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SubjectRe: 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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