netdev - Re: [usb regression] Re: [PATCH 2.6.24-rc3] Fix /proc/net breakage

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Date:	Sun, 30 Dec 2007 21:25:00 -0800
From:	Greg KH <greg@...ah.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Andreas Mohr <andi@...as.de>, Ingo Molnar <mingo@...e.hu>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Woodhouse <dwmw2@...radead.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Pavel Machek <pavel@....cz>,
	kernel list <linux-kernel@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>,
	Pavel Emelyanov <xemul@...nvz.org>,
	"Denis V. Lunev" <den@...nvz.org>
Subject: Re: [usb regression] Re: [PATCH 2.6.24-rc3] Fix /proc/net breakage

On Sun, Dec 30, 2007 at 03:34:45PM -0500, Alan Stern wrote:
> On Sun, 30 Dec 2007, Ingo Molnar wrote:
> 
> > * Andreas Mohr <andi@...as.de> wrote:
> > 
> > > (yes, that's all there is, despite CONFIG_USB_DEBUG being set)
> > > 
> > > The LED of a usb stick isn't active either, for obvious reasons.
> > > 
> > > And keep in mind that this is a (relatively old) OHCI-only machine... 
> > > (which had the 2.6.19 lsmod showing ohci-hcd just fine and working 
> > > fine with WLAN USB)
> > > 
> > > Now pondering whether to try -rc6 proper or whether to revert specific 
> > > guilty-looking USB changes... And wondering how to properly elevate 
> > > this issue (prompt Greg about it, new thread, bug #, ...?)
> 
> It looks like Greg misused the debugfs API -- which is ironic, because
> he wrote debugfs in the first place!  :-)

Oh crap, sorry, I did mess that up :(

> Let me know if this patch fixes the problem.  If it does, I'll submit 
> it to Greg with all the proper accoutrements.

This isn't going to work if CONFIG_DEBUGFS is not enabled either :(

> Index: 2.6.24-rc6-mm1/drivers/usb/host/ohci-hcd.c
> ===================================================================
> --- 2.6.24-rc6-mm1.orig/drivers/usb/host/ohci-hcd.c
> +++ 2.6.24-rc6-mm1/drivers/usb/host/ohci-hcd.c
> @@ -1067,14 +1067,8 @@ static int __init ohci_hcd_mod_init(void
>  
>  #ifdef DEBUG
>  	ohci_debug_root = debugfs_create_dir("ohci", NULL);
> -	if (!ohci_debug_root || IS_ERR(ohci_debug_root)) {
> -		if (!ohci_debug_root)
> -			retval = -ENOENT;
> -		else
> -			retval = PTR_ERR(ohci_debug_root);
> -
> -		goto error_debug;
> -	}
> +	if (!ohci_debug_root)
> +		return -ENOENT;

It needs to check for ERR_PTR(-ENODEV) which is the return value if
debugfs is not enabled, and if so, just ignore things.

If NULL is returned, or anything else, it's a real error.

So, try something like:
	if (!ohci_debug_root) {
		retval = -ENOENT;
		goto error_debug;
	}
	if (IS_ERR(ohci_debug_root) && PTR_ERR(ohci_debug_root) != -ENODEV) {
		retval = PTR_ERR(ohci_debug_root);
		goto error_debug;
	}

and let me know of that works for you.

Although the combination of CONFIG_USB_DEBUG and not CONFIG_DEBUGFS is
strange, we could just enable CONFIG_DEBUGFS is USB_DEBUG is enabled and
then simplify this logic a bunch at the same time.

thanks,

greg k-h
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