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Date: Fri, 18 Dec 2009 12:39:50 +0800
Message-ID: <9bd6b5360912172039y432361fu243d0f05bf75b7b7@mail.gmail.com>
Subject: Re: [PATCH] btrfs: Simplify offset calculation method for ctree.h
From: sniper <s3c24xx@gmail.com>
To: Zhaolei <zhaolei@cn.fujitsu.com>
Cc: "linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>,
       LKML <linux-kernel@vger.kernel.org>
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No, many pointers in btrfs function arguments are not pointing to an
absolute address, but relative to the start address of extent.

Take following function as example, argument inode_item is an offset
value to the beginning of leaf. So we can't reach its member with
&inode_item->xxx

>  static inline struct btrfs_timespec *
>  btrfs_inode_mtime(struct btrfs_inode_item *inode_item)
>  {
> -       unsigned long ptr = (unsigned long)inode_item;
> -       ptr += offsetof(struct btrfs_inode_item, mtime);
> -       return (struct btrfs_timespec *)ptr;
> +       return &inode_item->mtime;
>  }
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