Re: [PATCH] ovl: consistent behavior for immutable/append-only inodes

[Miklos Szeredi <miklos@szeredi.hu>]

On Wed, 9 Jun 2021 at 08:08, Amir Goldstein <amir73il@gmail.com> wrote:
>
> On Tue, Jun 8, 2021 at 9:20 PM Miklos Szeredi <miklos@szeredi.hu> wrote:
> >
> > On Tue, 8 Jun 2021 at 17:33, Amir Goldstein <amir73il@gmail.com> wrote:
> > >
> > > On Tue, Jun 8, 2021 at 5:49 PM Miklos Szeredi <miklos@szeredi.hu> wrote:
> > > >
> > > > On Tue, 8 Jun 2021 at 16:37, Amir Goldstein <amir73il@gmail.com> wrote:

> > > > > While you are here, do you think that will be sufficient for the on-disk format
> > > > > of overlay.xflags?
> > > > >
> > > > > struct ovl_xflags {
> > > > >         __le32 xflags;
> > > > >         __le32 xflags_mask;
> > > > > }
> > > >
> > > > I think I'd prefer a slightly more complex, but user friendlier
> > > > "+i,-a,..." format.
> > > >
> > >
> > > OK, but since this is not a merge, we'd only need:
> > > overlay.xflags = "ia..."
> > >
> > > Which is compatible with the format of:
> > > chattr =<xflags> <file>
> >
> > Fine.   Not sure what xflags_mask would be useful for in your proposal, though.
> >
>
> The idea was that in the context of fileattr_get(), any specific xflag
> value can be one of: SET, CLEAR, REAL.
>
> For most inodes all flags are REAL (no xflags xattr)
> All flags but the 4 in OVL_FS_XFLAGS_MASK are always REAL
> (i.e. taken from fileattr_get() on real inode).
>
> If we ever decide to extend OVL_FS_XFLAGS_MASK, say to include
> DIRSYNC, then an upper inode with DIRSYNC that was in state
> REAL before upgrade would become CLEAR after upgrade unless
> we kept the old xflags_mask in xattr.
>
> With the string format, this is not a concern.
> Therefore, I like the string format better.

Hmm, so if the attribute letters would have fixed places in the string
and clear attributes would be represented by a space or a "-" then
that would be similarly extensible.   Just having a list of set
attribute letters would not allow having three states.

Thanks,
Miklos