memfd: export alloc_file()

memfd: export alloc_file()

Patch series "mm: memfd_luo hotfixes".

This series contains a couple of fixes for memfd preservation using LUO.

This patch (of 3):

The Live Update Orchestrator's (LUO) memfd preservation works by
preserving all the folios of a memfd, re-creating an empty memfd on the
next boot, and then inserting back the preserved folios.

Currently it creates the file by directly calling shmem_file_setup().
This leaves out other work done by alloc_file() like setting up the file
mode, flags, or calling the security hooks.

Export alloc_file() to let memfd_luo use it.  Rename it to
memfd_alloc_file() since it is no longer private and thus needs a
subsystem prefix.

Link: https://lkml.kernel.org/r/20260122151842.4069702-1-pratyush@kernel.org
Link: https://lkml.kernel.org/r/20260122151842.4069702-2-pratyush@kernel.org
Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>