rsync - Apr 2010 - DO NOT REPLY [Bug 7321] New: Extend "p" filter modifier to make source dirs prunable

https://bugzilla.samba.org/show_bug.cgi?id=7321

           Summary: Extend "p" filter modifier to make source dirs
prunable
           Product: rsync
           Version: 3.1.0
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P3
         Component: core
        AssignedTo: wayned at samba.org
        ReportedBy: matt at mattmccutchen.net
         QAContact: rsync-qa at samba.org


It would be very useful to have a way to traverse source dirs but only add them
to the file list if a descendant is added to the file list.  --prune-empty-dirs
can do this, but it has two significant disadvantages:

- File-list entries are sent to the receiver even if they will later be pruned.
 This wastes bandwidth and unnecessarily leaks potentially private data.

- The single set of receiver-side filters is used for two unrelated tasks:
protecting destination dirs from deletion and protecting source dirs from
pruning.  It should be possible to specify two independent sets of filters. 
This came up once on the list:

http://lists.samba.org/archive/rsync/2008-February/020084.html

So I'd like to propose a new implementation of source pruning. 
(--prune-empty-dirs would remain for compatibility, but the man page would
encourage users to move to the new implementation.)  The "p" filter
modifier,
currently used to mark protect filters perishable, would gain a second meaning
to mark "show" filters prunable.  The analogue to the time-honored
"--include='*/' --exclude='*' --prune-empty-dirs"
combination would be
"--filter='+p */' --exclude='*'" .


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https://bugzilla.samba.org/show_bug.cgi?id=7321





------- Comment #1 from matt at mattmccutchen.net  2010-04-02 17:56 CST -------
This is a new incarnation of my proposal a while ago for a "traverse"
sender
filter action:

http://lists.samba.org/archive/rsync/2005-December/014166.html

Some things I neglected to mention:

- On second thought, overloading the "p" modifier is probably a bad
idea
because it becomes complicated to ensure that a client receiver will fail if
the sender is too old to understand the new semantics.  What would be another
appropriate letter for the prunable modifier?  "m", after
--prune-empty-dirs,
would conflict with my filter-attrs patch (bug 6197).

- At first, the prunable modifier would not work with incremental recursion. 
(That could be improved later as a separate enhancement.)  If a prunable filter
is found during parse_arguments, incremental recursion would simply be
disabled.  Otherwise, we count on the user to pass --no-i-r.  If a run with
incremental recursion is already underway and a prunable filter is found in a
per-dir merge file, rsync would ignore the modifier with an FERROR_XFER.


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