linux-kernel - Re: REGRESSION: usbdevfs: Use-scatter-gather-lists-for-large-bulk-transfers

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Date:	Sun, 14 Oct 2012 17:40:56 +0200
From:	Hans de Goede <hdegoede@...hat.com>
To:	Henrik Rydberg <rydberg@...omail.se>
CC:	Alan Stern <stern@...land.harvard.edu>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	Peter Stuge <peter@...ge.se>
Subject: Re: REGRESSION: usbdevfs: Use-scatter-gather-lists-for-large-bulk-transfers

Hi,


On 10/12/2012 05:08 PM, Henrik Rydberg wrote:
> Hi Alan,
>
>> Instead of introducing a new local variable, why not simply update
>> uurb->buffer?  That's what we do elsewhere in the code.
>
> It seemed fragile, due to these scary lines:
>
> 	if (is_in && uurb->buffer_length > 0)
> 		as->userbuffer = uurb->buffer;
> 	else
> 		as->userbuffer = NULL;
>
> I suppose it works in this particular case.  How is the
> USBDEVFS_URB_TYPE_CONTROL case supposed to work here?
>
> I can certainly change the patch if preferred. Tested and attached
> below.
>
> Thanks,
> Henrik
>
>  From 40b70394747eea51fdd07cc8213dd6afd24b1b30 Mon Sep 17 00:00:00 2001
> From: Henrik Rydberg <rydberg@...omail.se>
> Date: Thu, 11 Oct 2012 23:27:04 +0200
> Subject: [PATCH v2] usbdevfs: Fix broken scatter-gather transfer
>
> The handling of large output bulk transfers is broken; the same u
> page is read over and over again. Fixed with this patch.
>
> Signed-off-by: Henrik Rydberg <rydberg@...omail.se>
> ---
>   drivers/usb/core/devio.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
> index ebb8a9d..6e58b59 100644
> --- a/drivers/usb/core/devio.c
> +++ b/drivers/usb/core/devio.c
> @@ -1349,6 +1351,7 @@
>   					goto error;
>   				}
>   			}
> +			uurb->buffer += u;

I know you've already fixed this in the next revision, but still:

NAK, this will break large, split input transfers as it well
set as->userbuffer to the end of the buffer instead of the beginning!

Regards,

Hans
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