Remove support for man page generation using asciidoc "a2x": The
project is discontinued, and depends on Python 2.7.
As we will provide pre-generated man pages as of btrbk-0.28.0, this is
not needed any more.
With this, previous snapshots (far relations) are still listed when
restoring a snapshot.
Example (S = source subvolume, readwrite):
After 3 snapshots:
A->S, B->S, C->S
Restore B: `btrfs subvol delete S; btrfs subvol snapshot B S'`
A->S, B->S, C->S, S'->B
Previous implementation would show now snapshots for S', as no
snapshot has parent_uuid=S'.
New implementation shows A, B, C as snapshots for S', as orphaned
siblings (A, B, C pointing to deleted S) are also related.
Makes sure that if, for whatever reason, a subvolume having correct
btrbk name scheme does NOT share any extents with previous snapshots
is never used as parent.
Note that if a related parent is found, the unrelated closest
older/newer (by btrbk timestamp) subvolumes are still added as clone
sources.
Preferences for parent (and required clone sources):
1. closest older in snapdir (by btrbk timestamp), related
2. closest older related (by cgen)
3. closest newer related (by cgen)
4. closest older in snapdir (by btrbk timestamp)
5. closest newer in snapdir (by btrbk timestamp)
Note: prefering 1 over 2 helps keeping parent-chain within droot on
target (assuming that btrfs always uses correlated parent on
btrfs-receive).
This will e.g. add a clone source on "btrbk resume", if both older AND
newer snapshot/backup pairs exists.
Also makes sure that the closest older btrbk snapshot is always added
as clone source, even if another related subvolume has newer cgen.
Old implementation was missing last readonly parent in chain, as well
as orphaned siblings.
Also sort all by cgen, not by distance, then cgen.
Also skip self.
Allowed values for "incremental_resolve":
- "mountpoint" (default): Use parents in the filesystem tree below
mount points of source `<volume-directory>/<snapshot-dir>` and
target `<target-directory>`.
- "directory": Use parents strictly below source/target
directories. Useful when restricting access, e.g. when using
ssh_filter_btrbk.sh.
- "_all_accessible" (experimental): Use parents from all mount points.
Note that using "_all_accessible" causes btrfs-progs to fail:
- btrfs send -p: "ERROR: not on mount point: /path/to/mountpoint"
- btrfs receive: "ERROR: parent subvol is not reachable from inside the root subvol"
see also: https://github.com/kdave/btrfs-progs/issues/96
Axel Burri