openat2.2: Minor tweaks to the text

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/openat2.2

@@ -116,7 +116,9 @@ Any future extensions to
 will be implemented as new fields appended to the above structure,
 with a zero value in a new field resulting in the kernel behaving
 as though that extension field was not present.
-Therefore, users must ensure that they zero-fill this structure on
+Therefore, the caller
+.I must
+zero-fill this structure on
 initialization.
 (See the "Extensibility" section of the
 .B NOTES
@@ -204,6 +206,16 @@ end-users.
 Setting this flag indiscriminately for all uses of
 .BR openat2 ()
 may result in spurious errors on previously-functional systems.
+.\" FIXME I find the "previously-functional systems" in the previous
+.\" sentence a little odd (since openat2() ia new sysycall), so I would
+.\" like to clarify a little...
+.\" Are you referring to the scenario where someone might take an
+.\" existing application that uses openat() and replaces the uses
+.\" of openat() with openat2()? In which case, is it correct to
+.\" understand that you mean that one should not just indiscriminately
+.\" add the RESOLVE_NO_XDEV flag to all of the openat2() calls?
+.\" If I'm not on the right track, could you point me in the right
+.\" direction please.
 .TP
 .B RESOLVE_NO_SYMLINKS
 Disallow resolution of symbolic links during path resolution.