Question about D-Bus and cygrunsrv

[Mike Brady]

Hello again.

I've returned to this continuing problem and come up with a short piece of code which seems to exemplify this problem. It works in Linux and doesn't work in Cygwin.

Basically, the code is an attempt to get a "name" on the D-Bus "system bus" which could be used to provide a system-wide service using the D-Bus IPC protocol.

The attempt to get a name succeeds on Linux (Ubuntu 19.04) and fails on Cygwin (3.0.7). The code uses the high-level GDbus interface that is part of GIO (https://developer.gnome.org/gio/stable/ch01.html <https://developer.gnome.org/gio/stable/ch01.html>).

Another piece of sample code that uses the regular D-Bus library (libdbus1-devel in Cygwin) seems to work perfectly, which seems to me to suggest that whatever this probelm is, it is not a security issue.

Both of these samples are set up as automake projects and include config and policy files. I'd be happy to share or publish them wherever convenient...

Regards
Mike


> On 22 Feb 2019, at 09:55, Corinna Vinschen <corinna-cygwin@cygwin.com> wrote:
> 
> Hey Mike,
> 
> On Feb 21 16:56, Mike Brady wrote:
>> Hello again. Further to the rather vague email below, here is a link to what I did to install Shairport Sync on a fresh Cygwin installation: 
>> 
>> https://github.com/mikebrady/shairport-sync/blob/development/CYGWIN.md <https://github.com/mikebrady/shairport-sync/blob/development/CYGWIN.md> <https://github.com/mikebrady/shairport-sync/blob/development/CYGWIN.md <https://github.com/mikebrady/shairport-sync/blob/development/CYGWIN.md>>
>> 
>> Regards
>> Mike
>> 
>> 
>>> On 20 Feb 2019, at 21:50, Mike Brady <mikebrady@eircom.net> wrote:
>>> 
>>> Hi there. I'm trying to set up Shairport Sync as a CYGWIN service, and I'm trying to use cygrunsrv.
>>> 
>>> Briefly, I can get everything to work properly except the D-Bus interface -- when shairport-sync is installed as a service, it can't "own" a well-known name on the "system" D-Bus.
>>> 
>>> I built a configuration and installer for shairport sync essentially by copying the avahi-daemon-config file.
>>> 
>>> The Avahi deamon uses the system D-Bus successfully under the username "SYSTEM" and without (AFAICS) changing IDs. But for the life of me, I can't get Shairport Sync to work the same way.
>>> 
>>> Incidentally, if I change the D Bus policy file for Shairport Sync to be allowed to own its well-known name on D Bus when running under the logged in account, everything is peachy.
>>> 
>>> Any suggestions gratefully received. Incidentally, I'm the main developer of Shairport Sync -- https://github.com/mikebrady/shairport-sync.
>>> 
>>> Best wishes
>>> Mike Brady
>>> 
> 
> You have been heard, but I have not the faintest clue what d-bus or,
> FWIW, avahi are doing.  Ideally, if you could break down the problem
> to a simple, self-contained testcase which shows what exactly is not
> working on a plain libc level, help may be possible :}
> 
> 
> Corinna
> 
> -- 
> Corinna Vinschen
> Cygwin Maintainer


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