[PATCH] Re: loop device changes the block size and causes misaligned accesses to the real device, which can't be processed

[Ben Slusky <sluskyb@paranoiacs.org>]

On Wed, 07 Jan 2004 18:03:48 +0100, Ruben Garcia wrote:
> The loop device advertises a block size of 1024 even when configured 
> over a cdrom.
> 
> When burning a ext2 on a cd, and mounting it directly, I get:
> 
> blocksize=2048;
> 
> when I losetup /dev/loop0 /dev/cdrom, and then try to mount, I get:
> 
> blocksize=1024; and then misaligned transfer; this results in not being 
> able to read the superblock.
> 
> The loop device should be changed to export the same blocksize of the 
> underlying device

Huh, if you look at loop.c it appears to do that already (line 735) but
it doesn't. This patch makes it so.

--- linux-2.6.0/drivers/block/loop.c-orig	2004-01-07 22:47:37.755375858 -0500
+++ linux-2.6.0/drivers/block/loop.c	2004-01-07 22:48:04.990990082 -0500
@@ -732,8 +732,6 @@
 	mapping_set_gfp_mask(inode->i_mapping,
 			     lo->old_gfp_mask & ~(__GFP_IO|__GFP_FS));
 
-	set_blocksize(bdev, lo_blocksize);
-
 	lo->lo_bio = lo->lo_biotail = NULL;
 
 	/*
@@ -749,6 +747,7 @@
 	if (S_ISBLK(inode->i_mode)) {
 		request_queue_t *q = bdev_get_queue(lo_device);
 
+		blk_queue_hardsect_size(lo->lo_queue, q->hardsect_size);
 		blk_queue_max_sectors(lo->lo_queue, q->max_sectors);
 		blk_queue_max_phys_segments(lo->lo_queue,q->max_phys_segments);
 		blk_queue_max_hw_segments(lo->lo_queue, q->max_hw_segments);
@@ -757,6 +756,8 @@
 		blk_queue_merge_bvec(lo->lo_queue, q->merge_bvec_fn);
 	}
 
+	set_blocksize(bdev, lo_blocksize);
+
 	kernel_thread(loop_thread, lo, CLONE_KERNEL);
 	down(&lo->lo_sem);
 
HTH,

-- 
Ben Slusky                      | The doctors x-rayed my head
sluskyb@paranoiacs.org          | and found nothing.
sluskyb@stwing.org              |               -Dizzy Dean
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