Some suggestions on old-fashioned usage with s6 2.10.x

["Casper Ti. Vector" <caspervector@gmail.com>]

I did not actively follow the recent evolution of s6, and have just been
bitten badly by s6 2.10.x on my Alpine servers (where slew [1] is used
of course) when it comes along with other updates.

[1] <https://gitea.com/CasperVector/slew>

First, kernel panic on booting.  With some tentative echo(1) invocations
(with I/O redirections to /dev/console when necessary) and messing with
console resolution (so I could see the outputs before the panic), I
found the problem occurred with `s6-svscan' exiting because of the
legacy `-s' option in [2].  The fix itself is trivial, but it would be
better if we kept the option supported for a transition period, and that
only removed it from the manual pages while urging users to get rid of
it.  After all, in this case, silently ignoring `-s' is behaviourly
similar to (if not perfectly compatible with) old `s6-svscan'.

[2] <https://gitea.com/CasperVector/slew/src/commit/
             fe32c2f1e3bf5cf700ff99d13eb13720353823bb/init/rc.boot>

Second, `s6-svscan' now waits for its `s6-supervise' children to exit
before exec()ing `.s6-svscan/finish', so it hangs forever (save for
magic SysRq) due to the catch-all logger on halting.  I do know that the
recommended way to shut down is to use `s6-linux-init-shutdown', but
it will be nice if the old-fashioned way (with stage 1 and stage 3 as
static scripts) is supported as well after minimal modifications to both
s6 and (for instance) slew.  I also understand that `s6-svc -X' has been
removed, and that the invocation in [3] would no longer work anyway
because [3] is exec()ed by `s6-svscan'.  However, I think the following
way is practical yet minimal: introduce an option (perhaps still `-X')
of `s6-svc', but that tells `s6-supervise' to exit normally *upon
receiving SIGTERM or SIGHUP* (this is where the behaviour differs from
the old `s6-svc -X') without waiting for the children to exit; then move
the `s6-svc -X' invocation from `rc.halt' into `rc.fin' (where `s6-rc -d
change all' is also spawn).

[3] <https://gitea.com/CasperVector/slew/src/commit/
             fe32c2f1e3bf5cf700ff99d13eb13720353823bb/init/rc.halt>

Any suggestions?

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