Replace page_read() with read_kmap_page()/__read_kmap_page().  This probably
fixes behaviour on highmem systems, since page_address() was being used
without kmap().  Also eliminate the need to re-take the page lock during
writes to the page.

Signed-off-by: Nate Diller <nate.diller@gmail.com>

---

diff -urpN -X dontdiff linux-2.6.21-rc5-mm4/drivers/mtd/devices/block2mtd.c linux-2.6.21-rc5-mm4-test/drivers/mtd/devices/block2mtd.c
--- linux-2.6.21-rc5-mm4/drivers/mtd/devices/block2mtd.c	2007-04-05 17:14:24.000000000 -0700
+++ linux-2.6.21-rc5-mm4-test/drivers/mtd/devices/block2mtd.c	2007-04-06 01:59:19.000000000 -0700
@@ -39,12 +39,6 @@ struct block2mtd_dev {
 /* Static info about the MTD, used in cleanup_module */
 static LIST_HEAD(blkmtd_device_list);
 
-
-static struct page *page_read(struct address_space *mapping, int index)
-{
-	return read_mapping_page(mapping, index, NULL);
-}
-
 /* erase a specified part of the device */
 static int _block2mtd_erase(struct block2mtd_dev *dev, loff_t to, size_t len)
 {
@@ -56,23 +50,19 @@ static int _block2mtd_erase(struct block
 	u_long *max;
 
 	while (pages) {
-		page = page_read(mapping, index);
-		if (!page)
-			return -ENOMEM;
+		page = __read_kmap_page(mapping, index);
 		if (IS_ERR(page))
 			return PTR_ERR(page);
 
 		max = page_address(page) + PAGE_SIZE;
 		for (p=page_address(page); p<max; p++)
 			if (*p != -1UL) {
-				lock_page(page);
 				memset(page_address(page), 0xff, PAGE_SIZE);
 				set_page_dirty(page);
-				unlock_page(page);
 				break;
 			}
 
-		page_cache_release(page);
+		put_locked_page(page);
 		pages--;
 		index++;
 	}
@@ -125,14 +115,12 @@ static int block2mtd_read(struct mtd_inf
 			cpylen = len;	// this page
 		len = len - cpylen;
 
-		page = page_read(dev->blkdev->bd_inode->i_mapping, index);
-		if (!page)
-			return -ENOMEM;
+		page = read_kmap_page(dev->blkdev->bd_inode->i_mapping, index);
 		if (IS_ERR(page))
 			return PTR_ERR(page);
 
 		memcpy(buf, page_address(page) + offset, cpylen);
-		page_cache_release(page);
+		put_kmapped_page(page);
 
 		if (retlen)
 			*retlen += cpylen;
@@ -163,19 +151,15 @@ static int _block2mtd_write(struct block
 			cpylen = len;			// this page
 		len = len - cpylen;
 
-		page = page_read(mapping, index);
-		if (!page)
-			return -ENOMEM;
+		page = __read_kmap_page(mapping, index);
 		if (IS_ERR(page))
 			return PTR_ERR(page);
 
 		if (memcmp(page_address(page)+offset, buf, cpylen)) {
-			lock_page(page);
 			memcpy(page_address(page) + offset, buf, cpylen);
 			set_page_dirty(page);
-			unlock_page(page);
 		}
-		page_cache_release(page);
+		put_locked_page(page);
 
 		if (retlen)
 			*retlen += cpylen;
-
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