Re: [HEADSUP] ucred / group changes in FreeBSD 15.0

On 8/8/25 03:36, Dag-Erling Smørgrav wrote:
> Kyle Evans <kevans@FreeBSD.org> writes:
>> The major struct ucred change[0] here is that we now track the egid
>> outside of the cr_groups array.  We've had a cr_gid macro to alias
>> cr_groups[0] for over 30 years, but the macro has now been replaced by
>> actual members in struct ucred and struct xucred.  In the xucred case,
>> we use some union trickery to alias it to the first element of
>> cr_groups to avoid breaking the ABI.
> 
> Why not just:
> 
> 	gid_t	cr_gid;		/* effective group id */
> 	gid_t	cr_groups[XU_NGROUPS - 1];
> 
> which would be fully ABI compatible?
> 

kib might have a more well-reasoned opinion here, but my perhaps 
slightly-paranoid view was that we should consider cr_groups sizing to 
be a property of the ABI since it's a cross-platform interface.  I 
didn't look into ports here to decide if anybody does silly things, 
since it's easy to preserve for 15.0.