userfaultfd: Rename uffd_api.bits into .features

This is (seems to be) the minimal thing that is required to unblock
standard uffd usage from the non-cooperative one.  Now more bits can be
added to the features field indicating e.g.  UFFD_FEATURE_FORK and others
needed for the latter use-case.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: Sanidhya Kashyap <sanidhya.gatech@gmail.com>
Cc: zhang.zhanghailiang@huawei.com
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Andres Lagar-Cavilla <andreslc@google.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Hugh Dickins <hughd@google.com>
Cc: Peter Feiner <pfeiner@google.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Huangpeng (Peter)" <peter.huangpeng@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 9bc256d..0756d97 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -884,7 +884,7 @@
 		goto out;
 	}
 	/* careful not to leak info, we only read the first 8 bytes */
-	uffdio_api.bits = UFFD_API_BITS;
+	uffdio_api.features = UFFD_API_FEATURES;
 	uffdio_api.ioctls = UFFD_API_IOCTLS;
 	ret = -EFAULT;
 	if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
@@ -941,7 +941,7 @@
 	 *	protocols: aa:... bb:...
 	 */
 	seq_printf(m, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n",
-		   pending, total, UFFD_API, UFFD_API_BITS,
+		   pending, total, UFFD_API, UFFD_API_FEATURES,
 		   UFFD_API_IOCTLS|UFFD_API_RANGE_IOCTLS);
 }
 #endif