Speed up "zfs list" on systems with lots of fs / snapshots

[kaazoo]

getsnapshotsfordatasetandhost() in JNX/ZFS.pm calls "zfs list -t snapshot" which is slow on systems with lots of fs and snapshots.

To me it looks like the function only requires the name of the snapshots and not all their metadata. So instead "zfs list -t snapshot -o name -s name" should be used.

On a production system with 697 filesystems and 7322 snapshots I get the following run times:

time zfs list -t snapshot -o name -s name >/dev/null

real  0m19.904s
user  0m0.224s
sys   0m1.336s

time zfs list -t snapshot >/dev/null

real  2m16.485s
user  0m0.712s
sys   0m4.540s

See openzfs/zfs#450 for reference.

[jollyjinx]

Thanx for pointing this out ! It's fixed now.