Make VFS op "streaminfo" stackable

[Frank Lahm]

Hi,

2011/8/26, Jeremy Allison <jra at samba.org>:
> 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.

ok.

Thanks!
-f