linux-ext4 - Re: [PATCH] xfs/XXX: Add xfs/XXX

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Date:   Wed, 3 Jun 2020 09:56:13 +0800
From:   Xiao Yang <yangx.jy@...fujitsu.com>
To:     "Darrick J. Wong" <darrick.wong@...cle.com>
CC:     <ira.weiny@...el.com>, <fstests@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Christoph Hellwig <hch@....de>,
        "Theodore Y. Ts'o" <tytso@....edu>, Jan Kara <jack@...e.cz>,
        Jeff Moyer <jmoyer@...hat.com>, <linux-ext4@...r.kernel.org>,
        <linux-xfs@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH] xfs/XXX: Add xfs/XXX

On 2020/6/3 2:14, Darrick J. Wong wrote:
> On Tue, Jun 02, 2020 at 04:51:48PM +0800, Xiao Yang wrote:
>> On 2020/4/14 0:30, Darrick J. Wong wrote:
>>> This might be a good time to introduce a few new helpers:
>>>
>>> _require_scratch_dax ("Does $SCRATCH_DEV support DAX?")
>>> _require_scratch_dax_mountopt ("Does the fs support the DAX mount options?")
>>> _require_scratch_daX_iflag ("Does the fs support FS_XFLAG_DAX?")
>> Hi Darrick,
>>
>> Now, I am trying to introduce these new helpers and have some questions:
>> 1) There are five testcases related to old dax implementation, should we
>> only convert them to new dax implementation or make them compatible with old
>> and new dax implementation?
>
> What is the 'old' DAX implementation?  ext2 XIP?
Hi Darrick,

Thanks for your quick feedback.

Right, the 'old' DAX implementation means old dax mount option(i.e. -o dax)

Compare new and old dax mount option on ext4 and xfs, is the following 
logic right?
-o dax=always == -o dax
-o dax=never == without dax
-o dax=inode == nothing

Of course, we should uses new option if ext4/xfs supports new dax mount 
option on distros.  But should we fallback to use old option if ext4/xfs 
doesn't support new dax mount option on some old distros?
btw:
it seems hard for testcases to use two different sets of mount 
options(i.e. old and new) so do you have any suggestion?

>
>> 2) I think _require_xfs_io_command "chattr" "x" is enough to check if fs
>> supports FS_XFLAG_DAX.  Is it necessary to add _require_scratch_dax_iflag()?
>> like this:
>> _require_scratch_dax_iflag()
>> {
>> 	_require_xfs_io_command "chattr" "x"
>> }
>
> I suggested that list based on the major control knobs that will be
> visible to userspace programs.  Even if this is just a one-line helper,
> its name is useful for recognizing which of those knobs we're looking
> for.
>
> Yes, you could probably save a trivial amount of time by skipping one
> iteration of bash function calling, but now everyone has to remember
> that the xfs_io chattr "x" flag means the dax inode flag, and not
> confuse it for chmod +x or something else.

Got it, thanks for your detailed explanation.

Best Regards,
Xiao Yang
>
> --D
>
>> Best Regards,
>> Xiao Yang
>>
>>
>
>
> .
>