Date:	Thu, 5 Apr 2001 16:38:18 +0200
From:	Jens Axboe <axboe@suse.de>
To:	Herbert Valerio Riedel <hvr@hvrlab.org>
Subject: Re: /dev/loop0 over lvm... leading to d-state :-(


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On Thu, Apr 05 2001, Jens Axboe wrote:
> On Wed, Apr 04 2001, Herbert Valerio Riedel wrote:
> > 
> > fyi, loop devices over lvm LV's dont work for me...
> > 
> > I've tested with 2.4.3final (and some other 2.4.3 derivates) and two
> > lvm'ized partitions with a size of about 1gig each; mke2fs
> > just goes into D-state and stays there when applying it to /dev/loop0,
> > running it directly on the LV-device works...
> 
> this would appear to be an lvm bug, could you try this patch? it's
> untested, let me know if it doesn't work and I'll try and reproduce
> here.

What do you know, there was one more in there. Even visible in
the original hunk :-). And this time it wasn't a loop bug (the
crowd goes bezerk).

To the LVM folks: you can't use b_dev or b_blocknr inside your
make_request_fn, it destroys stacking drivers such as loop. And
is just plain wrong in the general case too.

-- 
Jens Axboe


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--- /opt/kernel/linux-2.4.3/drivers/md/lvm.c	Mon Jan 29 01:11:20 2001
+++ drivers/md/lvm.c	Thu Apr  5 16:20:12 2001
@@ -148,6 +148,8 @@
  *                 procfs is always supported now. (JT)
  *    12/01/2001 - avoided flushing logical volume in case of shrinking
  *                 because of unecessary overhead in case of heavy updates
+ *    05/04/2001 - don't use b_blocknr/b_dev in lvm_map, it destroys
+ *		   stacking devices (Jens Axboe)
  *
  */
 
@@ -1480,14 +1482,14 @@
  */
 static int lvm_map(struct buffer_head *bh, int rw)
 {
-	int minor = MINOR(bh->b_dev);
+	int minor = MINOR(bh->b_rdev);
 	int ret = 0;
 	ulong index;
 	ulong pe_start;
 	ulong size = bh->b_size >> 9;
-	ulong rsector_tmp = bh->b_blocknr * size;
+	ulong rsector_tmp = bh->b_rsector;
 	ulong rsector_sav;
-	kdev_t rdev_tmp = bh->b_dev;
+	kdev_t rdev_tmp = bh->b_rdev;
 	kdev_t rdev_sav;
 	vg_t *vg_this = vg[VG_BLK(minor)];
 	lv_t *lv = vg_this->lv[LV_BLK(minor)];

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