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

[Noboru Iwamatsu <n_iwamatsu@xxxxxxxxxxxxxx>]

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@xxxxxxxxxxxxx>
>
> 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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