Messages in this thread | | | Date | Mon, 29 Sep 2008 22:12:58 -0700 | From | Greg KH <> | Subject | Re: help finding entry point of USB data in the kernel, not drivers/usb/core/devio.c? |
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On Tue, Sep 30, 2008 at 01:04:26AM -0400, George Nychis wrote: > Hi all, > > I am trying to find the entry point of USB data in the kernel. I have a > USB device and I would like to find the latency between the time the data > enters the kernel, and I read it in userspace. My first goal is to find > where it actually enters the kernel.
I suggest asking this on the linux-usb mailing list instead, it would reach the main Linux USB developers.
> The host device driver obtains a URB and reads the data from urb->buffer.
Wait, which way are you sending this data? To or from the device?
> From digging around the kernel code, I had assumed the entry point for all > USB data was in drivers/usb/core/devio.c::usbdev_read() ... but it seems as > though that is not the case.
No, that entry point is for usbfs, not the individual drivers, and not the core.
> Right after the device is locked in this function, I added a simple printk: > printk("Reading %d bytes\n", nbytes); // Line 135 > > Then around line 154 after it reads the usb device descriptor, I added: > if(temp_desc.idVendor==0xfffe && temp_desc.idProduct==0x0002) { > printk("...Data from USRP\n"); > } > > That gives me an idea that the data is coming from the device I am looking > for. > > But, it seems as though this method is only related to control information > to/from the USB device? Whenever I start my application, I get about 1614 > total bytes read from my first printout, and I see only one of my second > printout messages. Whereas, I am reading a total of about 8MB from the USB > device over the period of time. So I think I am completely missing my > actual data entry point.
Are you watching all of the different USB device endpoints?
thanks,
greg k-h
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