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Date:   Thu, 2 Apr 2020 13:55:19 -0700
From:   Ira Weiny <>
To:     Christoph Hellwig <>
Cc:     Jan Kara <>,
        "Darrick J. Wong" <>,
        Dave Chinner <>,
        "Theodore Y. Ts'o" <>,
        Dan Williams <>,
        Linux Kernel Mailing List <>,
        Alexander Viro <>,
        linux-ext4 <>,
        linux-xfs <>,
        linux-fsdevel <>,
        Andrew Morton <>,
        Linus Torvalds <>
Subject: Re: [PATCH V5 00/12] Enable per-file/per-directory DAX operations V5

On Thu, Apr 02, 2020 at 10:53:27AM +0200, Christoph Hellwig wrote:
> On Wed, Apr 01, 2020 at 12:25:11PM +0200, Jan Kara wrote:
> > >  - Applications must call statx to discover the current S_DAX state.
> > > 
> > >  - There exists an advisory file inode flag FS_XFLAG_DAX that can be
> > >    changed on files that have no blocks allocated to them.  Changing
> > >    this flag does not necessarily change the S_DAX state immediately
> > >    but programs can query the S_DAX state via statx.
> > 
> > I generally like the proposal but I think the fact that toggling
> > FS_XFLAG_DAX will not have immediate effect on S_DAX will cause quite some
> > confusion and ultimately bug reports. I'm thinking whether we could somehow
> > improve this... For example an ioctl that would try to make set inode flags
> > effective by evicting the inode (and returning EBUSY if the eviction is
> > impossible for some reason)?
> I'd just return an error for that case, don't play silly games like
> evicting the inode.

I think I agree with Christoph here.  But I want to clarify.  I was heading in
a direction of failing the ioctl completely.  But we could have the flag change
with an appropriate error which could let the user know the change has been

But I don't immediately see what error code is appropriate for such an
indication.  Candidates I can envision:


None are perfect but I'm leaning toward EINPROGRESS.


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