Add channel program for property based snapshots

Channel programs that many users find useful should be included with zfs
in the /contrib directory. This is the first of these contributions. A
channel program to recursively take snapshots of datasets with the
property com.sun:auto-snapshot=true.

Reviewed-by: Kash Pande <kash@tripleback.net>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Clint Armstrong <clint@clintarmstrong.net>
Closes openzfs#8443
Closes openzfs#9050

configure.ac

@@ -135,6 +135,7 @@ AC_CONFIG_FILES([
 	contrib/initramfs/scripts/local-top/Makefile
 	contrib/pyzfs/Makefile
 	contrib/pyzfs/setup.py
+	contrib/zcp/Makefile
 	module/Makefile
 	module/avl/Makefile
 	module/nvpair/Makefile

contrib/Makefile.am

@@ -1,2 +1,2 @@
-SUBDIRS = bash_completion.d dracut initramfs pyzfs
-DIST_SUBDIRS = bash_completion.d dracut initramfs pyzfs
+SUBDIRS = bash_completion.d dracut initramfs pyzfs zcp
+DIST_SUBDIRS = bash_completion.d dracut initramfs pyzfs zcp

contrib/zcp/Makefile.am

@@ -0,0 +1 @@
++EXTRA_DIST = autosnap.lua

contrib/zcp/autosnap.lua

@@ -0,0 +1,75 @@
+-- Recursively snapshot every dataset with a given property
+--
+-- Usage: zfs program <pool> autosnap.lua -- [-n] [-p <property>] <snapshot>
+
+results = {}
+
+args = ...
+argv = args["argv"]
+usage = [[
+
+
+usage: zfs program <pool> autosnap.lua -- [-n] [-p <property>] <snapshot>
+
+	-n: performs checks only, does not take snapshots
+	-p <property>: property to check. [default: com.sun:auto-snapshot]
+	<snapshot>: root snapshot to create [example: tank/data@backup]
+]]
+
+property = "com.sun:auto-snapshot"
+noop = false
+root_snap = nil
+
+for i, arg in ipairs(argv) do
+	if arg == "-n" then
+		noop = true
+	elseif arg == "-p" then
+	elseif argv[i-1] == "-p" then
+		property = arg
+	else
+		root_snap = arg
+	end
+end
+
+if root_snap == nil or property == nil then
+	error(usage)
+end
+
+root_ds_name = ""
+snap_name = ""
+for i = 1, #root_snap do
+	if root_snap:sub(i, i) == "@" then
+		root_ds_name = root_snap:sub(1, i-1)
+		snap_name = root_snap:sub(i+1, root_snap:len())
+	end
+end
+
+function auto_snap(root)
+	auto, source = zfs.get_prop(root, property)
+	if auto == "true" then
+		ds_snap_name = root .. "@" .. snap_name
+		err = 0
+		if noop then
+			err = zfs.check.snapshot(ds_snap_name)
+		else
+			err = zfs.sync.snapshot(ds_snap_name)
+		end
+		results[ds_snap_name] = err
+	end
+	for child in zfs.list.children(root) do
+		auto_snap(child)
+	end
+end
+
+auto_snap(root_ds_name)
+err_txt = ""
+for ds, err in pairs(results) do
+	if err ~= 0 then
+		err_txt = err_txt .. "failed to create " .. ds .. ": " .. err .. "\n"
+	end
+end
+if err_txt ~= "" then
+	error(err_txt)
+end
+
+return results