Switch from zfs get to zfs list calls for better performance

[amitkris]

Hi,

This issue is in conjunction with #39.
In an effort to come up with a PR for Solaris support I investigated performance on using zfs list instead of zfs get and came up with the following numbers on Linux.
In short zfs list is quicker, especially when retrieving a specific set of properties.

I wrote a small timer function using the go "time" package that would time zfs Init().
On a Ubuntu system that had 40 containers on it: (As the number of containers on the system increases the time difference also increases drastically)
Without my changes daemon startup showed ZFS init took:

root:~/docker# ./docker-1.11.0-dev-baseline daemon --storage-driver=zfs
ZFS driver init took 716.156429ms time
INFO[0000] Graph migration to content-addressability took 0.00 seconds 
INFO[0000] Firewalld running: false  
INFO[0001] Default bridge (docker0) is assigned with an IP address 172.17.0.0/16. Daemon option --bip can be used to set a preferred IP address 
WARN[0001] Your kernel does not support swap memory limit. 
INFO[0001] Loading containers: start.  
INFO[0002] Loading containers: done.  
INFO[0002] Daemon has completed initialization  
INFO[0002] Docker daemon                                 commit=d687023-unsupported execdriver=native-0.2 graphdriver=zfs version=1.11.0-dev
INFO[0002] API listen on /var/run/docker.sock           

With my changes:

root@:~/docker# bundles/1.11.0-dev/binary/docker-1.11.0-dev daemon --storage-driver=zfs
ZFS driver init took 282.353825ms time
INFO[0000] Graph migration to content-addressability took 0.00 seconds 
INFO[0000] Firewalld running: false  
INFO[0000] Default bridge (docker0) is assigned with an IP address 172.17.0.0/16. Daemon option --bip can be used to set a preferred IP address 
WARN[0001] Your kernel does not support swap memory limit. 
INFO[0001] Loading containers: start.  
INFO[0001] Loading containers: done.  
INFO[0001] Daemon has completed initialization  
INFO[0001] Docker daemon                                 commit=d687023-unsupported execdriver=native-0.2 graphdriver=zfs version=1.11.0-dev
INFO[0001] API listen on /var/run/docker.sock           

Also zfs_test,go does a good job of running all the ZFS commands supported and in all we saved almost 6s on the test run with the changes:

root@:~/vendor/src/github.com/mistifyio/go-zfs# go test
PASS
ok      github.com/mistifyio/go-zfs 20.738s
root@:~/vendor/src/github.com/amitkris/go-zfs# go test
PASS
ok      github.com/amitkris/go-zfs  14.677s

Container startup time is still comparable:

root@:~/docker# time bundles/1.11.0-dev/binary/docker-1.11.0-dev run -i ubuntu /bin/true

real    0m2.368s
user    0m0.104s
sys 0m0.008s
root@:~/docker# time ./docker-1.11.0-dev-baseline run -ti ubuntu /bin/true

real    0m2.039s
user    0m0.076s
sys 0m0.020s

CHANGES made:

1. Replace zfs/zpool get calls with zfs/zpool list
2. Specify the list of relevant properties using -o instead of just calling all
3. Changing parseLine to handle output of list instead of get
4. Make all the dataset and zpool struct elements strings instead of (strings + integers) because they are being consumed as strings in the graphdriver in Docker anyway( we're going from string->uint64->string, why not just store them as strings..)

[mmlb]

Fixed by #41