)
 {
 	struct inode *inode = page->mapping->host;
-	char *kaddr = page_address(page);
-	loff_t pos = page_offset(page) + (char*)de - kaddr;
+	loff_t pos = page_offset(page) + offset_in_page(de);
 	struct minix_sb_info *sbi = minix_sb(inode->i_sb);
 	unsigned len = sbi->s_dirsize;
 	int err;
@@ -421,8 +420,7 @@ int minix_set_link(struct minix_dir_entry *de, struct page *page,
 {
 	struct inode *dir = page->mapping->host;
 	struct minix_sb_info *sbi = minix_sb(dir->i_sb);
-	loff_t pos = page_offset(page) +
-			(char *)de-(char*)page_address(page);
+	loff_t pos = page_offset(page) + offset_in_page(de);
 	int err;
 
 	lock_page(page);