Re: [PATCH 5/6] userfaultfd: decouple fault reason from VMA flags

[Mike Rapoport <rppt@kernel.org>]

On Mon, Aug 24, 2026 at 04:46:14PM +0200, David Hildenbrand (Arm) wrote:
> On 8/23/26 14:17, Mike Rapoport (Microsoft) wrote:
> > Introduce enum uffd_reason to define reasons for user faults rather than
> > overload VM_UFFD_* VMA flags for that.
> > 
> > Using a dedicated enum makes the code clearer and decoupling the fault
> > reason from VMA flags clears the way for moving the uffd mode bits out
> > of VMA namespace.
> > 
> > No functional change.
> > 
> > Assisted-by: copilot:claude-opus-4.6
> > Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> > ---
> >  include/linux/userfaultfd_k.h    | 16 ++++++++++++++--
> >  include/uapi/linux/userfaultfd.h |  6 +++---
> >  mm/huge_memory.c                 |  6 +++---
> >  mm/hugetlb.c                     | 10 +++++-----
> >  mm/memory.c                      | 10 +++++-----
> >  mm/shmem.c                       |  4 ++--
> >  mm/userfaultfd.c                 | 30 +++++++++++++++---------------
> >  7 files changed, 47 insertions(+), 35 deletions(-)
> > 
> > diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h
> > index 45355bdb4ec7..f401623f315d 100644
> > --- a/include/linux/userfaultfd_k.h
> > +++ b/include/linux/userfaultfd_k.h
> > @@ -9,6 +9,18 @@
> >  #ifndef _LINUX_USERFAULTFD_K_H
> >  #define _LINUX_USERFAULTFD_K_H
> >  
> > +#include <linux/bits.h>
> > +
> > +/* Fault reason #PF handler passes to handle_userfault() */
> > +enum uf_reason {
> 
> Can we just call this "userfault_reason" or "uffd_reason" ? Maybe the latter is
> actually what we want?

userfault_reason sounds better to me.

It describes what kind of user fault we are handling and the 'fd' part has
nothing to do with it. 
We do use uffd as a short name for the subsystem, but still most if not all
userfaultfd "external" APIs use userfault_ prefix.

uf_ was an attempt to make it wee shorter :)
 
> -- 
> Cheers,
> David

-- 
Sincerely yours,
Mike.