implement poll and read
No matter if we implement some other kind of dirty notification mechanism,
it feels right to have pwqr pollable for overcommit.
Documentation:
- drop the "in kernel unpark" method, it sucks
- migrate to using non blocking "read" for the probing method.
- document the pollability and how read works in the pwqr_create "manpage".
lib:
- implement epoll_create with flags. It requires a kernel supporting
O_NONBLOCK/O_CLOEXEC flags to open(), I've been too lazy to implement
the emulation yet.
Signed-off-by: Pierre Habouzit <pierre.habouzit@intersec.com>