linux-kernel - Re: 2.6.31-rc3: replugging USB serial converter uses new device node

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Date:	Thu, 23 Jul 2009 17:11:12 +0200
From:	Kay Sievers <kay.sievers@...y.org>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ferenc Wagner <wferi@...f.hu>, linux-kernel@...r.kernel.org,
	alan@...rguk.ukuu.org.uk, linux-usb@...r.kernel.org
Subject: Re: 2.6.31-rc3: replugging USB serial converter uses new device node

On Thu, Jul 23, 2009 at 16:44, Alan Stern<stern@...land.harvard.edu> wrote:
> On Thu, 23 Jul 2009, Andrew Morton wrote:
>> On Sat, 18 Jul 2009 22:04:57 +0200 Ferenc Wagner <wferi@...f.hu> wrote:

>> > Since upgrading to 2.6.31-rc3 from 2.6.30, my ttyUSB device number
>> > keeps increasing on each replug.  Output of udevadm monitor:
> ...
>> > Dmesg is available at http://pastebin.com/d516e3e00.
>>
>> Can anyone say whether this is expected behaviour?
>
> It depends on whether a program is still holding the old device file
> open when the replug occurs.
>
>> Does it actually cause any observeable problems?  I expect things will
>> get ugly once it runs out of range.
>
> The numbers will get reused after the corresponding device files are
> closed.

You might find a symlink for ttyUSB devices to the actual device node,
which does not depend on the kernel name, in:
  /dev/serial/
  |-- by-id
  |   `-- usb-067b_2303-if00-port0 -> ../../ttyUSB0
  `-- by-path
      `-- pci-0000:00:1d.7-usb-0:1.1.3.2:1.0-port0 -> ../../ttyUSB0

> For further discussion, see this thread:
>
>        http://marc.info/?t=124828810800002&r=1&w=2

I can't find the original message to reply, but the device node is
always deleted and re-created when the device goes away and comes
back.

Thanks,
Kay
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