Re: [PATCH] usbfront: do not assume sequentially mapped pages

[Noboru Iwamatsu <n_iwamatsu@jp.fujitsu.com>]

Hi,

Oh, I had a misunderstanding about the continuity of buffer pages.
This caused webcam's image to corrupt.

PVUSB applied to this change can work well with the following webcams.

* Creative Labs: WebCam 3 USB (with ov511 driver)
* Creative Labs: WebCam NX pro (with gspca driver)

Now, Webcam works!

Thanks,

Noboru

Ian Jackson wrote:
> xenhcd_gnttab_map in usbfront-q.c looks up the mfn of the start of the
> usb transfer buffer.  But the buffer may span several pages, and the
> current code simply increments the obtained mfn.  Needless to say this
> is an unwarranted assumption.  It causes large transfers to be
> corrupted and/or to overwrite other parts of memory.
> 
> Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
> 
> diff -r 87c84f7dd850 drivers/xen/usbfront/usbfront-q.c
> --- a/drivers/xen/usbfront/usbfront-q.c	Fri Mar 20 09:00:58 2009 +0000
> +++ b/drivers/xen/usbfront/usbfront-q.c	Fri Mar 27 17:53:12 2009 +0100
> @@ -106,12 +106,15 @@ static inline void xenhcd_gnttab_map(str
>  	unsigned int bytes;
>  	int i;
>  
> -	page = virt_to_page(addr);
> -	buffer_pfn = page_to_phys(page) >> PAGE_SHIFT;
> -	offset = offset_in_page(addr);
>  	len = length;
>  
>  	for(i = 0;i < nr_pages;i++){
> +		BUG_ON(!len);
> +
> +		page = virt_to_page(addr);
> +		buffer_pfn = page_to_phys(page) >> PAGE_SHIFT;
> +		offset = offset_in_page(addr);
> +
>  		bytes = PAGE_SIZE - offset;
>  		if(bytes > len)
>  			bytes = len;
> @@ -123,9 +126,8 @@ static inline void xenhcd_gnttab_map(str
>  		seg[i].offset = (uint16_t)offset;
>  		seg[i].length = (uint16_t)bytes;
>  
> -		buffer_pfn++;
> +		addr += bytes;
>  		len -= bytes;
> -		offset = 0;
>  	}
>  }
>  
> 
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