linux-kernel - Re: [PATCH v4] usbip: Don't submit special requests twice

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Date: Sun, 05 May 2024 19:54:36 +0200
From: "Simon Holesch" <simon@...esch.de>
To: "Hongren Zheng" <i@...ithal.me>
Cc: "Valentina Manea" <valentina.manea.m@...il.com>, "Shuah Khan"
 <shuah@...nel.org>, "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
 "Shuah Khan" <skhan@...uxfoundation.org>, <linux-usb@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] usbip: Don't submit special requests twice

On Sun May 5, 2024 at 5:31 PM CEST, Hongren Zheng wrote:
> On Sun, Dec 17, 2023 at 08:30:40PM +0100, Simon Holesch wrote:
> > Skip submitting URBs, when identical requests were already sent in
> > tweak_special_requests(). Instead call the completion handler directly
> > to return the result of the URB.
>
> Reproduced the behavior and this patch fixed the bahavior

Thank you for testing.

> > @@ -468,6 +477,7 @@ static void stub_recv_cmd_submit(struct stub_device *sdev,
> >  	int support_sg = 1;
> >  	int np = 0;
> >  	int ret, i;
> > +	int is_tweaked;
> >  
> >  	if (pipe == -1)
> >  		return;
> > @@ -580,8 +590,7 @@ static void stub_recv_cmd_submit(struct stub_device *sdev,
> >  		priv->urbs[i]->pipe = pipe;
> >  		priv->urbs[i]->complete = stub_complete;
> >  
> > -		/* no need to submit an intercepted request, but harmless? */
> > -		tweak_special_requests(priv->urbs[i]);
> > +		is_tweaked = tweak_special_requests(priv->urbs[i]);
>
> One question though, if there are mutiple urbs and one of them is
> SET CONFIGURATION, then all of them would not be submitted,
> as is_tweaked is a *global* flag instead of a per-urb flag.
>
> Now it is assumed that when the urb is SET CONFIGURATION then
> num_urbs is 1. I assume it just happens to be the case and I do
> not know if it holds for all scenario.

To be honest, I didn't fully understand the num_urbs > 1 case. I assumed
this is for drivers not supporting SG and a long URB is just broken up
into multiple ones.