From: John McKell <mckellj@iomega.com>

This 2.6.1 patch works by setting gendisk->policy to the correct value
during initialization as the various drivers decide whether or not the disk
is writeable.  This patch persuades "blockdev --getro ..." to correctly
report the read-only state of a newly inserted disk.  This patch applies to
sr.c, sd.c and ide-floppy.c.  ide-cd.c already has this functionality built
into it.

Using an Iomega Zip drive as the test case...

Without the patch, I always see:

$ sudo blockdev --getro /dev/sda
0
$

That's only correct for writeable disks though.  Only when the patch
is applied do I see a write-protected disk described correctly:

$ sudo blockdev --getro /dev/sda
1
$