OpenZFS 8600 - ZFS channel programs - snapshot

Authored by: Chris Williamson <chris.williamson@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: John Kennedy <john.kennedy@delphix.com>
Reviewed by: Brad Lewis <brad.lewis@delphix.com>
Approved by: Robert Mustacchi <rm@joyent.com>
Ported-by: Don Brady <don.brady@delphix.com>

ZFS channel programs should be able to create snapshots.
In addition to the base snapshot functionality, this entails extra
logic to handle edge cases which were formerly not possible, such as
creating then destroying a snapshot in the same transaction sync.

OpenZFS-issue: https://www.illumos.org/issues/8600
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/68089b8b

man/man8/zfs-program.8

@@ -372,6 +372,18 @@ filesystem (string)
 .Bd -ragged -compact -offset "xxxx"
 Filesystem to rollback.
 .Ed
+.It Em zfs.sync.snapshot(dataset)
+Create a snapshot of a filesystem.
+Returns 0 if the snapshot was successfully created,
+and a nonzero error code otherwise.
+.Pp
+Note: Taking a snapshot will fail on any pool older than legacy version 27.
+To enable taking snapshots from ZCP scripts, the pool must be upgraded.
+.Pp
+dataset (string)
+.Bd -ragged -compact -offset "xxxx"
+Name of snapshot to create.
+.Ed
 .El
 .It Sy zfs.check submodule
 For each function in the zfs.sync submodule, there is a corresponding zfs.check
@@ -392,6 +404,7 @@ The available zfs.check functions are:
 .It Em zfs.check.destroy(dataset, [defer=true|false])
 .It Em zfs.check.promote(dataset)
 .It Em zfs.check.rollback(filesystem)
+.It Em zfs.check.snapshot(dataset)
 .El
 .It Sy zfs.list submodule
 The zfs.list submodule provides functions for iterating over datasets and