Peter Stuge peter at
Fri Sep 10 04:17:05 AEST 2021

Steffen Nurpmeso wrote:
> Well ok, thinking about this for more than just five minutes
> (sorry) i think care should be taken to cause graceful loop wakeup
> in any case.

I think the lack of feedback about removal success/failure inherent
with signals is problematic.

> Since _i think_ the poll(2) will not immediately tick due to
> SA_RESTART if the "timeout" parameter is not -1,

signal(7) on Linux says: "Which of these two behaviors occurs depends
on the interface and whether or not the signal handler was established
using the SA_RESTART flag (see sigaction(2)). The details vary across
UNIX systems; below, the details for Linux."

"The details vary across UNIX systems" suggests that you may need to
do research on this.

My signal(7) later says: "The following interfaces are never restarted after
being interrupted by a signal handler, regardless of the use of SA_RESTART;
they always fail with the error EINTR when interrupted by a signal handler:
* File descriptor multiplexing interfaces: ... poll(2) ..." - for Linux.

> add a few lines of code which create a socket(2), and perform
> a non-blocking connect(2) to the agent socket, followed by an
> immediate close(2).

There's no error handling after socket(), which is a problem in itself
but also ties into the feedback problem. Since this is intended to be
a security feature there really needs to be some feedback, making
direct interaction with the agents look a lot better, with the
significant additional advantage of needing zero new agent code.


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