linux-kernel - Re: [PATCH] EDD: Check for correct EDD 3.0 length

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Date:	Wed, 16 May 2012 11:28:41 +0300
From:	Gleb Natapov <gleb@...hat.com>
To:	Hannes Reinecke <hare@...e.de>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH] EDD: Check for correct EDD 3.0 length

On Wed, May 16, 2012 at 08:51:36AM +0200, Hannes Reinecke wrote:
> There are two competing EDD 3.0 specifications,
> the original one from Phoenix
> <http://mbldr.sourceforge.net/specsedd30.pdf>
> and the T-13 approved one
> <http://www.t13.org/documents/UploadedDocuments/docs2004/d1572r3-EDD3.pdf>
> 
> They differ in the length of the device_path field, which
> is one quad word for the Phoenix spec and two quad words
> for the T-13 spec. So we need to test for both lengths
> and blank out the second quad word when a Phoenix
> version is detected.
> 
Can you please clarify what practical problem are you seeing that
you are trying to fix with this patch?

> Signed-off-by: Hannes Reinecke <hare@...e.de>
> Cc: Gleb Natapov <gleb@...hat.com>
> Cc: H. Peter Anvin <hpa@...ux.intel.com>
> Cc: Alan Cox <alan@...rguk.ukuu.org.uk>
> 
> diff --git a/drivers/firmware/edd.c b/drivers/firmware/edd.c
> index e229576..beedf4c 100644
> --- a/drivers/firmware/edd.c
> +++ b/drivers/firmware/edd.c
> @@ -192,6 +192,13 @@ edd_show_interface(struct edd_device *edev, char *buf)
>  			p += scnprintf(p, left, " ");
>  		}
>  	}
> +	/*
> +	 * Phoenix EDD 3.0 reserves only one quad word for the
> +	 * device path, so blank out the second quad word.
> +	 */
> +	if (info->params.device_path_info_length == 36)
> +		info->params.device_path.unknown.reserved2 = 0;
> +
You overwrite checksum here. Hope it will not be checked after that point.
This will work for all interface types defined by Phoenix spec except
SCSI as far as I see. In Phoenix spec SCSI interface is one byte LUN,
in T13 it is changed to be: word SCSI ID, qword LUN.

>  	if (!strncmp(info->params.interface_type, "ATAPI", 5)) {
>  		p += scnprintf(p, left, "\tdevice: %u  lun: %u\n",
>  			     info->params.device_path.atapi.device,
> @@ -545,8 +552,12 @@ edd_has_edd30(struct edd_device *edev)
>  	}
>  
>  
> -	/* We support only T13 spec */
> -	if (info->params.device_path_info_length != 44)
> +	/*
> +	 * Phoenix EDD 3.0 specifies this to be 36,
> +	 * T-13 EDD 3.0 uses 44. So check for both.
> +	 */
> +	if (info->params.device_path_info_length != 36 &&
> +	    info->params.device_path_info_length != 44)
>  		return 0;
>  
>  	for (i = 30; i < info->params.device_path_info_length + 30; i++)

--
			Gleb.
--
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