[dm-devel] [PATCH v2] dm: Fix alignment stacking on partitioned devices
Mike Snitzer
snitzer at redhat.com
Fri Jan 8 20:28:07 UTC 2010
On Fri, Jan 08 2010 at 1:41pm -0500,
Martin K. Petersen <martin.petersen at oracle.com> wrote:
> >>>>> "Mike" == Mike Snitzer <snitzer at redhat.com> writes:
>
> Mike,
>
> Mike> Seems I took the time to add a comment whose FIXME doesn't ring
> Mike> many bells now! But ignoring that, the comment before the FIXME
> Mike> is making a veiled reference to userspace having consumed
> Mike> alignment_offset.
>
> I read and understood the comment. But even then explicitly zeroing out
> those two values didn't make sense (because if user space did in fact do
> the right thing they'd always be zero).
>
> I know that the DM utilities take care of business. And that DM devices
> are special because they are always set up by user space and not a
> kernel discovery process.
>
> But since the code *is* in place to validate things I'm not so keen on
> you clearing fields that have been calculated and have a meaning. For
> me it masked a case where the DM utilities did the wrong thing (because
> they were old).
>
> With the Enterprise Linux hat on it is easy for us to specify that you
> must use this version of the kernel and the device mapper utilities.
> But reality is that lots of people are running upstream kernels on
> distributions with older userland. And some distributions get things
> wrong, ship broken bits, etc.
>
> It's great that new DM utils will transparently adjust the starting
> offset. That's the way it's supposed to work. No arguments there.
>
> My main concern is making sure that we never get into a case where we
> run with misaligned components without indicating that there is a
> problem. Ever! Regardless of which DM utils might be in place.
>
> We have the power to get that right. All the pieces are in place. I'd
> simply like us to stop making assumptions about user space always doing
> the right thing.
Yeap, I already agreed that those 2 lines should be removed (in the
p.s. of my previous mail). They really aren't serving any purpose and
their justification was/is tenuous at best.
I'll get the fix, for 2.6.33, to Alasdair shortly.
Mike
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