[PATCH] small fixes in buffer.c

- Fix the fix to the fix to the sector_t printing in buffer_io_error()

- A few microoptimisations in buffer.c.  Replace:

	set_buffer_foo(bh);

  with

	if (!buffer_foo(bh))
		set_buffer_foo(bh);

  when buffer_fooness is likely.  To avoid the buslocked rmw, and to
  avoid dirtying a cacheline.


- export write_mapping_buffers() - filesystems which put buffers on
  mapping->private_list need this function for I/O scheduling reasons.

fs/buffer.c

@@ -167,8 +167,9 @@ __clear_page_buffers(struct page *page)
 
 static void buffer_io_error(struct buffer_head *bh)
 {
-	printk(KERN_ERR "Buffer I/O error on device %s, logical block %Ld\n",
-			bdevname(bh->b_bdev), (u64)bh->b_blocknr);
+	printk(KERN_ERR "Buffer I/O error on device %s, logical block %Lu\n",
+			bdevname(bh->b_bdev),
+			(unsigned long long)bh->b_blocknr);
 }
 
 /*
@@ -835,6 +836,7 @@ int write_mapping_buffers(struct address_space *mapping)
 out:
 	return ret;
 }
+EXPORT_SYMBOL(write_mapping_buffers);
 
 void mark_buffer_dirty_inode(struct buffer_head *bh, struct inode *inode)
 {
@@ -1400,7 +1402,6 @@ void create_empty_buffers(struct page *page,
 	head = create_buffers(page, blocksize, 1);
 	bh = head;
 	do {
-		bh->b_end_io = NULL;
 		bh->b_state |= b_state;
 		tail = bh;
 		bh = bh->b_this_page;
@@ -1666,10 +1667,13 @@ static int __block_prepare_write(struct inode *inode, struct page *page,
 	    block++, block_start=block_end, bh = bh->b_this_page) {
 		block_end = block_start + blocksize;
 		if (block_end <= from || block_start >= to) {
-			if (PageUptodate(page))
+			if (PageUptodate(page)) {
+				if (!buffer_uptodate(bh))
 					set_buffer_uptodate(bh);
+			}
 			continue;
 		}
+		if (buffer_new(bh))
 			clear_buffer_new(bh);
 		if (!buffer_mapped(bh)) {
 			err = get_block(inode, block, bh, 1);
@@ -1695,6 +1699,7 @@ static int __block_prepare_write(struct inode *inode, struct page *page,
 			}
 		}
 		if (PageUptodate(page)) {
+			if (!buffer_uptodate(bh))
 				set_buffer_uptodate(bh);
 			continue; 
 		}

mm/page-writeback.c

@@ -50,7 +50,7 @@ static int dirty_async_ratio = 50;
  */
 static int dirty_sync_ratio = 60;
 
-static void background_writeout(unsigned long unused);
+static void background_writeout(unsigned long _min_pages);
 
 /*
  * balance_dirty_pages() must be called by processes which are
@@ -492,6 +492,9 @@ int __set_page_dirty_buffers(struct page *page)
 		goto out;
 	}
 
+	if (!PageUptodate(page))
+		buffer_error();
+
 	spin_lock(&mapping->private_lock);
 
 	if (page_has_buffers(page) && !PageSwapCache(page)) {