[systemd-devel] How to start a service when a device is created under /dev/pts/

[Mantas Mikulėnas]

On Mon, Feb 13, 2023 at 3:21 PM Giuseppe Sacco <giuseppe at sguazz.it> wrote:

> Il giorno lun, 13/02/2023 alle 12.12 +0200, Mantas Mikulėnas ha
> scritto:[...]
> > I'm not entirely sure whether it even makes sense for a .service unit
> > to wait for a specific pty? I mean, the entire design of ptys is that
> > they're assigned on a first-come basis and there's no way for a process
> > to claim a specific pty for itself, so there's no way for
> > faxgetty at .service to be sure that pty/0 is your fax thing and not e.g.
> > someone's xterm or an incoming SSH connection.
> >
> > What is supposed to be creating /dev/pts/0 in your case? It might be
> > simplest to have the same software directly start
> > faxgetty@<ptyname>.service as well.
>
> In this scenario, the ptys are created by software like iaxmodem (that uses
> asterisk) when its daemon starts. Some more information is available at
> Debian bug 1031200 (http://bugs.debian.org/1031200) and a suggested
> solution is to change the unit and depend on the pty daemon service and on
> the a file system link in /dev that points to the real device in /dev/pty/
> (the link being created by the pty service at startup time).
>
> Something like:
>
> [Unit]
> Description=HylaFAX faxgetty %I
> Wants=iaxmodem.service dev-%i.device
>

I can't see how that would work. Udev doesn't issue events for symlinks – a
symlink to something that's not a "device" is still not a device.

Would it be enough to order faxgetty After=iaxmodem.service, i.e. wait
until it has created *all* of the ptys that it was set up to create? Are
they preconfigured or do they show up dynamically?

-- 
Mantas Mikulėnas
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.freedesktop.org/archives/systemd-devel/attachments/20230213/89b0c682/attachment.htm>