userfaultfd: merge fs/userfaultfd.c into mm/userfaultfd.c

Patch series "userfaultfd: merge fs/userfaultfd.c into mm/userfaultfd.c",
v3.

These patches merge fs/userfaultfd.c into mm/userfaultfd.c and make
functions used only inside mm/userfaultfd.c static.


This patch (of 2):

Historically userfaultfd implementation has been split between
fs/userfaultfd.c and mm/userfaultfd.c.

The mm/ part implemented memory management operations, while the fs/ part
implemented file descriptor handling and called into the mm/ part for the
actual memory management work.

This separation is quite artificial and fs/userfaultfd.c does not seem to
belong to fs/ because it's only a user if vfs APIs and like for other
users, for example, memfd and secretmem, the file descriptor handling
could live in mm/ as well.

"Append" fs/userfaultfd.c to mm/userfaultfd and update fs/Makefile and
MAINTAINERS accordingly.

No intended functional changes.

Link: https://lore.kernel.org/20260523173759.3964908-1-rppt@kernel.org
Link: https://lore.kernel.org/20260523173759.3964908-2-rppt@kernel.org
Assisted-by: Copilot:claude-opus-4-6
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Christian Brauner (Amutable) <brauner@kernel.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

MAINTAINERS

@@ -17085,7 +17085,6 @@ R:	Peter Xu <peterx@redhat.com>
 L:	linux-mm@kvack.org
 S:	Maintained
 F:	Documentation/admin-guide/mm/userfaultfd.rst
-F:	fs/userfaultfd.c
 F:	include/asm-generic/pgtable_uffd.h
 F:	include/linux/userfaultfd_k.h
 F:	include/uapi/linux/userfaultfd.h

fs/Makefile

@@ -27,7 +27,6 @@ obj-y				+= anon_inodes.o
 obj-$(CONFIG_SIGNALFD)		+= signalfd.o
 obj-$(CONFIG_TIMERFD)		+= timerfd.o
 obj-$(CONFIG_EVENTFD)		+= eventfd.o
-obj-$(CONFIG_USERFAULTFD)	+= userfaultfd.o
 obj-$(CONFIG_AIO)               += aio.o
 obj-$(CONFIG_FS_DAX)		+= dax.o
 obj-$(CONFIG_FS_ENCRYPTION)	+= crypto/