kern/56277: ktruss -o /dev/stderr doesn't work

[dholland%NetBSD.org@localhost]

>Number:         56277
>Category:       kern
>Synopsis:       ktruss -o /dev/stderr doesn't work
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Jun 25 22:50:00 +0000 2021
>Originator:     David A. Holland
>Release:        NetBSD 9.9.85 (20210623)
>Organization:
>Environment:
System: NetBSD valkyrie 9.99.85 NetBSD 9.99.85 (VALKYRIE) #7: Wed Jun 23 18:32:25 EDT 2021  dholland@valkyrie:/usr/src/sys/arch/amd64/compile/VALKYRIE amd64
Architecture: x86_64
Machine: amd64
>Description:

% ktruss -o /dev/stderr ls
ktruss: file /dev/stderr, pid 29871: Unknown error: -5

ktracing ktruss shows:

  26761  26761 ktruss   CALL  ktrace(0x7f7fff219f92,0x2000000,0x1be,0x6889)
  26761  26761 ktruss   RET   ktrace -1 errno -5 Unknown error: -5

-5 is EDUPFD, clearly part of the workings of /dev/stderr, but this
should not escape to userland.

>How-To-Repeat:
	as above
>Fix:
	torches and pitchforks