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

[Andrew Morton]

On Wed,  1 Apr 2026 17:34:16 -0700 Anthony Yznaga <anthony.yznaga@xxxxxxxxxx> 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.