tree 901d23e7259d473dd70d5082e9ffedd4cc881e27
parent 6760845da6587785f49af564cfad336fb9fe1586
author Harald Welte <laforge@osmocom.org> 1603049053 +0200
committer laforge <laforge@osmocom.org> 1603465745 +0000

select: Migrate over to poll()

select is an ancient interface with weird restrictions, such as
the fact that it cannot be used for file descriptor values > 1024.

This may have been sufficient 40 years ago, but certainly is not in
2020.  I wanted to migrate to epoll(), but unfortunately it doesn't
work well with the fact that existing programs simply set osmo_fd.flags
without making any API calls at the time they change those flags.

So let's do the migration to poll() as a first step, and then consider
epoll() as a second step further down the road, after introducing new
APIs and porting applications over.

The poll() code introduced in this patch is not extremely efficient,
as it needs to do extensive linked list iterations after poll() returns
in order to find the osmo_fd from the fd.  Optimization is possible,
but let's postpone that to a follow-up patch.

At compile time, a new --enable-force-io-select argument can be given
to configure, forcing the use of the old select() backend instead of the
new poll() based backend.

Change-Id: I9e80da68a144b36926066610d0d3df06abe09bca