Re: CVS commit: src/sbin/newfs

[Taylor R Campbell <campbell+netbsd-source-changes-d%mumble.net@localhost>]

> Date: Wed, 05 Jul 2023 07:03:09 -0400
> From: Greg Troxel <gdt%lexort.com@localhost>
> References: <20230705105858.33080FA89%cvs.NetBSD.org@localhost>
> 
> "Taylor R Campbell" <riastradh%netbsd.org@localhost> writes:
> 
> > Revert "newfs(8): Ensure A divides S before aligned_alloc(A, S)."
> >
> > C17 lifted this restriction.
> 
> I know we have only two toolchains maintained in tree, but did we really
> decide to require C17?

Well, what happened is:

1. I was drafting posix_memalign and aligned_alloc for libbsdmalloc in
   response to the thread about static program size yesterday, and
   carefully reading the specs -- POSIX 2018, C11 -- to make sure I
   got all the details right.

2. I saw a silly restriction in C11, that aligned_alloc(A, S) requires
   A to divide S.

3. For the sake of encouraging portable code, I figured we should
   enforce that restriction, so I went ahead and did that in both the
   libbsdmalloc front end I was writing and in jemalloc.  (This caused
   a bunch of tests to start failing.)

4. I audited all the uses of aligned_alloc in tree to make sury they
   meet the restriction (which fixed the tests).

5. Someone pointed out that the silly restriction that was imposed in
   C11 had actually been lifted in C17:

        (C11) The value of alignment shall be a valid alignment
        supported by the implementation and the value of size shall be
        an integral multiple of alignment.

        (C17) If the value of alignment is not a valid alignment
        supported by the implementation the function shall fail by
        returning a null pointer.

6. So I reverted the jemalloc enforcement of the C11 restriction, and
   reverted the fixes made to conform to it, and removed the
   restriction in the new libbsdmalloc code, and we're more or less
   back to where we started.

Except I am now reminded that I updated t_posix_memalign.c to verify
this silly restriction of aligned_alloc, so I'd better go fix that
before a bunch of tests start failing again!