[PATCH 2/3] UML - Limit request size on COWed devices

[PATCH 2/3] UML - Limit request size on COWed devices

[Jeff Dike]

COWed devices can't handle more than 32 (64 on x86_64) sectors in one
request due to the size of the bitmap being carried around in the
io_thread_req.

Enforce that by telling the block layer not to put too many sectors in
requests to COWed devices.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
--
 arch/um/drivers/ubd_kern.c |    2 ++
 1 file changed, 2 insertions(+)

Index: linux-2.6.17/arch/um/drivers/ubd_kern.c
===================================================================
--- linux-2.6.17.orig/arch/um/drivers/ubd_kern.c	2007-07-09 08:53:09.000000000 -0400
+++ linux-2.6.17/arch/um/drivers/ubd_kern.c	2007-07-09 18:08:33.000000000 -0400
@@ -712,6 +712,8 @@ static int ubd_add(int n, char **error_o
 	ubd_dev->queue->queuedata = ubd_dev;
 
 	blk_queue_max_hw_segments(ubd_dev->queue, MAX_SG);
+	if(ubd_dev->cow.file != NULL)
+		blk_queue_max_sectors(ubd_dev->queue, 8 * sizeof(long));
 	err = ubd_disk_register(MAJOR_NR, ubd_dev->size, n, &ubd_gendisk[n]);
 	if(err){
 		*error_out = "Failed to register device";

Re: [PATCH 2/3] UML - Limit request size on COWed devices

[Nix]

On 13 Jul 2007, Jeff Dike uttered the following:

> COWed devices can't handle more than 32 (64 on x86_64) sectors in one
> request due to the size of the bitmap being carried around in the
> io_thread_req.

This feels like a -stable candidate to me.

Re: [PATCH 2/3] UML - Limit request size on COWed devices

[Jeff Dike]

On Fri, Jul 13, 2007 at 08:00:13PM +0100, Nix wrote:
> This feels like a -stable candidate to me.

Right you are - that's the first place I sent it.

				Jeff

-- 
Work email - jdike at linux dot intel dot com