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Subject: Re: [PATCH v2 1/3] fs: add infrastructure for multigrain inode
 i_m/ctime
From:   Jeff Layton <jlayton@kernel.org>
To:     NeilBrown <neilb@suse.de>
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Christian Brauner <brauner@kernel.org>,
        "Darrick J. Wong" <djwong@kernel.org>,
        Hugh Dickins <hughd@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Dave Chinner <david@fromorbit.com>,
        Chuck Lever <chuck.lever@oracle.com>, Jan Kara <jack@suse.cz>,
        Amir Goldstein <amir73il@gmail.com>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-xfs@vger.kernel.org, linux-mm@kvack.org,
        linux-nfs@vger.kernel.org
Date:   Tue, 25 Apr 2023 13:45:19 -0400
In-Reply-To: <168237601955.24821.11999779095797667429@noble.neil.brown.name>
References: <20230424151104.175456-1-jlayton@kernel.org>
        , <20230424151104.175456-2-jlayton@kernel.org>
        , <168237287734.24821.11016713590413362200@noble.neil.brown.name>
        , <404a9a8066b0735c9f355214d4eadf0d975b3188.camel@kernel.org>
         <168237601955.24821.11999779095797667429@noble.neil.brown.name>
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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 t=
he ts
> > > > +	 * granularity.
> > > > +	 */
> > > > +	return (sb->s_flags & SB_MULTIGRAIN_TS) &&
> > > > +		!WARN_ON_ONCE(sb->s_time_gran =3D=3D 1);
> > >=20
> > >  Maybe=20
> > > 		!WARN_ON_ONCE(sb->s_time_gran & SB_MULTIGRAIN_TS);
> > >  ??
> > >=20
> >=20
> > I'm not sure I understand what you mean here.
>=20
> That's fair, as what I wrote didn't make any sense.
> I meant to write:
>=20
>  		!WARN_ON_ONCE(sb->s_time_gran & I_CTIME_QUERIED);
>=20
> 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.=20
>  =20

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.

--=20
Jeff Layton <jlayton@kernel.org>