Re: RFE: per-subvolume timestamp that is updated on every change to a subvolume

[Qu Wenruo <quwenruo@cn.fujitsu.com>]

-------- Original Message --------
Subject: Re: RFE: per-subvolume timestamp that is updated on every 
change to a subvolume
From: Qu Wenruo <quwenruo@cn.fujitsu.com>
To: Lennart Poettering <lennart@poettering.net>, 
<linux-btrfs@vger.kernel.org>
Date: 2015年01月06日 14:02
>
> -------- Original Message --------
> Subject: RFE: per-subvolume timestamp that is updated on every change 
> to a subvolume
> From: Lennart Poettering <lennart@poettering.net>
> To: <linux-btrfs@vger.kernel.org>
> Date: 2015年01月06日 01:27
>> Heya!
>>
>> I am looking for a nice way to query the overall last modification
>> timestamp of a subvolume. i.e. the most recent mtime of *any* file or
>> directory within a subvolume. Ideally, I think, there was a
>> btrfs_timespec field for this in "struct btrfs_root_item", alas there
>> isn't afaics. Any chance this can be added?
> In fact, btrfs_root_item contains one btrfs_inode_item, which contains 
> the a/c/m/otime.
> But not sure if it contains the time you need.
>
> I'd better add acmotime output for inode_item in btrfs-debug-tree and 
> try myself.
>
> Thanks,
> Qu
The value in acmotime of the inode_item in root_item is not used,
so it seems anyone can use it to record the acmotime for your purpose.

Thanks,
Qu
>>
>> Or is there another workable way to query this value? Maybe determine
>> it from the current generation of a subvolume or so? Is that tracked?
>> Ideas?
>>
>> Lennart
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