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Date:   Wed, 3 Jun 2020 09:56:13 +0800
From:   Xiao Yang <>
To:     "Darrick J. Wong" <>
CC:     <>, <>,
        Dan Williams <>,
        Dave Chinner <>,
        Christoph Hellwig <>,
        "Theodore Y. Ts'o" <>, Jan Kara <>,
        Jeff Moyer <>, <>,
        <>, <>
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?
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
> .

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