userfaultfd: provide pid in userfault msg - add feat union

No ABI change, but this will make it more explicit to software that ptid
is only available if requested by passing UFFD_FEATURE_THREAD_ID to
UFFDIO_API.  The fact it's a union will also self document it shouldn't
be taken for granted there's a tpid there.

Link: http://lkml.kernel.org/r/20170802165145.22628-7-aarcange@redhat.com
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Alexey Perevalov <a.perevalov@samsung.com>
Cc: Maxime Coquelin <maxime.coquelin@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.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 665bf7a..5419e7d 100644 (file)
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -204,7 +204,7 @@ static inline struct uffd_msg userfault_msg(unsigned long address,
                 */
                msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WP;
        if (features & UFFD_FEATURE_THREAD_ID)
-               msg.arg.pagefault.ptid = task_pid_vnr(current);
+               msg.arg.pagefault.feat.ptid = task_pid_vnr(current);
        return msg;
 }
 

diff --git a/include/uapi/linux/userfaultfd.h b/include/uapi/linux/userfaultfd.h
index 2b24c28..d6d1f65 100644 (file)
--- a/include/uapi/linux/userfaultfd.h
+++ b/include/uapi/linux/userfaultfd.h
@@ -80,7 +80,9 @@ struct uffd_msg {
                struct {
                        __u64   flags;
                        __u64   address;
-                       __u32   ptid;
+                       union {
+                               __u32 ptid;
+                       } feat;
                } pagefault;
 
                struct {