Re: [PATCH]generic usb serial driver

On Fri, Mar 30, 2007 at 06:08:44PM +0200, Oliver Neukum wrote:
> Am Freitag, 30. M?rz 2007 17:41 schrieb Greg KH:
> > On Fri, Mar 30, 2007 at 11:17:28AM +0200, Oliver Neukum wrote:
>  
> > > However it would not always work out so nicely.
> > > Have a look at this code from usblp:
> > > 
> > > 			timeout = USBLP_WRITE_TIMEOUT;
> > > 
> > > 			rv = wait_event_interruptible_timeout(usblp->wait, usblp->wcomplete || !usblp->present , timeout);
> > > 			if (rv < 0)
> > > 				return writecount ? writecount : -EINTR;
> > 
> > Well, usblp incorrectly (in my opinion) tries to return the status of
> > every urb to userspace.  I'm still not quite sure why it needs to do
> > that, and we can't just throw a ton of urbs at the device and then walk
> > away.  It's not like userspace does much if we report an error on the
> > exact packet that fails, vs a packet later on, right?
> 
> I can't tell you whether cups closes the device for every job.
> But it does not matter. Keeping it open is fully legitimate. You must
> know which urb has failed to know whose print job has failed.

Ah, hm, good point, forgot about that :(

> [..]
> > I think it really comes down to the problem of checking the urb status
> > flag.
> 
> Only for the write case. Reading needs the transfer_buffer.
> mdc800 has exactly that race. You are looking for a work around now.

If you need the transfer_buffer then use a lock.

> > I _REALLY_ want to get rid of that field and not have drivers us it at
> > all.  I would like to pass the value of the status flag to the urb
> > callback directly, and only have the status field be used by the host
> > controllers.
> 
> Good idea in any case.
> 
> > The last time I looked into implementing this, I think the UHCI driver
> > had some 'issues' with how it would work, or maybe it was EHCI, sorry it
> > was a few years ago.
> > 
> > However, if we are able to fix that, and never let drivers touch that
> > field, then the large majority of these kinds of problems will go away,
> > right?
> 
> I haven't counted them. I guess it is safe to say that many issues
> would go away.

So, would you possibly be willing to look into this if you have the
chance?

thanks,

greg k-h

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