From mboxrd@z Thu Jan  1 00:00:00 1970
From: Amir Goldstein <amir73il@gmail.com>
Subject: Re: On-disk field assignments for metadata checksum and snapshots
Date: Fri, 16 Sep 2011 15:12:19 +0300
Message-ID: <CAOQ4uxi1W9D0Xe5WWbJVyNWMjoCtmdk4JE_x0mzjDCEO7OFcPg@mail.gmail.com>
References: <E1R4Dby-0005qO-I2@tytso-glaptop.cam.corp.google.com>
	<CAOQ4uxihCk=o2C8Htzn5JgnbZ3zRSS+JhaiCw=gcDdgLojd94Q@mail.gmail.com>
	<20110915175755.GK15782@thunk.org>
	<CAOQ4uxgXzNrrsAiii9iUetiiz-RdK+SixoRiPfGEp7zTPsLCGQ@mail.gmail.com>
	<CAGBYx2ZZzftLcbkTXJY6nYed4eSRhXNC6oPzm7rfLiSt0YGMxQ@mail.gmail.com>
	<CAOQ4uxgprEywkyeqAvQp9Cj=vs4RGDh35dLUyUuWThLdTccFWQ@mail.gmail.com>
	<CAGBYx2Yzb=zt-Bay8iTzkFD6SJu+GW_qgw2+QXD-djnnqdq_uw@mail.gmail.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: QUOTED-PRINTABLE
Cc: "Ted Ts'o" <tytso@mit.edu>, "Darrick J. Wong" <djwong@us.ibm.com>,
	linux-ext4@vger.kernel.org,
	Andreas Dilger <adilger.kernel@dilger.ca>
To: Yongqiang Yang <xiaoqiangnk@gmail.com>
Return-path: <linux-ext4-owner@vger.kernel.org>
Received: from mail-wy0-f180.google.com ([74.125.82.180]:39364 "EHLO
	mail-wy0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1753436Ab1IPMMV convert rfc822-to-8bit (ORCPT
	<rfc822;linux-ext4@vger.kernel.org>); Fri, 16 Sep 2011 08:12:21 -0400
Received: by wyj26 with SMTP id 26so4664802wyj.11
        for <linux-ext4@vger.kernel.org>; Fri, 16 Sep 2011 05:12:20 -0700 (PDT)
In-Reply-To: <CAGBYx2Yzb=zt-Bay8iTzkFD6SJu+GW_qgw2+QXD-djnnqdq_uw@mail.gmail.com>
Sender: linux-ext4-owner@vger.kernel.org
List-ID: <linux-ext4.vger.kernel.org>

On Fri, Sep 16, 2011 at 3:00 PM, Yongqiang Yang <xiaoqiangnk@gmail.com>=
 wrote:
> On Fri, Sep 16, 2011 at 7:48 PM, Amir Goldstein <amir73il@gmail.com> =
wrote:
>> On Fri, Sep 16, 2011 at 2:35 PM, Yongqiang Yang <xiaoqiangnk@gmail.c=
om> wrote:
>>> On Fri, Sep 16, 2011 at 2:52 PM, Amir Goldstein <amir73il@gmail.com=
> wrote:
>>>> On Thu, Sep 15, 2011 at 8:57 PM, Ted Ts'o <tytso@mit.edu> wrote:
>>>>> On Thu, Sep 15, 2011 at 07:01:47PM +0300, Amir Goldstein wrote:
>>>>>> > + =A0 =A0 =A0 { =A0 =A0 =A0 E2P_FEATURE_COMPAT, EXT2_FEATURE_C=
OMPAT_EXCLUDE_BITMAP,
>>>>>> > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 "snapshot" },
>>>>>>
>>>>>> The feature name should read "exclude_bitmap".
>>>>>> This is a COMPAT feature which should be set by default on every=
 mkfs.ext4.
>>>>>> The "has_snapshot" (or "snapshots") feature is a RO_COMPAT featu=
re, which
>>>>>> can be turned on and off, depending on whether you want to enabl=
e or
>>>>>> disable snapshots.
>>>>>
>>>>> Yeah, I was trying to use a name which would be a bit more descri=
ptive
>>>>> than "exclude_bitmap", but I agree that will get very confusing w=
ith
>>>>> the "has_snapshot" feature name.
>>>>>
>>>>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0 =A0 =A0 =A0 =A0 =A0- Ted
>>>>>
>>>>
>>>> maybe we can simply call it snapshot_bitmap, if it pleases everyon=
e ;-)
>>> active_snapshot_bitmap will be clearer.:-)
>>
>> clearer to who?
> To code reviewers, actually bits in exclude bitmap are set only if th=
e
> blocks are used by active/current snapshot inode.
>

=46irst, I was never suggesting to change the name of the feature in th=
e
code, only
the way it is presented by tune2fs -l.
Second, you are confusing exclude_bitmap with cow_bitmap (or
active_snapshot_cow_bitmap).
The bits in exclude_bitmap are set for *ALL* blocks of *ALL* snapshots.
So "snapshot_bitmap" or "snapshots_bitmap" is an appropriate name.

Amir.
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" i=
n
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html