On Fri, 2014-07-25 at 17:43 +0400, Sergey Klyaus wrote: > 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).
No to your third option. This is no USB problem. The issue is in the generic code. The only clean fix is your suggestion (2) Regards Oliver -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/