Re: [PATCH 5/7] ovl: Set OVL_METACOPY flag during ovl_lookup()

[Vivek Goyal <vgoyal@redhat.com>]

On Mon, Oct 02, 2017 at 10:31:42PM +0300, Amir Goldstein wrote:
> On Mon, Oct 2, 2017 at 4:40 PM, Vivek Goyal <vgoyal@redhat.com> wrote:
> > During lookup, check for presence of OVL_XATTR_METACOPY and if present,
> > set OVL_METACOPY bit in flags.
> >
> > Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
> > ---
> >  fs/overlayfs/namei.c | 34 ++++++++++++++++++++++++++++++++++
> >  1 file changed, 34 insertions(+)
> >
> > diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
> > index c3addd1114f1..9b6f9afa4f75 100644
> > --- a/fs/overlayfs/namei.c
> > +++ b/fs/overlayfs/namei.c
> > @@ -26,6 +26,24 @@ struct ovl_lookup_data {
> >         char *redirect;
> >  };
> >
> > +/* err < 0, 0 if no metacopy xattr, 1 if metacopy xattr found */
> > +static int ovl_check_metacopy(struct dentry *dentry)
> > +{
> > +       int res;
> > +
> > +       res = vfs_getxattr(dentry, OVL_XATTR_METACOPY, NULL, 0);
> > +       if (res < 0) {
> > +               if (res == -ENODATA || res == -EOPNOTSUPP)
> > +                       return 0;
> > +               goto out;
> > +       }
> > +
> > +       return 1;
> > +out:
> > +       pr_warn_ratelimited("overlayfs: failed to get metacopy (%i)\n", res);
> > +       return res;
> > +}
> > +
> >  static int ovl_check_redirect(struct dentry *dentry, struct ovl_lookup_data *d,
> >                               size_t prelen, const char *post)
> >  {
> > @@ -591,6 +609,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> >         struct dentry *this;
> >         unsigned int i;
> >         int err;
> > +       bool metacopy = false;
> >         struct ovl_lookup_data d = {
> >                 .name = dentry->d_name,
> >                 .is_dir = false,
> > @@ -631,6 +650,12 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> >                                                roe->numlower, &stack, &ctr);
> >                         if (err)
> >                                 goto out;
> > +
> > +                       err = ovl_check_metacopy(upperdentry);
> > +                       if (err < 0)
> > +                               goto out;
> > +                       if (err == 1)
> > +                               metacopy = true;
> >                 }
> >
> >                 if (d.redirect) {
> > @@ -716,6 +741,15 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> >                 OVL_I(inode)->redirect = upperredirect;
> >                 if (index)
> >                         ovl_set_flag(OVL_INDEX, inode);
> > +
> > +               if (metacopy) {
> > +                       /*
> > +                        * TODO: What happens we if find metacopy xattr but
> > +                        * could not find/resolve origin.
> > +                        */
> 
> Hint: if metacopy could also exist only on an index entry, with no
> upper aliases,
> this index entry would be detected as stale on mount (cannot resolve origin) and
> cleaned, so you won't get to this problem.

Hi Amir,

Sorry, I am getting lost here. Can you please explain a bit more.

My understanding is that index entry is created during copy up only for
files with nlink > 1. If a regular file is copied up there will not be
any index entry.

And during mount time, you are going through all index entries and
verifying there are no stale entries and cleaning up stale entries.
(ovl_indexdir_cleanup()).

So is the idea that with metacopyup we create index entries even for
regular files with nlink=1 and do similar cleanup? Sorry, I am little
lost here.

Vivek