• David Herrmann's avatar
    mm: allow drivers to prevent new writable mappings · 4bb5f5d9
    David Herrmann authored
    This patch (of 6):
    The i_mmap_writable field counts existing writable mappings of an
    address_space.  To allow drivers to prevent new writable mappings, make
    this counter signed and prevent new writable mappings if it is negative.
    This is modelled after i_writecount and DENYWRITE.
    This will be required by the shmem-sealing infrastructure to prevent any
    new writable mappings after the WRITE seal has been set.  In case there
    exists a writable mapping, this operation will fail with EBUSY.
    Note that we rely on the fact that iff you already own a writable mapping,
    you can increase the counter without using the helpers.  This is the same
    that we do for i_writecount.
    Signed-off-by: default avatarDavid Herrmann <dh.herrmann@gmail.com>
    Acked-by: default avatarHugh Dickins <hughd@google.com>
    Cc: Michael Kerrisk <mtk.manpages@gmail.com>
    Cc: Ryan Lortie <desrt@desrt.ca>
    Cc: Lennart Poettering <lennart@poettering.net>
    Cc: Daniel Mack <zonque@gmail.com>
    Cc: Andy Lutomirski <luto@amacapital.net>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
inode.c 50 KB