[JFFS2] Core changes required to support JFFS2-on-Dataflash devices.

DataFlash page-sizes are not a power of two (they're multiples of 528
bytes).  There are a few places in JFFS2 code where sector_size is used
as a bitmask.  A new macro (SECTOR_ADDR) was defined to calculate these
sector addresses. For non-DataFlash devices, the original (faster)
bitmask operation is still used.

In scan.c, the EMPTY_SCAN_SIZE was a constant of 1024.
Since this could be larger than the sector size of the DataFlash, this
is now basically set to MIN(sector_size, 1024).

Addition of a jffs2_is_writebuffered() macro.

Signed-off-by: Andrew Victor <andrew@sanpeople.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/fs/jffs2/gc.c b/fs/jffs2/gc.c
index 87ec74f..61ae001 100644
--- a/fs/jffs2/gc.c
+++ b/fs/jffs2/gc.c
@@ -7,7 +7,7 @@
  *
  * For licensing information, see the file 'LICENCE' in this directory.
  *
- * $Id: gc.c,v 1.144 2004/12/21 11:18:50 dwmw2 Exp $
+ * $Id: gc.c,v 1.145 2005/02/09 09:09:01 pavlov Exp $
  *
  */
 
@@ -816,8 +816,7 @@
 
 			/* Doesn't matter if there's one in the same erase block. We're going to 
 			   delete it too at the same time. */
-			if ((raw->flash_offset & ~(c->sector_size-1)) ==
-			    (fd->raw->flash_offset & ~(c->sector_size-1)))
+			if (SECTOR_ADDR(raw->flash_offset) == SECTOR_ADDR(fd->raw->flash_offset))
 				continue;
 
 			D1(printk(KERN_DEBUG "Check potential deletion dirent at %08x\n", ref_offset(raw)));