linux-kernel - Re: gadgetfs: how to wait for USB device initialization?

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Message-ID: <CAFDyS3P3S9U_KhMBLvS1GanzprY09rsuDbstB8B7-vaASwVKzA@mail.gmail.com>
Date:   Tue, 13 Jun 2017 19:02:10 +0300
From:   Tal Shorer <tal.shorer@...il.com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Elena Reshetova <elena.reshetova@...el.com>,
        USB list <linux-usb@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller <syzkaller@...glegroups.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>
Subject: Re: gadgetfs: how to wait for USB device initialization?

On Tue, Jun 13, 2017 at 3:21 PM, Andrey Konovalov <andreyknvl@...gle.com> wrote:
> Hi!
>
> I'm trying to use gadgetfs to fuzz USB device drivers by simply
> connecting random devices for now.
>
> What I want to achieve right now is the following:
>
> 1. mount gadgetfs
> 2. emulate connection of a new USB device
> 3. wait for the device to finish initializing
> 4. unmount gadgetfs
> 5. goto 1
>
> The question is how do I wait for the device to finish initializing
> (the corresponding USB driver to finish probing?) before unmounting
> gadgetfs? As I understand, when I write device description to
> "/dev/gadget/dummy_udc" the initialization happens asynchronously
> after writing is done.
>

You can use inotify on the state file inside a udc's sysfs directory.
It's awesome like that.
Here's a sample code that doesn't do any cleanups because I'm lazy:
https://gist.github.com/talshorer/61be1bc3472cc2a7b4866b9bd5a239ca