Hello.
I am currently working on a project with Thin clients with Citrix
Receiver 13 for Linux and encountered interesting problem with USB
device redirection.
ctxusb/ctxusbd process from Citrix Receiver are using inotify mechanism
to monitor /dev/bus/usb filesystem, and when device arrives, tries to
open it, but get ENODEV status:
Jul 25 11:36:13 myaut-desktop ctxusbd[2664]: Failed to open device: No
such device
Jul 25 11:36:13 myaut-desktop ctxusb[2751]: Failed to open device
001:003 (error 19 - No such device), bad id?
It is caused by design of device_add() function: it calls
devtmpfs_create_node before bus_add_device. Here are sequence of events:
1. device_add() calls devtmpfs_create_node(). That leads to inotify
event that.
2. ctxusb is awoken because inotify event arises, and calls ctxusbd daemon.
3. ctxusbd daemon opens /dev/bus/usb/new-device, so usbdev_open()
routine is called
4. usbdev_open() calls usbdev_lookup_by_devt(). Because device is not
yet attached to "usb bus", it returns NULL, and thus usbdev_open()
returns -ENODEV
5. Finally, device_add() calls bus_add_device(), and all subsequent
calls of usbdev_open() will succeed. However, ctxusb/ctxusbd already
reported an error and abandon device. User is unsatisfied.
I was able to reproduce that issue on Ubuntu 10.04 with 2.6.32 and 3.13
kernels.
However, it only occur on uni-processor systems (!)
I see three ways to solve that issue:
1. Leave it to userland applications (i.e. using loop with retries and
timeouts). However, I feel that it is a kernel issue (application is
notified before device is ready).
2. Call bus_add_device() before devtmpfs_create_node(). Very rough, and
probably breaks a lot of other kernel code.
3. Wait in usbdev_open() until reconfiguration is finished (i.e. by
using some global lock between usb_new_device() and usbdev_open(), or
add completion and special state USB_STATE_CONNECTING to a device).
P.S. Since I aren't subscribed to mailing list, could you add me in CC?
Thanks in advance.
Best Regards, Sergey.
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