linux-kernel - Re: [PATCH v2 1/3] fs: add infrastructure for multigrain inode i

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Date:   Tue, 25 Apr 2023 13:45:19 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     NeilBrown <neilb@...e.de>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        "Darrick J. Wong" <djwong@...nel.org>,
        Hugh Dickins <hughd@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Chinner <david@...morbit.com>,
        Chuck Lever <chuck.lever@...cle.com>, Jan Kara <jack@...e.cz>,
        Amir Goldstein <amir73il@...il.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-mm@...ck.org,
        linux-nfs@...r.kernel.org
Subject: Re: [PATCH v2 1/3] fs: add infrastructure for multigrain inode
 i_m/ctime

On Tue, 2023-04-25 at 08:40 +1000, NeilBrown wrote:
> On Tue, 25 Apr 2023, Jeff Layton wrote:
> > On Tue, 2023-04-25 at 07:47 +1000, NeilBrown wrote:
> > > On Tue, 25 Apr 2023, Jeff Layton wrote:
> > > > +	/*
> > > > +	 * Warn if someone sets SB_MULTIGRAIN_TS, but doesn't turn down the ts
> > > > +	 * granularity.
> > > > +	 */
> > > > +	return (sb->s_flags & SB_MULTIGRAIN_TS) &&
> > > > +		!WARN_ON_ONCE(sb->s_time_gran == 1);
> > > 
> > >  Maybe 
> > > 		!WARN_ON_ONCE(sb->s_time_gran & SB_MULTIGRAIN_TS);
> > >  ??
> > > 
> > 
> > I'm not sure I understand what you mean here.
> 
> That's fair, as what I wrote didn't make any sense.
> I meant to write:
> 
>  		!WARN_ON_ONCE(sb->s_time_gran & I_CTIME_QUERIED);
> 
> to make it explicit that s_time_gran must leave space for
> I_CTIME_QUERIED to be set (as you write below).  Specifically that
> s_time_gran mustn't be odd. 
>   

Erm...it may be an unpopular opinion, but I find that more confusing
than just ensuring that the s_time_gran > 1. I keep wondering if we
might want to carve out other low-order bits too for some later purpose,
at which point trying to check this using flags wouldn't work right. I
think I might just stick with what I have here, at least for now.

-- 
Jeff Layton <jlayton@...nel.org>