[systemd-devel] systemctl escaping of unit names

[Zbigniew Jędrzejewski-Szmek]

On Sun, Jul 06, 2014 at 04:01:52PM +0200, Gero Treuner wrote:
> Hello everybody,
> 
> I join this mailing list because I want to discuss extending systemctl
> with a method to escape unit names. Currently systemd and systemctl
> deal with escaped unit names but there are many potential name sources
> which doesn't have out-of-the-box escaping methods.
> 
> The issue is a Debian bug related to a service unit for a network
> device [0].
> 
> 
> Current situation
> 
> * systemctl somewhat supports escaping of paths for the unit types
>   device and mount (in function unit_name_mangle).
> 
> * systemctl prevents broken unit names by escaping invalid characters,
>   but doesn't escape in a transparent way clear_name->escaped_name
>   (it isn't supposed to do that, because "ready-to-use" i. e. escaped
>   unit names are expected)
> 
> * systemd does not provide access to the escaping methods in a
>   practical way for most environments. Although the escape mechanism is
>   documented, have systemd integrators implement it by themself has some
>   disadvantages:
>   1. It can't be simply done in shell only.
>   2. Lots of independently created escapes potentially lead to errors,
>      which can cause various effects up to security risks or system
>      hangs.
> 
> 
> Proposal
> 
> 1. Extend systemctl unit name interpretation with a syntax to escape in
>    controlled manner, preferably capable of escaping only parts of a
>    given name to support compound names with verbatim content (given by
>    users typing anything they imagine in their GUI).
Hi,
this is not useful. The *instance* part is escaped, because it refers
to file system paths and other things which are not controlled by systemd
or by users of systemd. Unit *names* are controlled, so it's much more
productive to simply set some rules which limit what is allowed. All
units have a free-text Description= field, which can hold whatever the
user wants.

> I and possible more in the world are really tired of implementing
> nested escapes.
This is a good reason to implement a helper in systemctl...

> Therefore the approach is to give the number of
> characters instead of any end token. This is friendly to programmers
> and CPUs, isn't it?
... no, a few extra cycles spent on string processing do not really
matter.

> [0] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=747044

Zbyszek