linux-kernel - Re: [PATCH] Btrfs: qgroup: add BUILD_BUG to report pointer cast breakage

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Date:	Thu, 13 Nov 2014 00:02:14 +0900
From:	Daniel Dressler <danieru.dressler@...il.com>
To:	"danieru.dressler@...il.com" <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] Btrfs: qgroup: add BUILD_BUG to report pointer cast breakage

I am very very sorry, I forgot to even test building. Please pretend
this patch was never submitted.

Daniel

2014-11-13 0:00 GMT+09:00 Daniel Dressler <danieru.dressler@...il.com>:
> 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.
>
> 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.
>
> Signed-off-by: Daniel Dressler <danieru.dressler@...il.com>
> ---
>  fs/btrfs/qgroup.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
> index 48b60db..87f7c98 100644
> --- a/fs/btrfs/qgroup.c
> +++ b/fs/btrfs/qgroup.c
> @@ -44,6 +44,7 @@
>   *  - caches fuer ulists
>   *  - performance benchmarks
>   *  - check all ioctl parameters
> + *  - do not cast uintptr_t to uint64_t in ulist usage
>   */
>
>  /*
> @@ -101,6 +102,7 @@ struct btrfs_qgroup_list {
>
>  #define ptr_to_u64(x) ((u64)(uintptr_t)x)
>  #define u64_to_ptr(x) ((struct btrfs_qgroup *)(uintptr_t)x)
> +BUILD_BUG_ON(UINTPTR_MAX > UINT64_MAX);
>
>  static int
>  qgroup_rescan_init(struct btrfs_fs_info *fs_info, u64 progress_objectid,
> --
> 2.1.0
>
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