Make VFS op "streaminfo" stackable

[Jeremy Allison]

On Fri, Aug 26, 2011 at 06:33:13PM +0200, Frank Lahm wrote:
> Hi,
> 
> thanks for providing feedback!
> 
> 2011/8/26 Volker Lendecke <Volker.Lendecke at sernet.de>:
> > On Fri, Aug 26, 2011 at 03:53:12PM +0200, Frank Lahm wrote:
> >> 2011/8/26 Frank Lahm <franklahm at googlemail.com>:
> >> > I'm currently starring at struct vfs_handle_struct trying to come up
> >> > with anything that could be used to determine inside
> >> > smb_vfs_call_streaminfo() whether it has been called through
> >> > SMB_VFS_STREAMINFO (which should do the initialisation) or
> >> > SMB_VFS_NEXT_STREAMINFO.
> >>
> >> This should work, shouldn't it ?
> >>
> >>
> >> diff --git a/source3/smbd/vfs.c b/source3/smbd/vfs.c
> >> index 35a8331..c846174 100644
> >> --- a/source3/smbd/vfs.c
> >> +++ b/source3/smbd/vfs.c
> >> @@ -1673,6 +1673,11 @@ NTSTATUS smb_vfs_call_streaminfo(struct
> >> vfs_handle_struct *handle,
> >>                                  struct stream_struct **streams)
> >>  {
> >>         VFS_FIND(streaminfo);
> >> +       if (handle->prev->next == NULL) {
> >> +               /* VFS op chain start */
> >> +               *num_streams = 0;
> >> +               *streams = NULL;
> >> +       }
> >>         return handle->fns->streaminfo(handle, fsp, fname, mem_ctx,
> >>                                        num_streams, streams);
> >>  }
> >
> > It might work, but I think this is the wrong layer. The
> > semantics of the streaminfo call would be that every module
> > adds its streams, otherwise you don't get stackability.
> 
> Yes, but imo this doesn't make an argument where the initialisation
> has to be done: by the caller or by the callee. Following my approach
> has the benefit that the caller mustn't remember to do any special
> initialisation with streaminfo compared to other VFS ops (if any) that
> return results via function parameters.

To do special initialization before calling a vfs op, use a wrapper
function and then ensure all calls from the main code go through
this. See functions like vfs_stat_fsp() for details.

Jeremy.