* Alexey Perevalov (a.pereva...@samsung.com) wrote: > On 05/24/2017 02:33 PM, Peter Xu wrote: > > On Wed, May 24, 2017 at 09:45:48AM +0300, Alexey wrote: > > > > [...] > > > > > > > return false; > > > > > } > > > > > - ioctl_mask = (__u64)1 << _UFFDIO_REGISTER | > > > > > - (__u64)1 << _UFFDIO_UNREGISTER; > > > > > + ioctl_mask = 1 << _UFFDIO_REGISTER | > > > > > + 1 << _UFFDIO_UNREGISTER; > > > > Could I ask why we explicitly removed (__u64) here? Since I see the > > > > old one better. > > > maybe my change not robust, in any case thank to point me, but now I > > > think, here should be a constant instead of ioctl_mask, like > > > UFFD_API_IOCTLS, the total meaning of that check it's make sure kernel > > > returns to us no error and accepted features. > > > ok, from the beginning: > > > > > > if we request unsupported feature (we check it before) or internal > > > state of userfault ctx inside kernel isn't UFFD_STATE_WAIT_API (for > > > example we are in the middle of the coping process) > > > ioctl should end with EINVAL error and ioctls field in > > > uffdio_api will be empty > > > > > > Right now I think ioctls check for UFFD_API is not necessary. > > > We just say here, we will use _UFFDIO_REGISTER, _UFFDIO_UNREGISTER, > > > but kernel supports it unconditionally, by contrast with > > > UFFDIO_REGISTER ioctl - it also returns ioctl field in uffdio_register > > > structure, here can be a variations. > > Sorry I didn't get the point... > I misprinted > >We just say here, we will use _UFFDIO_REGISTER > > > s/_UFFDIO_REGISTER/_UFFDIO_API/g > but the point, ioctl_mask is not necessary here, kernel always returns it. > But for _UFFDIO_UNREGISTER, later, not in this function, yes that check is > required.
But Peter's only point was that to build the mask it's better to keep the (__u64) cast for safety. Dave > > > > AFAIU here (__u64) makes the constant "1" a 64bit variable. Just like > > when we do bit shift we normally have "1ULL<<40". I liked it since > > even if _UFFDIO_REGISTER is defined as >32 it will not overflow since > > by default a constant "1" is a "int" typed (and it's 32bit width). > > > Thanks, > > > > -- > Best regards, > Alexey Perevalov -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK