Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20210923130814.140814-1-cgxu519@mykernel.net> <20210923130814.140814-7-cgxu519@mykernel.net>
 <CAJfpeguqj2vst4Zj5EovSktJkXiDSCSWY=X12X0Yrz4M8gPRmQ@mail.gmail.com> <17c5aba1fef.c5c03d5825886.6577730832510234905@mykernel.net>
In-Reply-To: <17c5aba1fef.c5c03d5825886.6577730832510234905@mykernel.net>
From:   Miklos Szeredi <miklos@szeredi.hu>
Date:   Thu, 7 Oct 2021 14:45:20 +0200
Message-ID: <CAJfpegtr1NkOiY9YWd1meU1yiD-LFX-aB55UVJs94FrX0VNEJQ@mail.gmail.com>
Subject: Re: [RFC PATCH v5 06/10] ovl: implement overlayfs' ->write_inode operation
To:     Chengguang Xu <cgxu519@mykernel.net>
Cc:     Jan Kara <jack@suse.cz>, Amir Goldstein <amir73il@gmail.com>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        overlayfs <linux-unionfs@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Thu, 7 Oct 2021 at 14:28, Chengguang Xu <cgxu519@mykernel.net> wrote:
>
>  ---- =E5=9C=A8 =E6=98=9F=E6=9C=9F=E5=9B=9B, 2021-10-07 17:23:06 Miklos S=
zeredi <miklos@szeredi.hu> =E6=92=B0=E5=86=99 ----
>  > On Thu, 23 Sept 2021 at 15:08, Chengguang Xu <cgxu519@mykernel.net> wr=
ote:
>  > >
>  > > Implement overlayfs' ->write_inode to sync dirty data
>  > > and redirty overlayfs' inode if necessary.
>  > >
>  > > Signed-off-by: Chengguang Xu <cgxu519@mykernel.net>
>  > > ---
>  > >  fs/overlayfs/super.c | 30 ++++++++++++++++++++++++++++++
>  > >  1 file changed, 30 insertions(+)
>  > >
>  > > diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
>  > > index 2ab77adf7256..cddae3ca2fa5 100644
>  > > --- a/fs/overlayfs/super.c
>  > > +++ b/fs/overlayfs/super.c
>  > > @@ -412,12 +412,42 @@ static void ovl_evict_inode(struct inode *inod=
e)
>  > >         clear_inode(inode);
>  > >  }
>  > >
>  > > +static int ovl_write_inode(struct inode *inode,
>  > > +                          struct writeback_control *wbc)
>  > > +{
>  > > +       struct ovl_fs *ofs =3D inode->i_sb->s_fs_info;
>  > > +       struct inode *upper =3D ovl_inode_upper(inode);
>  > > +       unsigned long iflag =3D 0;
>  > > +       int ret =3D 0;
>  > > +
>  > > +       if (!upper)
>  > > +               return 0;
>  > > +
>  > > +       if (!ovl_should_sync(ofs))
>  > > +               return 0;
>  > > +
>  > > +       if (upper->i_sb->s_op->write_inode)
>  > > +               ret =3D upper->i_sb->s_op->write_inode(inode, wbc);
>  >
>  > Where is page writeback on upper inode triggered?
>  >
>
> Should pass upper inode instead of overlay inode here.

That's true and it does seem to indicate lack of thorough testing.

However that wasn't what I was asking about.  AFAICS ->write_inode()
won't start write back for dirty pages.   Maybe I'm missing something,
but there it looks as if nothing will actually trigger writeback for
dirty pages in upper inode.

Thanks,
Miklos