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

[Alan Stern]

On Wed, 21 Jun 2006, Andreas Mohr wrote:

> > 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

That goes through the sr driver.

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

That goes through the sg driver.

> 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?

Well, it's not being done now.  I suspect it wouldn't be too difficult 
technically.  The hardest part might be to obtain the agreement of the 
SCSI and CDROM developers.  :-)

Alan Stern

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