[systemd-devel] [alsa-devel] [PATCH] alsa-restore.rules: refer to correct attr

[Takashi Iwai]

At Sun, 12 Jan 2014 11:39:29 -0500,
Dave Reisner wrote:
> 
> On Sun, Jan 12, 2014 at 11:15:52AM -0500, Dave Reisner wrote:
> > $attr{number} in the RUN rule is an empty expansion. This makes sense,
> > because the path doesn't exist -- i.e., it refers to the path:
> > 
> > /sys/devices/pci0000:00/foo/bar/sound/card0/controlC0/number
> > 
> > Instead, refer to $attr{device/number}, which does exist.
> > 
> > Signed-off-by: Dave Reisner <dreisner at archlinux.org>
> > ---
> > This seems to have been broken when it was first introduced a little over
> > three years ago (de7c3eff0e).
> 
> I dug into this a little more to figure out why this potentially *would*
> have worked and found the following advice from udev(7) about $attr{}:
> 
>   If the matching device does not have such an attribute, and a previous
>   KERNELS, SUBSYSTEMS, DRIVERS, or ATTRS test selected a parent device,
>   then the attribute from that parent device is used.
> 
> So, knowing how RUN expansions work, the simple presence of the
> following rule causes $attr{number} to expand properly
> 
>   SUBSYSTEM=="sound", ATTRS{id}=="M2496"
> 
> I named this /etc/udev/rules/91-alsa-foo.rules -- intentionally after
> the restore rule.
> 
> Of course, this specifically matches my system, but one could imagine
> a more general rule which would cause parent matches and thus change the
> behavior of the subsequent $attr{number} expansion. I'm not sure if this
> is intended behavior in udev since the parent match doesn't occur in the
> same rule.
> 
> So, $attr{number} is potentially correct (but this seems weird), while
> $attr{device/number} should always be correct.
> 
> Hope this makes sense...

Yeah, $attr{device/number} looks definitely better.
I applied the patch now.  Thanks.


Takashi

> 
> > Please CC me on replies as I am not subscribed to the list.
> > 
> >  alsactl/90-alsa-restore.rules.in | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/alsactl/90-alsa-restore.rules.in b/alsactl/90-alsa-restore.rules.in
> > index 88e12e0..c68119d 100644
> > --- a/alsactl/90-alsa-restore.rules.in
> > +++ b/alsactl/90-alsa-restore.rules.in
> > @@ -2,7 +2,7 @@ ACTION=="add", SUBSYSTEM=="sound", KERNEL=="controlC*", KERNELS!="card*", GOTO="
> >  GOTO="alsa_restore_end"
> >  
> >  LABEL="alsa_restore_go"
> > -TEST!="@daemonswitch@", RUN+="@sbindir@/alsactl restore $attr{number}"
> > -TEST=="@daemonswitch@", RUN+="@sbindir@/alsactl nrestore $attr{number}"
> > +TEST!="@daemonswitch@", RUN+="@sbindir@/alsactl restore $attr{device/number}"
> > +TEST=="@daemonswitch@", RUN+="@sbindir@/alsactl nrestore $attr{device/number}"
> >  
> >  LABEL="alsa_restore_end"
> > -- 
> > 1.8.5.2
> > 
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