Re: [Bug 219203] New: xfsprogs-6.10.0: missing cast in /usr/include/xfs/xfs_fs.h(xfs_getparents_next_rec) causes error in C++ compilations

[Dave Chinner <david@fromorbit.com>]

On Tue, Aug 27, 2024 at 09:07:03PM +0000, bugzilla-daemon@kernel.org wrote:
> https://bugzilla.kernel.org/show_bug.cgi?id=219203
> 
>             Bug ID: 219203
>            Summary: xfsprogs-6.10.0: missing cast in
>                     /usr/include/xfs/xfs_fs.h(xfs_getparents_next_rec)
>                     causes error in C++ compilations
>            Product: File System
>            Version: 2.5
>           Hardware: All
>                 OS: Linux
>             Status: NEW
>           Severity: normal
>           Priority: P3
>          Component: XFS
>           Assignee: filesystem_xfs@kernel-bugs.kernel.org
>           Reporter: kernel@mattwhitlock.name
>         Regression: No
> 
> C allows implicit casts from void* to any pointer type, but C++ does not. Thus,
> when including <xfs/xfs_fs.h> in a C++ compilation unit, the compiler raises
> this error:
> 
> /usr/include/xfs/xfs_fs.h: In function 'xfs_getparents_rec*
> xfs_getparents_next_rec(xfs_getparents*, xfs_getparents_rec*)':
> /usr/include/xfs/xfs_fs.h:915:16: error: invalid conversion from 'void*' to
> 'xfs_getparents_rec*' [-fpermissive]
>   915 |         return next;
>       |                ^~~~
>       |                |
>       |                void*
> 
> 
> The return statement in xfs_getparents_next_rec() should have used an explicit
> cast, as the return statement in xfs_getparents_first_rec() does.
> 
> --- /usr/include/xfs/xfs_fs.h
> +++ /usr/include/xfs/xfs_fs.h
> @@ -912,7 +912,7 @@
>         if (next >= end)
>                 return NULL;
> 
> -       return next;
> +       return (struct xfs_getparents_rec *)next;
>  }

We shouldn't be putting static inline code in xfs_fs.h. That header
file is purely for kernel API definitions. Iterator helper functions
aren't part of the kernel API definition - they should be in some
other exported header file if they are needed at all. The helpers
could be defined in the getparents man page in the example code that
uses them rather than exposing the C code to the world...

I note that we've recently added a static inline function type
checking function to xfs_types.h rather than it being an external
function declaration, so there's more than one header file that
needs cleanup....

-Dave.
-- 
Dave Chinner
david@fromorbit.com