As described in the summary. From Mark in linked:

Docs:
db.serverStatus() for mongos now includes metrics for cursors. The goal is to remove the deprecated cursorInfo command in the release after 2.8.

Example:

mongos> db.serverStatus()
{
	"metrics" : {
		"cursor" : {
			"open" : {
				"multiTarget" : NumberLong(0),
				"singleTarget" : NumberLong(0),
				"total" : NumberLong(0)
			}
		},
	},
	"ok" : 1
}

multiTarget - this is for multi-shard cursors.
singleTarget - this is for single shard cursors.
total - sum of singleTarget, and multiTarget