[pulseaudio-discuss] --check option seems not to work from su(1) as daemon user

[Tanu Kaskinen]

On Sat, 2014-08-23 at 08:41 -0600, Glenn Golden wrote:
> Tanu, Felipe,
> 
> Writing up some text now for the --check option. Further below is what I have
> so far. A lot longer than the original, but it attempts to cover everything
> that has been mentioned in the thread thus far.
> 
> However, while verifying some of the statements made in the proposed text (by
> doing experiments with $XDG_RUNTIME_DIR and $HOME settings and looking at debug
> output) I found some discrepancies between the experiment results and some
> statements made earlier in the thread. Can you comment on these please:
> 
> 1.  > ...if XDG_RUNTIME_DIR isn't set at all, then the check assumes that
>     > HOME[1] is set correctly.
> 
>     The experiments seem to indicate that if XDG_RUNTIME_DIR is EITHER unset 
>     OR if it points to a directory or pid file which is inaccessible or non-
>     existent, then the $HOME approach is used.

That's surprising to me. Falling back to $HOME if $XDG_RUNTIME_DIR is
set but doesn't work doesn't seem like a good idea.

> 2.  In the latter case ($HOME approach) it seems that on my system (Arch linux)
>     the directory in which the xxxx-runtime file is located is not
>     $HOME/.config/pulse (as was stated earlier in the thread), but $HOME/.pulse.
>     Are there any other possibilities?

$HOME/.pulse is the old location. It's still used if it exists, to not
lose old user preferences.

> 3.  Also pertaining to the $HOME approach, in which the runtime dir is named
>     as "xxxx-runtime", where xxxx is a hex string: I'd like to at least say
>     a few words about what that "xxxx" is. Is it a per-session ID? Or per-seat?
>     Or what?

It's the machine-id (defined in /etc/machine-id). The reason for having
that in the file name is that the home directory may be on a network
file system, and used on multiple machines simultaneously. With the
machine-id prefix, PulseAudio running on machine A will see a different
set of files than PulseAudio running on machine B, so they don't
conflict with each other.

If /etc/machine-id doesn't exist, then the hostname is used as the
prefix instead.

> 4.  Even better than answering 1-3: Do you know of any extant PulseAudio doc
>     that could be cited which describes in detail the way in which the
>     combination of
> 
> 	- $XDG_* envars
>         - "standard" envars ($HOME, e.g.)
>         - OS/installation conventions
> 
>     interact to lead to the sequence of candidate paths for the runtime
>     directory when the daemon starts?

No, there's no such document. I suppose it wouldn't be a bad idea to
have a page in the wiki about the different files that PulseAudio uses,
and how they are located. I can give you write access to the wiki if you
wish (for spam reasons, the freedesktop.org wiki doesn't allow random
people to register themselves).

>     If such a document exists, then the
>     --check option blurb could avoid the need to lay it all out in gory detail
>     and simply say something like "The process ID of the daemon to be queried
>     is determined in accordance with [1]", and then add a REFERENCES subsction
>     to the man page and list [1] as that extant doc.
> 
> In the absence of any such extant detailed doc, I honestly don't see any way
> to accurately and usefullly describe the operation of --check without including
> that detail in the blurb itself, as is done below.  Anything less just leaves
> opportunity for confusion.
> 
> Anyway...  here's what I have so far. Text in square brackets is meta-stuff.
> =============================================================================
> --check
> 
>   Attempts to query a running PA daemon

This sounds like --check will attempt to connect to the daemon, which it
doesn't do. I suggest: "Checks whether a PulseAudio daemon is currently
running for the calling user (but see limitations below). The exit code
is zero if there's a daemon running."

Then explain the limitations, i.e. the current implementation relies on
a pid file, and locating that requires $XDG_RUNTIME_DIR or $HOME to
match the environment of the running daemon (an explicit warning about
su/sudo not updating $XDG_RUNTIME_DIR would be good).

-- 
Tanu