ssh-agent: remove all keys upon SIGUSR1..

[sdaoden]

With the advent of per-user temporary directories it became
hard for an administrator to remove all keys from all running
ssh-agent instances; what formerly could be done like so

if command -v ssh-add >/dev/null 2>&1; then
for a in /tmp/ssh-/agent.; do
[ -e "$a" ] || continue
act "SSH_AUTH_SOCK="$a" ssh-add -D </dev/null >/dev/null 2>&1 &"
inc
done
fi

has become a major undertaking, especially with even more
containerization. Being able to remove all keys from all agents
with a single command seems so desirable that it is available in
other agents in the software world.

[sdaoden]

Ah. Merde! Sorry, i thought "mergeable" meant the pull request!

[sdaoden]

..and one more sorry, this was not meant to be closed. I might become a github expert.

[djmdjm]

This looks good to me and the better signal handling could allow us to make cleanup_handler() a regular call in future (i.e. no longer calling it in signal context).

Would appreciate @daztucker taking a look at this too

[sdaoden]

(It is all taken from sshd.c of course. Only to mention it. I .. do not implement this cleanup like it is done in sshd.c in this context here now!?!)
Thank you for looking into this.

[sdaoden]

But surely not because of this changeset, no?
Never used CI as it is here; but there is no log at all for the failure, not even a build one?

[sdaoden]

(i do not understand this CI-fuzz github thing which fails in one out of dozens of things. this should have nothing to do with the little patch, i would think.)

[sdaoden]

Interestingly "the ppoll part has just recently been committed" almost as stated here.
Please let me allow one sentence: what a crappy attitude to leave that truly desired piece of code laying around for two years. git allows selective staging via "git add -p", and you would have had it 22 months ago.
Anyhow, this little pull request is now solely the SIGUSR1 handling, and all tests ran.

[sdaoden]

P.S.: "you would have had it 22 months ago": within less than 30 seconds.