[PATCH 6/6] userfaultfd: provide pid in userfault msg - add feat union

[Andrea Arcangeli <aarcange@redhat.com>]

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.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
---
 fs/userfaultfd.c                 | 2 +-
 include/uapi/linux/userfaultfd.h | 4 +++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index ae044650dffa..9677d862ed53 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -207,7 +207,7 @@ 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 2b24c28d99a7..d6d1f65cb3c3 100644
--- 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 {

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