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

[Vivek Goyal <vgoyal@redhat.com>]

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().

Vivek