targetclid: add daemonize component for targetcli

Problem:
-------
Overall creation time of a block using targetcli is raising linearly as the
block count increase.

This is because of the recurring issue involving refresh(reload) at
multiple objects/places, as the LIO's configfs is deeply nested.

Earlier discussion of the problem statement with stats and graphs about delays:
http://bit.ly/targetcli-create-delay

Solution:
--------
Introduce a daemon component for targetcli[d] which will retain state of
Configshell object in memory, so that any new requests can directly use it,
instead of loading the storageObjects/targetObjects again.

Details about "how to use it ?":
-------------------------------

$ systemctl start targetclid

$ systemctl status targetclid
● targetclid.service - Targetcli daemon
   Loaded: loaded (/usr/lib/systemd/system/targetclid.service; disabled; vendor preset: disabled)
   Active: active (running) since Wed 2019-04-10 12:19:51 IST; 2h 17min ago
 Main PID: 3950 (targetclid)
    Tasks: 3 (limit: 4915)
   CGroup: /system.slice/targetclid.service
           └─3950 /usr/bin/python /usr/bin/targetclid

Apr 10 12:19:51 localhost.localdomain systemd[1]: Started Targetcli daemon.

$ targetcli help
Usage: /usr/bin/targetcli [--version|--help|CMD|--tcp]
  --version		Print version
  --help		Print this information
  CMD			Run targetcli shell command and exit
  <nothing>		Enter configuration shell
  --tcp CMD		Pass targetcli command to targetclid
  --tcp <nothing>	Enter multi-line command mode for targetclid
See man page for more information.

One line command usage:
----------------------
$ targetcli --tcp CMD

Eg:
$ targetcli --tcp pwd
/

Multiple line commands usage:
----------------------------
$ targetcli --tcp
CMD1
CMD2
.
.
CMDN
exit

Eg:
$ targetcli --tcp
^Tab
/              backstores/    iscsi/         loopback/      vhost/         xen-pvscsi/    cd
clearconfig    exit           get            help           ls             pwd            refresh
restoreconfig  saveconfig     set            status

pwd
get global logfile
get global auto_save_on_exit
/ saveconfig
exit

output follows:
/
logfile=/var/log/gluster-block/gluster-block-configshell.log
auto_save_on_exit=false
Configuration saved to /etc/target/saveconfig.json

Stats with and without changes:
------------------------------

Running simple 'pwd' command after creating 1000 blocks on a node:

Without this change:

$ time targetcli pwd
/

real    0m8.963s
user    0m7.775s
sys     0m1.103s

with daemonize changes:

$ time targetcli --tcp "pwd"
/

real    0m0.126s
user    0m0.099s
sys     0m0.024s

Thanks to Maurizio for hangingout with me for all the discussions involved.

Signed-off-by: Prasanna Kumar Kalever <prasanna.kalever@redhat.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/systemd/targetclid.service b/systemd/targetclid.service
new file mode 100644
index 0000000..2de9100
--- /dev/null
+++ b/systemd/targetclid.service
@@ -0,0 +1,10 @@
+[Unit]
+Description=Targetcli daemon
+
+[Service]
+Type=simple
+ExecStart=/usr/bin/targetclid
+Restart=on-failure
+
+[Install]
+WantedBy=multi-user.target