Re: [PATCH] taskstats: Use better ifdef for alignment

Andrew Morton
2010-12-30T05:33:44Z

On Thu, 30 Dec 2010 00:26:34 -0500 Jeff Mahoney <jeffm@suse.com> wrote:

> On 12/29/2010 07:14 PM, Andrew Morton wrote:
> > On Wed, 29 Dec 2010 19:12:08 -0500 Jeff Mahoney <jeffm@suse.com> wrote:
> >
> >> Commit 4be2c95d added a null field to align the taskstats structure but
> >> the discussion centered around ia64. The issue exists on other platforms
> >> with inefficient unaligned access and adding them piecemeal would be
> >> an unmaintainable mess.
> >>
> >> This patch uses Dave Miller's suggestion of using a combination of
> >> CONFIG_64BIT && !CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS to determine
> >> whether alignment is needed.
> >>
> >> Note that this will cause breakage on those platforms with applications
> >> like iotop which had hard-coded offsets into the packet to access the
> >> taskstats structure.
> >
> > That seems a very good reason to not apply the patch.
> >
> > Tell us more, please...
>
> I don't want to rehash the same discussion

Please do so. That discussion went on for a long time over many emails
and multiple iterations of the patch. I personally have forgotten the
reasoning and if I could remember it, I wouldn't remember which version
of the patch it applied to.

Applying a patch which is *known* to break *known* userspace
applications is a quite extraordinary thing to do. We owe it to people
to fully explain the reasoning.