Add support for "bup index --exclude-rx <pattern> ...".

When --exclude-rx <pattern> is provided to bup index, exclude any path
matching <pattern>, which must be a Python regular expression
(http://docs.python.org/library/re.html).  The pattern will be
compared against the full path, without anchoring, so "x/y" will match
"ox/yard" or "box/yards".  To exclude the contents of /tmp, but not
the directory itself, use "^/tmp/.".

You may check the behavior at runtime by setting BUP_DEBUG=2 in the
environment.

Thanks to Zoran Zaric <zz@zoranzaric.de> for reporting a bug in an
earlier version of this patch.

Signed-off-by: Rob Browning <rlb@defaultvalue.org>
Add support for "bup restore --exclude-rx <pattern> ...".

When --exclude-rx <pattern> is provided to bup restore, don't restore
any path matching <pattern>, which must be a Python regular expression
(http://docs.python.org/library/re.html).  The pattern will be
compared against the full path, without anchoring, so "x/y" will match
"ox/yard" or "box/yards".  To exclude the contents of /tmp, but not
the directory itself, use "^/tmp/.".

You may check the behavior at runtime by setting BUP_DEBUG=2 in the
environment.

Signed-off-by: Rob Browning <rlb@defaultvalue.org>
Overhaul restore destination handling, and stripping/grafting behavior.

Change restore to respond to source paths like this (assume outdir
corresponds to "." if there no -C argument or to -C outdir):

  /foo/what/ever - extract ever to outdir/ever
  /foo/what/ever/ - extract ever/* to outdir/*
  /foo/what/ever/. - extract ever/. to outdir/. (i.e. outdir == ever).

Also fix handling of top-level commit symlinks.  Previously bup would
just restore /foo/latest as a dummy symlink like this:

   latest -> ../.commit/SHA

Instead, dereference latest and restore the target instead.

Tighten up stripping/grafting with additional argument checks, and
handle any root collisions by creating a fake root dir (see comments
in save-cmd.py).  Bup still doesn't handle other path collisions yet,
i.e. if both /foo/bar and /bar are remapped to /bar.

Signed-off-by: Rob Browning <rlb@defaultvalue.org>
Cache all password (pwd) and group (grp) database lookups.

Thanks to Jann Horn <jannhorn@googlemail.com> for determining that
even just caching user names and group names could provide a notable
performance improvement in some cases.

Signed-off-by: Rob Browning <rlb@defaultvalue.org>
Handle nonexistent groups in Metadata._apply_common_rec().

Thanks to Oei, Yung-Chin <yungchin@yungchin.nl> for tracking this
down.

Reported-by: Yung-Chin <yungchin@yungchin.nl>
Signed-off-by: Rob Browning <rlb@defaultvalue.org>
Change index; include atime; pack time as xstat timespec; use ns in memory.

Update the index format header to 'BUPI\0\0\0\4' (version 4).

Change the index to include atimes, and write all times to bupindex as
xstat timespecs.  This is in preparation for indexing all metadata.
After moving all of the times to the index, there should be far fewer
unique instances of the remaining metadata in many/most cases.

Change the index and index-related code to handle all time
values as integer nanoseconds since the epoch, excepting the packed
format, which (as mentioned above) is now an xstat timespec.

After these changes the index-related in-memory and on-disk time value
handling should match that of the metadata code (i.e. metadata.py,
.bupm, etc.).

Signed-off-by: Rob Browning <rlb@defaultvalue.org>
Remove tmax; should be unnecessary with high resolution timestamps.

This effectively reverses 7956f4eb2646d6ff9d56e62ef9e09e8d4763bb46.

Signed-off-by: Rob Browning <rlb@defaultvalue.org>
Store metadata in the index, in bupindex.meta; only store unique values.

FIXME: add the relevant information to DESIGN (and any suitable code
comments) before adding this to master.

Signed-off-by: Rob Browning <rlb@defaultvalue.org>
Move bup index's tick to the correct place; document related risks.

Put bup index's tick *after* update_index(), where it belongs, and
document the risks involved in modifying the filesytem during an index
run, or within too close proximity.

Signed-off-by: Rob Browning <rlb@defaultvalue.org>
Add the filename/fd and invalid value to stat_struc_to_py error messages.

Thanks to Nathan Bird <ecthellion@gmail.com> for the initial report.

Signed-off-by: Rob Browning <rlb@defaultvalue.org>