Re: Accessing usb devices with USBDEVFS

[Greg KH <greg@kroah.com>]

On Mon, May 01, 2006 at 11:39:11AM -0400, Danny Budik wrote:
> Kay Sievers wrote:
> >On Fri, Apr 28, 2006 at 01:44:08PM -0400, Danny Budik wrote:
> >  
> >>I have a question that may or may not be related to hotplugging. I have 
> >>noticed that when I plug in a USB device, it takes about 5 seconds for 
> >>it to show up in /proc/bus/usb/001/xxx. I am using HAL to recognize when 
> >>a USB device is plugged in and USBDEVFS to communicate with my device.
> >>
> >>When I plug it in, dbus/HAL instantly recognizes it and sends me a 
> >>message.  But when I make the function call to open it (using fopen on 
> >>the file above) I get an error that the device is not found. In fact, it 
> >>takes about 5 seconds for the device to show up in the /proc/bus/usb/ 
> >>directory so I have to place a sleep(5) line in my C code before I am 
> >>able to open the device.
> >>
> >>My test machine is a PIII 733 with FC4, latest kernel, so it is a 
> >>relatively slow machine. Is there a way to predict the time that it 
> >>takes for the device to be accessible with USBDEVFS so that I don't have 
> >>to hardcode the sleep statement?
> >>    
> >
> >Recent systems don't use /proc for usb access anymore and real device
> >nodes in /dev/bus/usb instead. HAL sends "usbraw" device anouncements with
> >"linux.device_file" as a property when the device is created.
> >
> >Kay
> So is there a way then to read from the /dev/bus/usb? Like I mentioned 
> in the parent post, I am just using fopen, and the functions provided in 
> usbdevice_fs.h and usb.h to read data from the usb device. The device is 
> a proprietary sensor that my company makes. Is there a 
> manual/documentation about how to do this the more "modern" way?

No, that's still the correct way.  If you use libusb, none of your code
changes at all.   If you are using "raw" usbfs, then just open a
different file.

Hope this helps,

greg k-h


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