[Gluster-devel] Implementing Flat Hierarchy for trashed files

[Anoop C S]

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

Proposed Flat hierarchy
=======================
* 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

Other enhancements
==================
* 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