Re: Hello world and couple of questions

From: Laurent Bercot <>
Date: Mon, 7 Sep 2015 17:13:43 +0200

  Hi Martin !

> After some smashing things together, I took original init.c from base FreeBSD
> src tree and removed parts until it's just rudimentary initialization
> function that execves into execlineb boot script.

  I'm interested in learning what you did: what is needed for FreeBSD to run a
script as init ? Why can't the kernel boot on stage 1 directly ?

> One problem I am having though, is "uncaught" logger dance, as unlike on linux,
> stage 1 dies with "broken pipe" signal when it tries to write to logger fifo
> (as it has no reader yet).

  Ah, yes. You just can't write to the pipe until the catch-all logger has
started, else it crashes like this.

> For now I got around that by redirecting stderr to logger only right before
> supervisor boots up, however that means initial messages appear only on
> console.
> Is there some way to buffer those from fifo until last resort logger
> starts (using tools in s6 packages)?
> Or can I somehow spawn logger before supervisor spins up and have it "descent"
> later into supervision tree?

  If you're certain that the amount of data you write will not exceed
PIPE_BUF, you may spawn a process that opens the fifo for reading, but
reads nothing, and only dies once the logger has started and opened the
fifo for reading again.
(Example: "background { redirfd -r 0 logger-fifo s6-pause }" and store
$! somewhere, then kill $! once the catch-all logger has opened
  I don't know at all if it would work: the behaviour of fifos when there
are several readers is unspecified by POSIX and totally implementation-
defined. It's definitely a hack. But it might do what you want.

  The best solution is still to have a very minimal stage 1 and not do
anything until the supervision tree is in place and the fifo has a
writer: anything that writes to stdout/stderr once you have redirected
them to the fifo, defer it to stage 2.
  There's an example of a minimal stage 1 in the examples/ subdirectory
of the s6 tarball. For another example, you can install the
s6-linux-init package: the s6-linux-init-maker tool will work on
FreeBSD. The generated scripts won't, but you can still look at them
to see how they perform a minimal stage 1 and delegate all the real
stuff to stage 2.

> Second problem is when I compile s6 and portable utils package with:
> ./configure --enable-static-libc
> all s6 tools are correctly identified by 'file' command as fully static ELFs,
> however s6-svstat for example fails to work correctly.
> It always reports given service as down.
> Without static libc it all works as intended.
> Is this a bug?

  It's certainly a bug, but it probably has more to do with the toolchain
and the way the programs are linked than with the s6 code. Can you please
send me a log of your build, as well as a strace (or ktrace, or whatever
FreeBSD tool can give a dump of the sequence of system calls) of the
failing s6-svstat invocation ?


Received on Mon Sep 07 2015 - 15:13:43 UTC

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