[BUG/PATCH] md bitmap broken on big endian machines

[Paul Clements <paul.clements@steeleye.com>]

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Neil,

We just discovered this problem on a 64-bit IBM POWER (ppc64) system. 
The symptom was this BUG():

Sep 20 20:55:51 caspian kernel: kernel BUG in sync_request at 
drivers/md/raid1.c
:1743!
Sep 20 20:55:51 caspian kernel: Oops: Exception in kernel mode, sig: 5 [#1]
Sep 20 20:55:51 caspian kernel: SMP NR_CPUS=128 NUMA PSERIES LPAR
Sep 20 20:55:51 caspian kernel: Modules linked in: nbd raid1 ipv6 nfs 
lockd nfs_
acl sunrpc apparmor aamatch_pcre loop dm_mod e1000 ide_cd cdrom lpfc 
scsi_transp
ort_fc pdc202xx_new sg st ipr firmware_class sd_mod scsi_mod


I traced the problem back to a bad value in bitmap->chunkshift (the 
value was 8, instead of 16, with a chunksize of 64K). I think this means 
that bitmaps are broken on all big endian systems. It looks like we 
should be using ffs instead of find_first_bit. Patch has been compile 
tested only.

Thanks,
Paul

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--- ./drivers/md/bitmap.c.orig	2006-09-21 16:10:17.000000000 -0400
+++ ./drivers/md/bitmap.c	2006-09-21 16:12:16.000000000 -0400
@@ -1578,8 +1578,7 @@ int bitmap_create(mddev_t *mddev)
 	if (err)
 		goto error;
 
-	bitmap->chunkshift = find_first_bit(&bitmap->chunksize,
-					sizeof(bitmap->chunksize));
+	bitmap->chunkshift = ffs(bitmap->chunksize) - 1;
 
 	/* now that chunksize and chunkshift are set, we can use these macros */
  	chunks = (blocks + CHUNK_BLOCK_RATIO(bitmap) - 1) /