I sent this message off a week ago (June 8th) and received no reply. Looks like the mailing list is being spammed, so I suppose it could've been missed.
My concern is: What happens when a user process has a USB serial device (e.g. /dev/ttyUSB0) open and the USB cable is unplugged. Right now, the process receives no signal, no EIO from the read() or select(), and has no means of identifying that the hardware connection is gone.
Furthermore, when the cable is plugged back in, the system allocates /dev/ttyUSB1 for its use as long as the process still has ttyUSB0 opened.
Is there any way I can identify when a USB cable is unplugged within the process, without using an external watchdog program that monitors sysfs?
Thanks, -Byron
-- Byron Stanoszek Ph: (330) 644-3059 Systems Programmer Fax: (330) 644-8110 Commercial Timesharing Inc. Email: [EMAIL PROTECTED]
---------- Forwarded message ---------- Date: Tue, 8 Jun 2004 11:49:51 -0400 (EDT) From: Byron Stanoszek <[EMAIL PROTECTED]> To: [EMAIL PROTECTED], [EMAIL PROTECTED] Subject: Behavior of serial usb driver when unplugged
Hi all,
I'm currently using Linux (2.6.7-rc3) in an embedded system with a 8-port Sealevel SeaLink 2802 USB device. This is a 8-port RS-232/422 device that allocates /dev/ttyUSB0 through /dev/ttyUSB7 when plugged in.
If I have a process talking to one of the ports, e.g. 'cat < /dev/ttyUSB0', and I unplug the USB hub, all ports except ttyUSB0 unregister properly.
Without killing the 'cat' process, plugging the hub back in will make it allocate /dev/ttyUSB1 through /dev/ttyUSB8, thereby offsetting each USB port# by 1.
When killing the 'cat' process at this point, the kernel reports:
drivers/usb/serial/ftdi_sio.c: error from flowcontrol urb drivers/usb/serial/ftdi_sio.c: Error from DTR LOW urb drivers/usb/serial/ftdi_sio.c: Error from RTS LOW urb
and then unregisters /dev/ttyUSB0.
Is there a way to allow "hotplug" of a USB device to reuse /dev/ttyUSB0 regardless if an application still has that particular tty open?
If not, is there a way I could make the serial subsystem can send an EIO errno or some other notification when the serial device is disconnected?
Thanks for your help, -Byron
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