linux-kernel - Re: Re: [PATCH] btrfs: Simplify offset calculation method for ctree.h

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Date:	Fri, 18 Dec 2009 13:51:14 +0800
From:	Zhaolei <zhaolei@...fujitsu.com>
To:	sniper <s3c24xx@...il.com>
CC:	"linux-btrfs@...r.kernel.org" <linux-btrfs@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Re: [PATCH] btrfs: Simplify offset calculation method for ctree.h

sniper wrote:
> 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

Notice that we are not reach its member, we are getting pointer of its
member with &inode_item->mtime.
This operation have same effect as old one.

Thanks
Zhaolei

> 
>>  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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