Re: usbmon, usb core, ARM

[Pete Zaitcev <zaitcev@redhat.com>]

On Thu, 20 Jan 2005 22:28:31 -0800, David Brownell <david-b@pacbell.net> wrote:

> By the way ... on the topic of usbmon rather than changing
> usbcore, is there a brief writeup of what you want this
> new version to be doing -- and how?  Like, why put the
> spy hooks in that location, rather than any of the other
> choices.  (Many of them would be less surprising to me!)

The main idea was to make usbmon invisible if it's not actively monitoring.
But after thinking about your message I see that it was a misguided approach.
I'm going to add "if (usbmon_is_running(bus)) usb_mon_hook(bus, urb);" into
hot paths instead, approximately where current suggestion comments are.

I cannot figure out if you understand the nature of the problem with current
usbmon, so let me restate it. Simply put, neither dev nor hcd are available
at the time urb->complete is called, and this is what usbmon intercepts.
For one thing, dev is down-counted in usb_unlink_urb(). This is why I tried
to find a way to avoid using them. Your "dev == hcd->self.root_hub" is
entirely out of question. But it's probably a moot point now anyway.

Adding hooks explicitly has its disadvantages. Although the giveback
path is much better, in the submit path such hook cannot inform usbmon
if the submission fails, and an additional hook is needed. Anyhow, you'll
see it all in the patch, please give me a couple of days.

Greetings,
-- Pete