[Gluster-devel] Implementing Flat Hierarchy for trashed files

[Niels de Vos]

On Mon, Aug 17, 2015 at 06:20:50PM +0530, Anoop C S wrote:
> Hi all,
> 
> As we move forward, in order to fix the limitations with current trash
> translator we are planning to replace the existing criteria for trashed
> files inside trash directory with a general flat hierarchy as described
> in the following sections. Please have your thoughts on following
> design considerations.
> 
> Current implementation
> ======================
> * Trash translator resides on glusterfs server stack just above posix.
> * Trash directory (.trashcan) is created during volume start and is
>   visible under root of the volume.
> * Each trashed file is moved (renamed) to trash directory with an
>   appended time stamp in the file name. 
> * Exact directory hierarchy (w.r.t the root of volume) is maintained
>   inside trash directory whenever a file is deleted/truncated from a
>   directory
> 
> Outstanding issues
> ==================
> * Since renaming occurs at the server side, client-side is unaware of
>   trash doing rename or create operations.
> * As a result files/directories may not be visible from mount point.

This might be something upcall could help with. If the trash xlator is
placed above upcall, any clients interested in the .trashcan directory
(or subdirs) could get an in/revalidation request.

> * Files/Directories created from from trash translator will not have
>   gfid associated with it until lookup is performed.

When a client receives an invalidation of the parent directory (from
upcall), a LOOKUP will follow on the next request.

> Proposed Flat hierarchy
> =======================

I'm missing a bit of info here, what limitations need to be addressed?

> * Instead of creating the whole directory under trash, we will rename
>   the file and place it directly under trash directory (of course with
>   appended time stamp).
> * Directory hierarchy can be stored via either of the following two
>   approaches:
> 	(a) File name will contain the whole path with time stamp
> 	    appended
> 	(b) Store whole hierarchy as an xattr

If this is needed, definitely go with (b). Filenames have a limit, and
the full path (directories + filename + timestamp) could surely hit
that.

> Other enhancements
> ==================

Have these been filed as bugs/RFEs? If not, please do so and include a
good description of the work that is needed. Maybe others in the Gluster
community are interested in providing patches, and details on what to do
is very helpful.

Thanks,
Niels

> * Create the trash directory only
> when trash xlator is enabled.
> * Operations such as unlink, rename etc
> will be prevented on trash
>   directory only when trash xlator is
> enabled.
> * A new trash helper translator on client side(loaded only when
> trash
>   is enabled) to resolve split brain issues with truncation of
> files.
> * Restore files from trash with the help of an explicit setfattr
> call.
> 
> Thanks & Regards,
> -Anoop C S
> -Jiffin Tony Thottan
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