linux-kernel - Re: [PATCH v2] fix sign extension with 1.5TB usb-storage LBD=y

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Date:	Tue, 21 Apr 2009 17:03:09 -0600
From:	Matthew Wilcox <matthew@....cx>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	mdharm-usb@...-eyed-alien.net,
	linux-usb <linux-usb@...r.kernel.org>,
	usb-storage@...ts.one-eyed-alien.net,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH v2] fix sign extension with 1.5TB usb-storage LBD=y

On Tue, Apr 21, 2009 at 03:00:10PM -0700, Dave Hansen wrote:
> Here's a patch implementing Al's suggestion.  Not quite as trivial as
> Matthew's, but even nicer aesthetically.  (Description stolen from
> Matthew's patch).  I have verified that this fixes my issue.

I prefer this approach, but I'm equally happy with whichever patch
James chooses.

> Shifting an unsigned char implicitly casts it to a signed int.  This
> caused 'lba' to sign-extend and Linux would then try READ CAPACITY 16
> which was not supported by at least one drive.  Using the
> get_unaligned_be*() helpers keeps us from having to worry about how the
> extension might occur.
> 
> Signed-off-by: Dave Hansen <dave@...ux.vnet.ibm.com>

Reviewed-by: Matthew Wilcox <willy@...ux.intel.com>

> @@ -1344,12 +1345,8 @@ static int read_capacity_16(struct scsi_disk *sdkp, struct scsi_device *sdp,
>  		return -EINVAL;
>  	}
>  
> -	sector_size =	(buffer[8] << 24) | (buffer[9] << 16) |
> -			(buffer[10] << 8) | buffer[11];
> -	lba =  (((u64)buffer[0] << 56) | ((u64)buffer[1] << 48) |
> -		((u64)buffer[2] << 40) | ((u64)buffer[3] << 32) |
> -		((u64)buffer[4] << 24) | ((u64)buffer[5] << 16) |
> -		((u64)buffer[6] << 8) | (u64)buffer[7]);
> +	sector_size = get_unaligned_be32(&buffer[8]);
> +	lba =  get_unaligned_be64(&buffer[0]);

The smallest of quibbles ... you have an excess space after the = ...

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."
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