select() and poll() inconsistency in writability test

[Frank van Maarseveen <frankvm@frankvm.com>]

A pipe without readers will yield EPIPE/SIGPIPE when trying to write()
into. A broken or shutdown TCP connection will behave the same modulo
networking errors (which are returned only once as it seems).

A pipe without readers will set POLLERR in pipe_poll() and this turns
up as being writable according to select() so it won't wait. However, a
TCP connection no longer open [for writing] does not set POLLERR/POLLOUT
in tcp_poll(): so it is not yet writable according to select() causing it
to wait. This is not consistent behavior.

Shouldn't the kernel set POLLOUT in both "EPIPE" cases instead of
POLLERR/nothing as it does now?

-- 
Frank
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