Customize number of snapshots per filesystem

[mat813]

It would be nice if one could change the number of snapshot, doing something like:

$ zfs set com.sun:auto-snapshot:weekly=12 zroot/var/log

So the values would go from true/false to true/false/[0-9]+

[bdrewery]

This is more complex than it seems. The handling of zfs destroy -r for old snapshots would need logic to handle child datasets differently than parent ones. There is a lot of optimization for handling of recursive snapshots currently.