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List:       linux-hotplug
Subject:    Re: Accessing usb devices with USBDEVFS
From:       Kay Sievers <kay.sievers () vrfy ! org>
Date:       2006-04-29 13:06:08
Message-ID: 20060429130608.GB13319 () vrfy ! org
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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


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