linux-kernel - Re: [REGRESSION] cdrom drive doesn't detect removal

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Date:	Wed, 22 Sep 2010 09:38:05 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Maxim Levitsky <maximlevitsky@...il.com>
CC:	Kay Sievers <kay.sievers@...y.org>,
	Henrique de Moraes Holschuh <hmh@....eng.br>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Jens Axboe <axboe@...nel.dk>
Subject: Re: [REGRESSION] cdrom drive doesn't detect removal

Hello,

On 09/22/2010 01:09 AM, Maxim Levitsky wrote:
> I just did a strace on udisks, and it is pretty much self explanatory.
> (While CD is mounted).
> 
> open("/dev/sr0", O_RDONLY|O_EXCL|O_NONBLOCK) = -1 EBUSY (Device or resource busy)
> poll([{fd=5, events=POLLIN}, {fd=3, events=POLLIN}], 2, 1997) = 0 (Timeout)
> open("/dev/sr0", O_RDONLY|O_EXCL|O_NONBLOCK) = -1 EBUSY (Device or resource busy)
> poll([{fd=5, events=POLLIN}, {fd=3, events=POLLIN}], 2, 1997) = 0 (Timeout)
> open("/dev/sr0", O_RDONLY|O_EXCL|O_NONBLOCK) = -1 EBUSY (Device or resource busy)
> poll([{fd=5, events=POLLIN}, {fd=3, events=POLLIN}], 2, 1997) = 0 (Timeout)
> open("/dev/sr0", O_RDONLY|O_EXCL|O_NONBLOCK) = -1 EBUSY (Device or resource busy)
> 
> Sure, a filesystem is mounted, so exclusive access fails...
> 
> So, we end up with impossible to solve problem.  We want on one hand
> to guard the burner against polling programs that disturb it, but
> one the other hand we must do polling to check CD status.
>
> Unless the kernel does the polling, but then we also must stop it
> when burning is done.  I think that we need new ioctl in the CD
> driver that would give absolute access to the burning application,
> and lock it fully.

One thing I don't get is why the behavior changed after the claiming
block patch.  Can you please trace udisks from a previous working
kernel?

Thanks.

-- 
tejun
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