Re: [PATCH 36/78] USB: add power/level sysfs attribute
Alan Stern <[email protected]>
| Newsgroups | gmane.linux.usb.devel |
|---|---|
| Message-ID | <[email protected]> |
On Sat, 28 Apr 2007, Oliver Neukum wrote: > > In other words, one user can force a device to suspend while another user > > is trying to access the device. True enough. The second user will get > > I/O errors. > > Will he? What happens if you submit an URB for a suspended device? Well, of course there's a race. :-) If the URB is submitted before the device is marked as suspended, it will be accepted and linked into the schedule. Then it will get low-level protocol errors when the device fails to respond to the packets sent by the host controller, so the URB will fail with -EPROTO or something similar. On the other hand (this is probably what you had in mind), if the URB is submitted _after_ the device is marked as suspended then usbcore won't accept it at all. usb_submit_urb() returns with -EHOSTUNREACH. Alan Stern ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ [email protected] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel