A useful VFS change ...

[Jeremy Allison]

On Wed, Feb 26, 2014 at 10:32:13AM -0800, Richard Sharpe wrote:
> On Wed, Feb 26, 2014 at 10:30 AM, Jeremy Allison <jra at samba.org> wrote:
> > On Wed, Feb 26, 2014 at 10:28:37AM -0800, Richard Sharpe wrote:
> >> Hi folks,
> >>
> >> In discussions with Dustin an idea was proposed for a way to make VFS
> >> writing easier for those who are accessing user-space file systems (of
> >> which we are seeing more and more these days.)
> >>
> >> One of the problems is that a user-space file system cannot, in
> >> general, fall through to vfs_defaults, because, except in limited
> >> cases, these call into the kernel via syscalls with FDs that make no
> >> sense to the kernel.
> >>
> >> This requires that the VFS write write code for every VFS function
> >> with many of them simply returning ENOTSUP.
> >>
> >> By adding a set of flags to the structure we could simplify things.
> >> Perhaps we should go back to the old idea of OPAQUE vs TRANSPARENT VFS
> >> modules. The default is TRANSPARENT, but if the writer sets the OPAQUE
> >> bit, the infrastructure will return ENOTSUP if a call is made to a VFS
> >> function that is not implemented.
> >
> > Rather than complicating the structure, shouldn't we
> > just create a new 'defaults' module that always returns
> > ENOTSUP for every call, that OEMs can then stack their
> > user-space filesystem modules on top of ?
> 
> That would do the job as well.

Might be a bit easier, we just copy the skel_opaque.c
module and change the returns..