Re: [PATCH v9 08/15] ovl: Copy up only metadata during copy up where it makes sense

[Vivek Goyal <vgoyal@redhat.com>]

On Tue, Jan 09, 2018 at 11:49:11AM +0100, Miklos Szeredi wrote:
> On Mon, Jan 8, 2018 at 6:03 PM, Vivek Goyal <vgoyal@redhat.com> wrote:
> > On Mon, Jan 08, 2018 at 11:35:09AM +0100, Miklos Szeredi wrote:
> >> On Wed, Nov 29, 2017 at 4:54 PM, Vivek Goyal <vgoyal@redhat.com> wrote:
> >> > If it makes sense to copy up only metadata during copy up, do it. This
> >> > is done for regular files which are not opened for WRITE and have origin
> >> > being saved.
> >> >
> >> > Right now ->metacopy is set to 0 always. Last patch in the series will
> >> > remove the hard coded statement and enable metacopy feature.
> >> >
> >> > Reviewed-by: Amir Goldstein <amir73il@gmail.com>
> >> > Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
> >> > ---
> >> >  fs/overlayfs/copy_up.c | 38 +++++++++++++++++++++++++++++++-------
> >> >  1 file changed, 31 insertions(+), 7 deletions(-)
> >> >
> >> > diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
> >> > index 31711edf5bde..c5804b87f3c7 100644
> >> > --- a/fs/overlayfs/copy_up.c
> >> > +++ b/fs/overlayfs/copy_up.c
> >> > @@ -232,6 +232,26 @@ int ovl_set_attr(struct dentry *upperdentry, struct kstat *stat)
> >> >         return err;
> >> >  }
> >> >
> >> > +static bool ovl_need_meta_copy_up(struct dentry *dentry, umode_t mode,
> >> > +                                 int flags)
> >> > +{
> >> > +       struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
> >> > +
> >> > +       /* TODO: Will enable metacopy in last patch of series */
> >> > +       return false;
> >> > +
> >> > +       if (!ofs->config.metacopy)
> >> > +               return false;
> >> > +
> >> > +       if (!S_ISREG(mode))
> >> > +               return false;
> >> > +
> >> > +       if (flags && ((OPEN_FMODE(flags) & FMODE_WRITE) || (flags & O_TRUNC)))
> >> > +               return false;
> >> > +
> >> > +       return true;
> >> > +}
> >> > +
> >> >  struct ovl_fh *ovl_encode_fh(struct dentry *lower, bool is_upper)
> >> >  {
> >> >         struct ovl_fh *fh;
> >> > @@ -305,11 +325,8 @@ static int ovl_set_origin(struct dentry *dentry, struct dentry *lower,
> >> >                         return PTR_ERR(fh);
> >> >         }
> >> >
> >> > -       /*
> >> > -        * Do not fail when upper doesn't support xattrs.
> >> > -        */
> >> >         err = ovl_check_setxattr(dentry, upper, OVL_XATTR_ORIGIN, fh,
> >> > -                                fh ? fh->len : 0, 0);
> >> > +                                fh ? fh->len : 0, -EOPNOTSUPP);
> >> >         kfree(fh);
> >> >
> >> >         return err;
> >> > @@ -326,6 +343,7 @@ struct ovl_copy_up_ctx {
> >> >         struct qstr destname;
> >> >         struct dentry *workdir;
> >> >         bool tmpfile;
> >> > +       bool metacopy;
> >> >  };
> >> >
> >> >  static int ovl_link_up(struct ovl_copy_up_ctx *c)
> >> > @@ -453,10 +471,14 @@ static int ovl_copy_up_inode(struct ovl_copy_up_ctx *c, struct dentry *temp)
> >> >          *
> >> >          */
> >> >         err = ovl_set_origin(c->dentry, c->lowerpath.dentry, temp);
> >> > -       if (err)
> >> > -               return err;
> >> > +       if (err) {
> >> > +               if (err != -EOPNOTSUPP)
> >> > +                       return err;
> >> > +               /* Upper does not support xattr. Copy up data as well */
> >> > +               c->metacopy = false;
> >>
> >> Isn't this supposed to be checked in ovl_get_super()?
> >
> > Hi Miklos,
> >
> > Right. I think I was confused by code in ovl_check_setxattr().
> >
> > int ovl_check_setxattr(struct dentry *dentry, struct dentry *upperdentry,
> >                        const char *name, const void *value, size_t size,
> >                        int xerr)
> > {
> >         int err;
> >         struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
> >
> >         if (ofs->noxattr)
> >                 return xerr;
> >
> >         err = ovl_do_setxattr(upperdentry, name, value, size, 0);
> >
> >         if (err == -EOPNOTSUPP) {
> >                 pr_warn("overlayfs: cannot set %s xattr on upper\n", name);
> >                 ofs->noxattr = true;
> >                 return xerr;
> >         }
> >
> >         return err;
> > }
> >
> > ofs->noxattr will be set at mount time. Still we check for -EOPNOTSUPP
> > and set ofs->noxattr again. Is there a situation where this can happen.
> > Is it intentional. Can we get rid of this code.
> >
> > To take care of this situation, I put that code. That is at mount time
> > xattr was fine and hence ofs->noxattr=false. But later somehow we
> > encountered -EOPNOTSUPP while doing ovl_set_origin(). Current code
> > does not fail copy up operation and I tried to retain same behavior.
> > That is just disable metacopy in such case but continue.
> >
> > So if we don't expect all this to happen at all, then I can get rid
> > of this -EOPNOTSUPP check both from ovl_check_setxattr() as well
> > as ovl_copy_up_inode().
> 
> It would be really weird to encounter this, so I think possibly a
> WARN_ON(err == -EOPNOTSUPP) is enough to make sure reality matches our
> expectations.

Hi Miklos,

Effectively that's what current code is doing. Only difference is that it
does a pr_warn() instead of WARN_ON().

So that means I leave current code as it is. Or replace pr_warn() with
WARN_ON(). Something like.

if (WARN_ON(err == -EOPNOTSUPP)) {
	ofs->noxattr = true;
	return xerr;
}

And my code in ovl_copy_up_inode() will continue to remain same as it
will need to handle unexpected -EOPNOTSUPP and disable metacopy operation
for that particular copy up.

Vivek