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 03:02:44PM -0400, Alan Stern wrote:
> On Wed, 21 Jun 2006, Andreas Mohr wrote:
> 
> > Maybe it's better to (additionally?) go down the route of fixing up
> > low-level communication weaknesses (since it's been semi-confirmed that it's
> > an USB communication issue, see other thread part).
> > IMHO this is a severe user experience issue that shouldn't be fixed up
> > ("covered", "hidden") by the O_EXCL thingy alone.
> 
> It's not a USB issue; it's a matter of lack of coordination between the sg 
> and sr drivers.  Each is unaware of the actions of the other, even when 
> they are speaking to the same device.

Right, I could have expressed it much better before, sorry.

Found the relevant code:
sd.c sd_open()

        if (!sdkp->openers++ && sdev->removable) {
                if (scsi_block_when_processing_errors(sdev))
                        scsi_set_medium_removal(sdev, SCSI_REMOVAL_PREVENT);
        }

And the obvious question would be whether the sdkp->openers++ thingy
could somehow be extended to enclose all hardware device users so that
e.g. sr.c wouldn't send ALLOW_MEDIUM_REMOVAL on a device already locked
by e.g. the sd.c driver.
Difficult question, though, since the group of drivers possible to use
with a certain device is not a static set:
it could be via
- sr.c
- sd.c
- IDE (in the case of ATA devices mapped via ide-scsi)
- ???

Is it possible to have such a per-*hardware*-device instance in the kernel
to keep track of various things such as number of device openers?
I'll do some investigation myself, too...

Thanks!

Andreas Mohr