[pulseaudio-discuss] System mode & SHM

[Tanu Kaskinen]

On Sat, 2014-12-06 at 23:59 +0100, Pali Rohár wrote:
> On Saturday 06 December 2014 23:20:10 Tanu Kaskinen wrote:
> > On Sun, 2014-11-23 at 14:43 +0100, Pali Rohár wrote:
> > > On Sunday 23 November 2014 09:25:46 David Henningsson wrote:
> > > > On 2014-11-22 22:39, Pali Rohár wrote:
> > > > > Hello,
> > > > > 
> > > > > it is possible to enable shared memory when pulseaudio
> > > > > is stared in system mode?
> > > > 
> > > > Not without recompiling PulseAudio, the relevant code is
> > > > in src/pulsecore/protocol_native.c, function
> > > > command_auth:
> > > > 
> > > > #ifdef HAVE_CREDS
> > > > 
> > > >      if (do_shm) {
> > > >      
> > > >          /* Only enable SHM if both sides are owned by the
> > > > 
> > > > same * user. This is a security measure because otherwise
> > > > data * private to the user might leak. */
> > > > 
> > > >          const pa_creds *creds;
> > > >          if (!(creds = pa_pdispatch_creds(pd)) || getuid()
> > > >          !=
> > > > 
> > > > creds->uid) do_shm = false;
> > > > 
> > > >      }
> > > > 
> > > > #endif
> > > > 
> > > > Maybe there's more stuff that needs to be changed as well,
> > > > I don't know.
> > > 
> > > Ok, so what about adding parameter which force SHM support
> > > if user/administrator/owner of system want to do that?
> > 
> > That sounds like a good idea.
> > 
> > It's a bit tricky to define the configuration syntax, though.
> > We currently have the "enable-shm" option in daemon.conf, and
> > that seems like the appropriate option to use here.
> > Currently, "no" means "no" and "yes" means "yes, if shm is
> > available and if we're not running in the system mode". We'd
> > need a third option that would have the semantics of "yes, if
> > shm is available". I don't know what the third option should
> > be named. I'd want "yes" to refer to the new option, and
> > introduce "user-mode-only" to refer to the current "yes", but
> > that's not a good choice, because we should keep the old
> > semantics attached to the old option values for compatibility
> > reasons. I suggest
> > "yes-also-in-system-mode" for the new option, but I really
> > hope someone comes up with something better.
> 
> Ok, then what about adding new option "enable-shm-in-system" (or 
> other name) which will be used for system mode and current option 
> "enable-shm" will be used only for user mode?

Yeah, maybe it's best to add another option. I'd suggest
"allow-shm-in-system-mode", which would control whether "enable-shm =
yes" has any effect in the system mode, but I don't feel too strongly
about this - I'd be ok with your suggestion too (I think the option
should say "system-mode" instead of just "system", though).

-- 
Tanu