The format of the on-disk mirror logs is architecture-dependent.

The solution seems to be to use to set_le_bit test_le_bit functions that ext2
uses. That makes the BE machines keep the bitmap internally in LE order - it
does mean you can't use any other type of operations on the bitmap words but
that looks to be OK in this instance. The efficiency tradeoff is very minimal as
you would expect for something that ext2 uses.

The nice thing about this way is that there is no on-disk format change for
32bit LE boxes at least, and even nicer is that it removes code and data
structures because log->disk_bits disappears.

From: Patrick Caulfield <pcaulfie@redhat.com>

[Untested]

Index: linux-2.6.14-rc2/drivers/md/dm-log.c
===================================================================
--- linux-2.6.14-rc2.orig/drivers/md/dm-log.c	2005-09-28 18:32:53.000000000 +0100
+++ linux-2.6.14-rc2/drivers/md/dm-log.c	2005-09-28 18:33:30.000000000 +0100
@@ -157,7 +157,6 @@
 	struct log_header *disk_header;
 
 	struct io_region bits_location;
-	uint32_t *disk_bits;
 };
 
 /*
@@ -166,20 +165,20 @@
  */
 static  inline int log_test_bit(uint32_t *bs, unsigned bit)
 {
-	return test_bit(bit, (unsigned long *) bs) ? 1 : 0;
+	return ext2_test_bit(bit, (unsigned long *) bs) ? 1 : 0;
 }
 
 static inline void log_set_bit(struct log_c *l,
 			       uint32_t *bs, unsigned bit)
 {
-	set_bit(bit, (unsigned long *) bs);
+	ext2_set_bit(bit, (unsigned long *) bs);
 	l->touched = 1;
 }
 
 static inline void log_clear_bit(struct log_c *l,
 				 uint32_t *bs, unsigned bit)
 {
-	clear_bit(bit, (unsigned long *) bs);
+	ext2_clear_bit(bit, (unsigned long *) bs);
 	l->touched = 1;
 }
 
@@ -239,45 +238,24 @@
 /*----------------------------------------------------------------
  * Bits IO
  *--------------------------------------------------------------*/
-static inline void bits_to_core(uint32_t *core, uint32_t *disk, unsigned count)
-{
-	unsigned i;
-
-	for (i = 0; i < count; i++)
-		core[i] = le32_to_cpu(disk[i]);
-}
-
-static inline void bits_to_disk(uint32_t *core, uint32_t *disk, unsigned count)
-{
-	unsigned i;
-
-	/* copy across the clean/dirty bitset */
-	for (i = 0; i < count; i++)
-		disk[i] = cpu_to_le32(core[i]);
-}
-
 static int read_bits(struct log_c *log)
 {
 	int r;
 	unsigned long ebits;
 
 	r = dm_io_sync_vm(1, &log->bits_location, READ,
-			  log->disk_bits, &ebits);
+			  log->clean_bits, &ebits);
 	if (r)
 		return r;
 
-	bits_to_core(log->clean_bits, log->disk_bits,
-		     log->bitset_uint32_count);
 	return 0;
 }
 
 static int write_bits(struct log_c *log)
 {
 	unsigned long ebits;
-	bits_to_disk(log->clean_bits, log->disk_bits,
-		     log->bitset_uint32_count);
 	return dm_io_sync_vm(1, &log->bits_location, WRITE,
-			     log->disk_bits, &ebits);
+			     log->clean_bits, &ebits);
 }
 
 /*----------------------------------------------------------------
@@ -433,11 +411,6 @@
 	size = dm_round_up(lc->bitset_uint32_count * sizeof(uint32_t),
 			   1 << SECTOR_SHIFT);
 	lc->bits_location.count = size >> SECTOR_SHIFT;
-	lc->disk_bits = vmalloc(size);
-	if (!lc->disk_bits) {
-		vfree(lc->disk_header);
-		goto bad;
-	}
 	return 0;
 
  bad:
@@ -451,7 +424,6 @@
 	struct log_c *lc = (struct log_c *) log->context;
 	dm_put_device(lc->ti, lc->log_dev);
 	vfree(lc->disk_header);
-	vfree(lc->disk_bits);
 	core_dtr(log);
 }