Variable Order Page Cache: Fixup fallback functions

Fixup the fallback function in fs/libfs.c to be able to handle
higher order page cache pages.

Signed-off-by: Christoph Lameter <clameter@sgi.com>

---
 fs/libfs.c |   16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

Index: linux-2.6.21-rc7/fs/libfs.c
===================================================================
--- linux-2.6.21-rc7.orig/fs/libfs.c	2007-04-18 21:52:49.000000000 -0700
+++ linux-2.6.21-rc7/fs/libfs.c	2007-04-18 21:54:51.000000000 -0700
@@ -320,8 +320,8 @@ int simple_rename(struct inode *old_dir,
 
 int simple_readpage(struct file *file, struct page *page)
 {
-	clear_highpage(page);
-	flush_dcache_page(page);
+	clear_mapping_page(file->f_mapping, page);
+	flush_mapping_page(file->f_mapping, page);
 	SetPageUptodate(page);
 	unlock_page(page);
 	return 0;
@@ -331,11 +331,15 @@ int simple_prepare_write(struct file *fi
 			unsigned from, unsigned to)
 {
 	if (!PageUptodate(page)) {
-		if (to - from != PAGE_CACHE_SIZE) {
+		if (to - from != page_cache_size(file->f_mapping)) {
+			/*
+			 * Mapping to higher order pages need to be supported
+			 * if higher order pages can be in highmem
+			 */
 			void *kaddr = kmap_atomic(page, KM_USER0);
 			memset(kaddr, 0, from);
-			memset(kaddr + to, 0, PAGE_CACHE_SIZE - to);
-			flush_dcache_page(page);
+			memset(kaddr + to, 0, page_cache_size(file->f_mapping) - to);
+			flush_mapping_page(file->f_mapping, page);
 			kunmap_atomic(kaddr, KM_USER0);
 		}
 	}
@@ -346,7 +350,7 @@ int simple_commit_write(struct file *fil
 			unsigned from, unsigned to)
 {
 	struct inode *inode = page->mapping->host;
-	loff_t pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;
+	loff_t pos = ((loff_t)page->index << page_cache_shift(file->f_mapping)) + to;
 
 	if (!PageUptodate(page))
 		SetPageUptodate(page);