Re: [PATCH 1/2] mm: fix mmap errno value when MAP_DROPPABLE is not supported

David Hildenbrand (Arm)
2026-04-02T07:17:33Z

On 4/2/26 02:44, Andrew Morton wrote:
> On Wed, 1 Apr 2026 17:34:16 -0700 Anthony Yznaga <anthony.yznaga@oracle.com> wrote:
>
>> On configs where MAP_DROPPABLE is not supported (currently any 32-bit
>> config except for PPC32), mmap fails with errno set to ENOTSUPP.
>> However, ENOTSUPP is not a standard error value that userspace knows
>> about. The acceptable userspace-visible errno to use is EOPNOTSUPP.
>> checkpatch.pl has a warning to this affect.
>
> Sounds very reasonable.
>
> EOPNOTSUPP is clearly a networking thing so what on earth is it doing
> coming out of mmap code? Our poor operator is now looking at a networking
> error code and wondering what this supposedly non-networking
> application is up to.
>
> But just that's a pet peeve - I lost that one decades ago.
>
>> Fixes: 9651fcedf7b9 ("mm: add MAP_DROPPABLE for designating always lazily freeable mappings")
>
> Nearly two years ago so I think I'll add this to mm-unstable for
> 7.1-rc1 and shall let it trickle back a little more slowly than might a
> 7.0-rcX hotfix.
>
>

Acked-by: David Hildenbrand (Arm) <david@kernel.org>

But

~/git/linux/mm$ git grep ENOTSUPP
hugetlb_vmemmap.c: ret = -ENOTSUPP;
mmap.c: return -ENOTSUPP;

Should we fix up the other one as well?

--
Cheers,

David