Bugzilla Bug 171205

Flexbackup uses either the buffer or mbuffer program to help streaming tape
drives from thrashing.  The buffer program uses the -p command line option to
specify the percentage the buffer to fill before writing data.  Alas, mbuffer's
command line is insidiously incompatible with buffer in this: it uses -P
(capital P) instead of -p (lowercase p) to mean the same thing.  In mbuffer -p
(lowercase p) is for read buffer starvation control as opposed to write buffer
fill control.  Since flexbackup uses -p for both buffer and mbuffer, flexbackup
causes a lot of tape drive thrashing when mbuffer is used, since the write
buffer fill control is not specified.  I've included a patch that corrects this
issue.

In addition, the "find" command line that is constructed to identify files to
backup is awfully complex.  In figuring out how to properly specify directories
to prune, I made a small change to the program itself to log the pruning regex
and added some informative comments to the "flexbackup.conf" file.  The patch
also applies both of these small changes.

Finally, the patch corrects example global exclusions in the "flexbackup.conf"
which actually break a backup under Gentoo because they exclude the backup of
critical Portage components ("/usr/lib/portage/pym/cache", in fact).  Probably
not the best example for a Portage ebuild to install.

The patches are against "flexbackup-1.2.1-r2".  Note that there's a little bit
of correction work on inconsistent indenting in there, too.  I'm going to
submit these patches upstream as well, but, upstream hasn't made any updates
since 2003, so I really think the best way to get 'em into the tree is through
a Gentoo bug.

Reproducible: Always

Steps to Reproduce:
1. Include "$buffer = 'mbuffer';" in "flexbackup.conf".
2. Backup to tape.
Actual Results:  
Tape drive will thrash incessantly during backup:  write a little bit, stop,
backup, repeat.

Expected Results:  
Reasonable buffering should keep tape drive moving in one direction most of the
time.

Created an attachment (id=113532) [edit]
Patch to apply the described fixes.

Created an attachment (id=115060) [edit]
Update the documentation to describe the new features.

Update the documentation (both man page and internal --help documentation) to
describe the new features.

Alas, I also made a small additional code change:  I added a --no-symlink
option as a complimentary option to the new --symlink one.  This allows the
option to be defaulted to on in genkernel.conf and then turned off from the
command line.

(From update of attachment 115060 [edit])
Posted a patch for my genkernel enhancement to the wrong bug.  Sorry for the
trouble.  Please ignore this patch.

Created an attachment (id=116268) [edit]
New patch applies against flexbackup-1.2.1-r3 without annoying offset messages.

This fix is in Portage now as flexbackup-1.2.1-r4 thanks to the help of the
Gentoo Sunrise team.