mm: implement file_is_dev_zero() to uniquely identify /dev/zero

To lay the foundation for a future change that converts
MAP_PRIVATE-/dev/zero mappings to be truly anonymous, add the ability to
uniquely identify these mappings.

With the memory character device now part of mm/ this is trivially
achievable through a file_is_dev_zero() predicate that simply tests that
the file operation hooks are zero_fops.

Also update userland VMA tests to expose file_is_dev_zero() and provide
a stub zero_fops for testing.

Link: https://lore.kernel.org/20260926-map-private-dev-zero-v3-2-d4781e84ccfc@kernel.org
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Jan Kara <jack@suse.cz>

0 files changed, 0 insertions, 0 deletions