[nSLUG] DVD drive with no CD audio (and now udev)

Rich budman85 at eastlink.ca
Thu Feb 5 16:06:08 AST 2009



Mike Spencer wrote:
> me> Just bought a DVD drive....an ordinary audio CD produces no sound. 
>
> To which Daniel Morrison <draker at gmail.com> replied:
>
>   
>> Uh, Mike, you asked this same question here:
>> http://nslug.ns.ca/pipermail/nslug/2008-October/011954.html
>>
>> And I said: there should be an analog CD audio cable.  
>>
>> And Aaron Spanik said: 
>> "most of the CD/DVD drives you buy today no longer even
>> have that connector on the back"...so you must do this digitally.
>>     
>
> Quite right. Ah, well, the problem here is with memory, not with
> thinking.
>
> See, in the previous case (if you rooted through the whole thread, you
> will have seen that) the problem was the missing 4-pin audio cable.  I
> found one, plugged it in and had audio.  When the cable fixed me up, I
> promptly forgot all the hard but then-unneeded stuff, especially
> considering that, about the same time, a new Philips DVD drive had
> worked as expected out of the box on a (even older) PIII.
>
> The new LG drive *does* have the same 4-pin analog audio output
> connector on the back so I reasonably expected it to be functional.
> Now that I'm reminded by Rich that "many of the new drives use the IDE
> interface to send the audio signal", I've groveled through the
> marketing bumpf returned by google and found a manual from lge.com.
> Right: There *is* a 4-pin analog audio plug but it's "not supported",
> i.e., as my rural neighbors say, it's as "useless as tits on a boar
> pig."
>
> This sounds like another "WinModem" deal.
>
> But this box has *two* CD-type drives.  So last night I re-installed
> the audio-crippled DVD drive but plugged the analog audio cable into
> the other, older drive.  Yow!  Audio CDs play fine.  So I re-jiggered
> /etc/fstab and ~/.alias, created some symlinks like /dev/dvd ->
> /dev/hdc and /dev/cdrom -> /dev/sr0.
>
> [Sound over: ominous music, distant thunder, faint cries of rage off...]
>
> But when I re-booted today, JHFC, something -- udev, I assume -- has
> "fixed" all that for me, reorganizing /dev to suit itself: /dev/dvd is
> gone, /dev/cdrom now points once again to /dev/hdc.  Both /etc/fstab
> and several aliases that reference the CD drives are now meaningless.
>
> WTF?!!  How do I reclaim control of symlinks in /dev?  Do I have to
> learn the (apparently messy or at least tedious) semantics for writing
> udev rules and edit files in /etc/udev/rules.d?  Add "ln -s" lines to
> rc.local?  Or is reinstallation without udev (if that's even possible)
> the only way to create symlinks in /dev to suit myself?
>
>   
:) had the same thing when udev was introduced

You need to create local rules file in /etc/udev/rules.d

Example of my setup

File:   10-local.rules

SUBSYSTEMS=="scsi",KERNEL=="sd?1",ATTRS{model}=="USB CF Reader   
",SYMLINK+="cardCF"
SUBSYSTEMS=="scsi",KERNEL=="sd?1",ATTRS{model}=="USB MS Reader   
",SYMLINK+="cardMS"
SUBSYSTEMS=="scsi",KERNEL=="sd?1",ATTRS{model}=="USB SM Reader   
",SYMLINK+="cardSM cardXD"
SUBSYSTEMS=="usb",KERNEL=="sd?1",ATTRS{product}=="USB2.0 Card 
Reader",SYMLINK+="cardSDHC"

SUBSYSTEMS=="scsi",ATTRS{vendor}=="UMAX",ATTRS{model}=="Astra 
2200",SYMLINK+="scanner"

To get the info for SUBS, KERNEL, and ATTRS values:

Slack12.1
udevinfo -a -p `udevinfo -q path -n /dev/sdd`

Slack 12.2
udevadm info -a -p `udevadm info -q path -n /dev/sdd`

Long version:
udevadm info --attribute-walk --path `udevadm info --query path --name 
/dev/sdd`

SYMLINK - sets the link in /dev

For a cd player
SUBSYSTEMS=="ide",KERNEL=="hda",ATTRS{media}=="cdrom",SYMLINK+="cdrom"

I can use any of these in the matching items
    DRIVERS=="ide-cdrom"
    ATTRS{media}=="cdrom"
    ATTRS{drivename}=="hda"
    ATTRS{modalias}=="ide:m-cdrom"
    ATTRS{model}=="HL-DT-ST DVDRAM GSA-4163B"
    ATTRS{firmware}=="A104"

There are some really good udev tutortials.
Its not hard once you know what you are looking for.
Think of it as uniquely matching the device info, then doing something 
with it.



Rich
> I 
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