linux-kernel - Re: [PATCH v2] Btrfs: qgroup: add BUILD

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Date:	Fri, 21 Nov 2014 16:46:17 +0100
From:	David Sterba <dsterba@...e.cz>
To:	Daniel Dressler <danieru.dressler@...il.com>
Cc:	Chris Mason <clm@...com>, Josef Bacik <jbacik@...com>,
	"open list:BTRFS FILE SYSTEM" <linux-btrfs@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] Btrfs: qgroup: add BUILD_BUG to report pointer cast
 breakage

On Thu, Nov 13, 2014 at 12:54:39AM +0900, Daniel Dressler wrote:
> Our ulist data structure stores at max 64bit
> values. qgroup has used this structure to store
> pointers. In the future when we upgrade to 128bit
> this casting of pointers to uint64_t will break.

What are we going to upgrade to 128 bits?

> This patch adds a BUILD_BUG ensuring that this
> code will not be left untouched in the upgrade.
> 
> It also marks this issue on the TODO list so it
> may be addressed before such an upgrade.
> 
> +	(BUILD_BUG_ON_ZERO(sizeof(uintptr_t) > sizeof(u64)) + \

So it's pointers, this is similar to the 32bit -> 64bit transition, a
change that will affect everything, one BUILD_BUG on does not make any
difference.
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