linux-kernel - Re: help finding entry point of USB data in the kernel, not drivers/usb/core/devio.c?

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Date:	Mon, 29 Sep 2008 22:12:58 -0700
From:	Greg KH <greg@...ah.com>
To:	George Nychis <gnychis@....edu>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: help finding entry point of USB data in the kernel, not
	drivers/usb/core/devio.c?

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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