Re: [PATCH, RFC] libxfs: check the size of on-disk data structures

Darrick J. Wong
2023-12-01T02:06:59Z

On Fri, Nov 10, 2023 at 06:08:46AM +0100, Christoph Hellwig wrote:
> On Thu, Nov 09, 2023 at 11:52:33AM -0800, Darrick J. Wong wrote:
> > > +#ifndef BUILD_BUG_ON_MSG
> > > +#define BUILD_BUG_ON_MSG(a, b) BUILD_BUG_ON(a)
> >
> > How difficult would it be to port the complex kernel macros that
> > actually result in the message being emitted in the gcc error output?
> >
> > It's helpful that when the kernel build breaks, the robots will report
> > exactly which field/struct/whatever tripped, which makes it easier to
> > start figuring out where things went wrong on some weird architecture.
>
> I did try to pull the entire compile time assert machinery from
> the kernels compiler_types.h in, especially as atomic.h already uses
> a differnet part of it. After it pulled in two more depdendencies
> I gave up, but in principle it should be entirely doable.
>
> > Otherwise I'm all for porting xfs_ondisk.h to xfsprogs. IIRC I tried
> > that a long time ago and Dave or someone said xfs/122 was the answer.
>
> I'd much prefer to do it in C code and inside the libxfs we build.
> If we can agree on that and on killing off xfs/122 I'll look into
> porting the more complex compile time assert.
>
> The other option would be to switch to using static_assert from C11,
> which doesn't allow a custom message, but at least the default message
> isn't confusing as hell.

I copy-pasta'd the whole mess from compiler_types.h and build_bug.h into
include/xfs.h. It works, but it might be kinda egregious though.

--D