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Date: Mon, 22 Apr 2013 17:31:15 +0800
From: Anand Jain <Anand.Jain@oracle.com>
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To: Eric Sandeen <sandeen@redhat.com>
CC: linux-btrfs <linux-btrfs@vger.kernel.org>,
        Alexander Block <ablock84@googlemail.com>
Subject: Re: [PATCH 2/2 V2] btrfs-progs: update generation_v2 in btrfs_update_root
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>   	/*
> -	* If the btrfs-progs is newer and kernel is at
> -	* generation_v1 then we don't touch v2 items
> -	* otherwise when kernel is at same or greater
> -	* version compared with btrfs-progs then update
> -	* the needed
> -	*/
> -	old_size = btrfs_item_size_nr(l, slot);
> -	if (old_size >= sizeof(*item)) {
> -		btrfs_set_root_generation_v2(item,
> -			btrfs_root_generation(item));
> +	 * If this is the first time we update the root item which originated
> +	 * from an older kernel, we need to enlarge the item size to make room
> +	 * for the added fields.
> +	 */
> +	if (old_len < sizeof(*item)) {

  With this fix. when kernel is using v1 and btrfs-progs is
  using v2, the disk structure will be changed to v2 after
  running btrfs check. I would rather take a conservative
  approach, by maintaining kernel intended version.

  Thanks, Anand