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

Jeff Dike
2007-07-13T14:39:14Z

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";