[PATCH 00/12] xfsprogs: fixup generate_obfuscated_name()

[Alex Elder]

This series has expanded some since I first posted a
version of it back in October.

My original purpose was to fix a bug in the function
used by xfs_metadump to obfuscate file and extended
attribute names.  Arkadiusz Miśkiewicz found out that
when he attempted to perform a metadump on a filesystem
which had some files whose names used 8-bit characters,
it never completed.  The cause was a flaw in the
algorithm used to obfuscate names which caused
an infinite loop when certain names got obfuscated.

I have fixed that bug (in patch 4 of this series), but
while I was at it I rearranged the code a bit and
did some other cleanups.  The first 7 patches in
the series are really pretty directly related to that
issue.

But while in there I noticed some other somewhat
subtle issues and have addressed those in this
series as well:
- There is a table that tracks names to ensure
  duplicates aren't produced as a result of
  obfuscation.  There was a case where a failure
  to update the table was silently ignored.
- There was still a chance that pathological
  cases could end up repeating due to finding
  duplicates.  I changed it so it would give
  up after a fixed number of attempts.
- Obfuscated names had been chosen from an
  alphabet of all allowable characters.  This
  was more than needed, so I made it create
  names that were (mostly) printables.
- It was previously possible for an obfuscated
  name to end up being a duplicate of a real
  name, because non-obfuscated names were not
  placed in the name table.

And finally I did a little tidying of the
code that manages the name table.

Below is a summary of the patches, in order.

					-Alex

xfsprogs: some things aren't all that special
    Some simple code refactoring to make the purpose
    of one help function more focused.
xfsprogs: simplify leading '/' handling in generate_obfuscated_name()
    Another cleanup, to simplify some other changes to come.
xfsprogs: drop unneeded use of a random character
    This tweaks the obfuscated filename algorithm slightly
    to simplify it, while preserving its original properties.
xfsprogs: adjust rather than start over when invalid byte found
    This contains the real fix to the original problem.  This
    patch contains a very long description to explain what's
    happening.  But basically it changes the algorithm so that
    when a bad (random) character is produced, we don't start
    over, but instead modify the character (by flipping a bit),
    resulting in a good character that will be used.
xfsprogs: eliminate a pointless loop in generate_obfuscated_name()
    The previous change made a loop in the code no longer needed.
xfsprogs: Replace repeated blocks with a loop
    The code is now structured so all of the last 5 characters
    in an obfuscated name are handled identically.  This just
    takes advantage of that by using a loop over them.
xfsprogs: use pointers in generate_obfuscated_name()
    Sort of a cleanup, replacing array references with pointers.
xfsprogs: ensure dup table always has entry for obfuscated name
    This just makes sure we create an entry in the name table
    before we pass back an obfuscated name.
xfsprogs: don't loop on too many dups
    This ensures we don't loop forever (or even for very long)
    if we repeatedly come up with duplicate entries when
    obfuscating names.
xfsprogs: use printable characters for obfuscated filenames
    This restricts the characters used for all but the
    last five letters of obfuscated file names to just a
    set of printables.
xfsprogs: fix up the nametable code in db/metadump.c
    This encapsulates some code that works with the
    name table used in tracking duplicates.
xfsprogs: Drop a typedef in db/metadump.c
    This just gets rid of an unnecessary typedef.