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From: Greg Depoire--Ferrer <greg@gregdf.com>
To: ell@lists.linux.dev
Subject: Fix bug when stdin is closed
Date: Sun,  8 May 2022 01:54:31 +0200
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Running iwd with FD 0 (stdin) closed fails because ell considers epoll_fd of 0 to mean failure. The first commit fixes
that bug.

However, it still won't work because ell/dhcp6-transport.c has a bug where it closes a uninitialized FD (FD 0 on my
machine) and that would cause an infinite loop because the epoll_wait call was returning EBADF. The second commit fixes
that bug.

I noticed that ell/dhcp-transport.c is prone to the same mistake as the udp_fd field is not initialized on construction,
but I don't know if the close can actually be called before the udp_fd field is set. Just to be sure, the third commit
initializes it.