[RFC PATCH v2 00/41] UUID and GUID user and group ids (*_r system calls)

[Theodore Tso]

On Thu, Oct 22, 2026 at 10:00:16AM -0500, Casey Schaufler wrote:
> 
> I can't see this being acceptable for a variety of reasons, including
> but not limited to performance and configuration complexity. It's a
> general solution for a special case or two, and the impact is significant.

Yeah. I agree it's a non-starter.  For one thing, it requires
replacing every single system call which uses a 32-bit uid or gid ---
either as an input parameter, a return value, or in a structure, such
as, "struct stat".  It also requires making breaking changes into
on-disk file formats that use a uid --- for example, /etc/passwd,
/etc/group, utmp/wtmp, etc.  If it will also break compatibility with
remote file systems that don't use a Windows SID --- e.g., nfsv3, AFS,
etc.  And that's before we even get to breaking things like tar files, etc.

I'll also note that customers that are most likely to need to use the
abominationm of Windows SIDs are also those that are likely to be
using proprietary third party binaries --- you know, silly things like
SAP R/3, Oracle Enterprise Database, db2, etc.  And if you use Windows
SIDs as user id's in your /etc/passwd, then binaries that are still
using the traditional system calls will get the overflow 32-bit number
--- and break.

I suspect it will be much more useful to simply add a supplementary
user id and group id which is only used by those file systems that
*care* about Windows SID's, and assume that everything else will use
true, traditional Unix uids and gids.  I also suspect that we should
be stashing the supplementary id's as extended attributes for the file
systems.  That way we can much more quickly and easily add support to
ext4, xfs, btrfs, etc., as file systems that can be used as backing
stores for NFSv4 and CIFS for those (few) environments that care about
Windows SID's.

						- Ted

P.S., From my perspective, Windows SID's are actually the legacy
ID's. especially as more and more people flee Microslop's Windows 11
and moving to Linux and MacOS.  :-)