--- 2.4.17rc2aa1/drivers/block/rd.c.~1~	Wed Dec 19 03:01:04 2001
+++ 2.4.17rc2aa1/drivers/block/rd.c	Fri Dec 21 01:39:15 2001
@@ -191,26 +191,44 @@
  *               2000 Transmeta Corp.
  * aops copied from ramfs.
  */
-static int ramdisk_readpage(struct file *file, struct page * page)
+static void ramdisk_updatepage(struct page * page, int need_kmap)
 {
 	if (!Page_Uptodate(page)) {
-		memset(kmap(page), 0, PAGE_CACHE_SIZE);
-		kunmap(page);
+		struct buffer_head *bh = page->buffers;
+		void * address;
+
+		if (need_kmap)
+			kmap(page);
+		address = page_address(page);
+		if (bh) {
+			struct buffer_head *tmp = bh;
+			do {
+				if (!buffer_uptodate(tmp)) {
+					memset(address, 0, tmp->b_size);
+					mark_buffer_uptodate(tmp, 1);
+				}
+				address += tmp->b_size;
+				tmp = tmp->b_this_page;
+			} while (tmp != bh);
+		} else
+			memset(address, 0, PAGE_SIZE);
+		if (need_kmap)
+			kunmap(page);
 		flush_dcache_page(page);
 		SetPageUptodate(page);
 	}
+}
+
+static int ramdisk_readpage(struct file *file, struct page * page)
+{
+	ramdisk_updatepage(page, 1);
 	UnlockPage(page);
 	return 0;
 }
 
 static int ramdisk_prepare_write(struct file *file, struct page *page, unsigned offset, unsigned to)
 {
-	if (!Page_Uptodate(page)) {
-		void *addr = page_address(page);
-		memset(addr, 0, PAGE_CACHE_SIZE);
-		flush_dcache_page(page);
-		SetPageUptodate(page);
-	}
+	ramdisk_updatepage(page, 0);
 	SetPageDirty(page);
 	return 0;
 }
@@ -233,10 +251,18 @@
 	unsigned long index;
 	int offset, size, err;
 
-	err = -EIO;
 	err = 0;
 	mapping = rd_bdev[minor]->bd_inode->i_mapping;
 
+	/* writing a buffer cache not uptodate must not clear it */
+	if (sbh->b_page->mapping == mapping) {
+		if (rw == WRITE) {
+			mark_buffer_uptodate(sbh, 1);
+			SetPageDirty(sbh->b_page);
+		}
+		goto out;
+	}
+
 	index = sbh->b_rsector >> (PAGE_CACHE_SHIFT - 9);
 	offset = (sbh->b_rsector << 9) & ~PAGE_CACHE_MASK;
 	size = sbh->b_size;
@@ -262,11 +288,7 @@
 				goto out;
 			err = 0;
 
-			if (!Page_Uptodate(page)) {
-				memset(kmap(page), 0, PAGE_CACHE_SIZE);
-				kunmap(page);
-				SetPageUptodate(page);
-			}
+			ramdisk_updatepage(page, 1);
 
 			unlock = 1;
 		}