scrub-custom.txt

Based on 'Scrub limited to a subvolume', extended interface to scub any set of files
====================================================================================

REF: scrub-subvolume.txt for intro

Usecase: do a reliable scrub run on a subset of the filesystem, specified by the
user, as a "scrub transaction"

The scrub control interface is defined by:

* start transaction
* add files, directories, subvoulmes
* flush (adding more still posssible)
* end transaction


Start transaction
-----------------

Initialize the internal state and start accepting "add files" commands.


Add files
---------

Use an ioctl to add files to the scrubbed set. Here the 'file' can be a
drectory which will recursively add the whole directory hierarchy (applies to
subvolume as well).

At this point do not do any scanning, just queue a list of requests in memory.


Flush
-----

Process all the queued requests. Scan file extents, build the ranges of chunks
and then scrub the ranges.


End
---

Stop accepting new file additions, flush eventually, finish the scrub
transaction.