Re: [linux-usb-devel] USB/hal: USB open() broken? (USB CD burner underruns, USB HDD hard resets)

[Andreas Mohr <andim2@users.sourceforge.net>]

Hi,

On Wed, Jun 21, 2006 at 12:15:08PM -0400, Alan Stern wrote:
> On Wed, 21 Jun 2006, Andreas Mohr wrote:
> > - TEST_UNIT_READY
> > - TEST_UNIT_READY
> > - READ_TOC (failure?)
> 
> I don't know why this failed.  Maybe the disc didn't have a valid Table of 
> Contents.

Ah, silly me, I should have stated that this was a simulation burn on an
otherwise rather blank disc ;)


> > - WRITE_10 (ok!)
> > - ALLOW_MEDIUM_REMOVAL (ok!)
> > - WRITE_10 (*** FAILURE! ***)
> > - going downhill from here...
> > 
> > 
> > So what could be the problem here?
> > READ_TOC might be it, but then it might be fully ok to have it fail
> > (after all it's non-valid data content), so ALLOW_MEDIUM_REMOVAL would be the
> > problem then? (next WRITE_10 FAILS!).
> 
> It sure does look like the ALLOW_MEDIUM_REMOVAL is the cause of the 
> problem.

Yup, already was quite sure of that after having written the previous mail.

I'll try to verify this by simply removing all ALLOW_MEDIUM_REMOVAL calls ;)


> > I could be totally wrong, though, since I don't have much storage debugging
> > experience.
> > 
> > 
> > A good idea would be to further check whether it's the open() or the close()
> > which disrupts burning for me.
> 
> Yep.  The ALLOW_MEDIUM_REMOVAL occurs as part of handling the close().  
> And you can understand a CD drive not wanting to carry out a long write 
> when the door is unlocked.
> 
> The real problem seems to be that the device is reachable in two different 
> ways, and they don't implement proper mutual exclusion.  HAL (or your test 
> program) is undoubtedly using /dev/sr0 or something similar, whereas 
> cdrecord uses /dev/sg0.  Going through two different drivers, it's no 
> surprise they wind up interfering with each other.

HAL is /dev/host0/.../cd
cdrecord is -dev=0,0,0 (whatever Linux device file this translates into)
or a similar device ID as returned by -scanbus.


Probably (stating the obvious here, I'm afraid) we should only send
non-ALLOW_MEDIUM_REMOVAL for the *very first* device open,
and then send ALLOW_MEDIUM_REMOVAL after the *very last* device close only.

So you think that with sr and sg drivers both talking to the device,
proper inter-driver device tracking is not doable or quite difficult
to implement?


> Unfortunately I can't debug this without seeing the start of the oops 
> message.

[OOPS output of a *different* issue]

Right, it's a rather incomplete OOPS. Let me try to get one with a nice
long-line VGA mode soon...

Thanks!

Andreas Mohr
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