A USB-serial converter device is plugged into a system, and a process
opens it's device node. If the device is physically removed whilst the
process still has its device node open, then other processes can
sucessfully open the now non-existent device's node. I would expect
that open() on a device that has been physically removed should return
ENODEV.
This is manifesting itself with getty on my system. I do the following:
1. set up inittab to spawn getty on ttyUSB0, eg:
T1:23:respawn:/sbin/getty -L ttyUSB0 115200 vt100
2. Plug in USB-serial converter cable
3. Wait for a login prompt on a terminal program attached to the serial
cable
4. Login
5. Pull the USB-serial converter cable from the box
6. getty doesn't realise that ttyUSB0 no longer exists as /dev/ttyUSB0
can still be opened.
7. Re-insert the USB-serial converter cable
8. You should no longer get a login prompt over the serial cable, as
the the USB-serial cable now shows up as /dev/ttyUSB1, and getty is
trying to talk to /dev/ttyUSB0.
The attached patch will cause open("/dev/ttyUSB0", O_RDONLY) to return
ENODEV after the USB-serial converter has been pulled. The patch was
created against 2.6.28.1. I can supply it against something else if
needs be. It is fairly simple, so should be OK.
I am using a pl2303 device, although I don't think that makes any
difference.
From: James Woodcock <James.Woodcock@ACULAB.COM>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
James Woodcock