A bookmark with a well-known name is used to track which version was
last successfully received by the receiver.
The createtxg that can be retrieved from the bookmark using `zfs get` is
used to set the Replicated attribute of each snap on the sender:
If the snap's CreateTXG > the cursor's, it is not yet replicated,
otherwise it has been.
There is an optional config option to change the behvior to
`CreateTXG >= the cursor's`, and the implementation defaults to that.
The reason: While things work just fine with `CreateTXG > the cursor's`,
ZFS does not provide size estimates in a `zfs send` dry run
(see acd2418).
However, to enable the use case of keeping the snapshot only around for
the replication, the config flag exists.
Since we don't implement screen-scraping of ZFS output ATM, this is
better than nothing, as user's may be able to figure out what' sthe
problem from the logs / status reports.
Summary:
* Logging is still bad
* test output in a lot of placed
* FIXMEs every where
Test Plan: None, just review
Differential Revision: https://phabricator.cschwarz.com/D2
The old approach with ZFSList would keep the two-dimensional array of
lines and their fields in memory (for a short time), which could easily
consume 100s of MiB with > 10000 snapshots / bookmarks (see #34)
fixes#61
config defines a single datastructure that can act both as a Map and as a Filter
(DatasetMapFilter)
Cleanup wildcard syntax along the way (also changes semantics).
