On Wed, Jan 31, 2018 at 04:46:20AM +0000, Al Viro wrote:

MSG and REMOVE are never triggered, so it's all down to {WR{NORM,BAND},RDHUP}.

Actually, POLLREMOVE is an amusing story (FSVO amusing): it's a part of
UnixWare /dev/poll ABI.  It had _not_ lasted in Linux - epoll_ctl()
EPOLL_CTL_DEL is used for the same purpose.  Chronology:

Oct 29 2002: davidel introduces it into the tree (and defines for i386)
Oct 31 2002: jgarzik has noticed broken alpha build and added definition
within a few hours the same had been done for itanic (davidm)
afternoon of the same day: Alan's merge of v850 adds definition there
Nov 1 2002: rmk adds definition for arm
Nov 2 2002: anton does the same for ppc64
Nov 2 2002: ak does the same for amd64
Nov 2 2002: davidel removes the sole user of that thing.
But that, of course, does not stop the propagation of the (now and forever)
useless definition - the same day it infects m68k; next day it's
parisc and sparc.  On Nov 8 it hits ppc32, Nov 17 - s390.
In June 2003 mips gets it, in July sh is brought in with that
thing already in it and the damn thing spreads to cris.  And so it goes;
the last flash of infection had been in 2007 when asm-generic/poll.h
had been introduced.

Its only user has lasted in the tree for four days.  Definitions
will probably stay forever...