Designing a new init: low level communication

[Erich Schubert]

Hi,
> You can use /dev, which means it's accessable from very early in the
> boot, initng does this and it works well.  Also, are we sure this needs
> a writable filesystem?  I think if the socket exists it might not, I
> can't really remember ;)

That only works with FIFOs IIRC - sockets will disappear when closed,
so they only live for the runtime of the program. I don't know if
they'll actually get a node on the disk.
Where I'm skeptical with /dev is with static/udev/devfs.
You would need to ensure that the fifos "survive" the udev mounting.
For FIFOs I'd suggest the location /lib/debinit/fifoo
Since /lib also needs to be accessible early on, and the fifo is
somewhat static.

> I have a bit of experience here, as initng has been trying out a few
> here, fifo's were horrible and unix sockets worked very well, and we can
> solve issues here either with initramfs on boot or by waiting until /dev
> is mounted (which by initng is after the first script is launched).

Hmm... kind of a hack to require the first script to make /dev
writeable... but that sure would be a way we could take. Then we could
use socket semantics.
I've worked with fifos - on minit - and they were okay, the biggest
issue is that they occasionally are locked (so you need to retry) and
that you can't use them for having a monitor (e.g. the dbus
connector). We sure could use sockets for the dbus connector later on.
Can anyone comment on the following: "Connecting  to  the
       socket  object  requires  read/write permission.  This behavior differs
       from many BSD-derived systems which ignore permissions for  Unix  sock-
       ets. Portable programs should not rely on this feature for security."
And wheter we can work around that by placing the sockets into a
restricted directory?

> How much do we want to support remotly though?  Do we want a plugin api
> or a comunication api?  I imagine a comunication api would end up being
> considerably more advanced and a lot harder to implement, but that could
> be because I'm used to working with plugins ;)

I'm not sure about that. If we keep the messages to a minimum, it's
just about writing some structs to a fd. Not really difficult.

I'd like to have a statically linked init, since on a platform I'm
working on there is no dynamic linking available.

Also I think we are going to need this anyway, because I do not want
the dbus connector to be in init itself.

best regards,
Erich Schubert
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