name matter of tpgt_1/lun/lun_0/<link2iblock> ?

[Oliver Rath]

Hi list,

I try to reproduce the creating of an iscsi-target via iblock device as
shown in lio_node and tcm_node. Taken from
http://www.thomas-krenn.com/de/wiki/Linux-IO_Target_%28LIO%29_unter_Ubuntu_14.04#FILEIO_.28Linux_VFS_devices.29
with targetcli:


|cd /backstores/iblock|
|create name=iscsi dev=/dev/sdb|
|cd /iscsi|
create
|cd
iscsi/***@dmicrash:iqn.2003-01.org.linux-iscsi.dmicrash.x8664:sn.a5bb4cf3e6cd/tpgt1/portals
# in my case
create
cd ../luns|
create /backstores/iblock/iscsi
# works fine, but here is my question point

Now I tried the same with generic commands:
cd /sys/kernel/config/target/core/
mkdir iblock_1
cd iblock_1
mkdir iblock_clone6/
echo "udev_path=/dev/myvg/clone6" > control
echo -n 1 > enable

# Now we can create the iscsi-Target

cd cd /sys/kernel/config/target/iscsi/
mkdir iqn.2012-03.org.clone6.liotarget
cd iqn.2012-03.org.clone6.liotarget
mkdir tpgt_1
cd tpgt_1
mkdir -p tpgt_1/lun/lun_0
cd tpgt_1/lun/lun_0
---- break ----
Here exists in the dir made by targetcli a link with the name
"81eb98828f", which points to the iblock device. This seems to be a 5
byte hex-number.
Now my question: How is this number generated? Does the name matter for
functionality? It seems there a separate number for all links. Im able
to create the link with my own name and all seems ok.
--- break end ---
ln -s ../../../../../../target/core/iblock_1/iblock_clone6/ my_own_link
cd ../../np
mkdir '192.168.96.254:3260'
cd ..
echo 1 > enable


This all works and the output in targetcli shows me an enabled target
pointing to /dev/myvg/clone6.

Is this a possible alternative to generate a target. Do I have to
prepare a special name for this link?

Tfh!
Oliver

[Nicholas A. Bellinger]

Hi Oliver,

Post by Oliver Rath
Hi list,
I try to reproduce the creating of an iscsi-target via iblock device as
shown in lio_node and tcm_node. Taken from
http://www.thomas-krenn.com/de/wiki/Linux-IO_Target_%28LIO%29_unter_Ubuntu_14.04#FILEIO_.28Linux_VFS_devices.29
|cd /backstores/iblock|
|create name=iscsi dev=/dev/sdb|
|cd /iscsi|
create
|cd
# in my case
create
cd ../luns|
create /backstores/iblock/iscsi
# works fine, but here is my question point
cd /sys/kernel/config/target/core/
mkdir iblock_1
cd iblock_1
mkdir iblock_clone6/
echo "udev_path=/dev/myvg/clone6" > control
echo -n 1 > enable
# Now we can create the iscsi-Target
cd cd /sys/kernel/config/target/iscsi/
mkdir iqn.2012-03.org.clone6.liotarget
cd iqn.2012-03.org.clone6.liotarget
mkdir tpgt_1
cd tpgt_1
mkdir -p tpgt_1/lun/lun_0
cd tpgt_1/lun/lun_0
---- break ----
Here exists in the dir made by targetcli a link with the name
"81eb98828f", which points to the iblock device. This seems to be a 5
byte hex-number.
Now my question: How is this number generated? Does the name matter for
functionality? It seems there a separate number for all links. Im able
to create the link with my own name and all seems ok.
--- break end ---
ln -s ../../../../../../target/core/iblock_1/iblock_clone6/ my_own_link
cd ../../np
mkdir '192.168.96.254:3260'
cd ..
echo 1 > enable
This all works and the output in targetcli shows me an enabled target
pointing to /dev/myvg/clone6.
Is this a possible alternative to generate a target. Do I have to
prepare a special name for this link?

The LUN configfs symlink destination name is created from a uuid in the
following rtslib code:

https://github.com/Datera/rtslib/blob/master/rtslib/target.py#L407

There is no hard requirement from the kernel side for this to be a
unique value, and IIRC is only used for indexing purposes by rtslib.

That said, I'd still recommend using rtslib and/or targetcli for driving
the configuration in real-world usage scenarios, beyond poking at
configfs directly to better understand how the underlying system
functions.

--nab

[Oliver Rath]

Hi Nicholas,

Post by Nicholas A. Bellinger
Hi Oliver,

[..]

The LUN configfs symlink destination name is created from a uuid in the
https://github.com/Datera/rtslib/blob/master/rtslib/target.py#L407
There is no hard requirement from the kernel side for this to be a
unique value, and IIRC is only used for indexing purposes by rtslib.
That said, I'd still recommend using rtslib and/or targetcli for driving
the configuration in real-world usage scenarios, beyond poking at
configfs directly to better understand how the underlying system
functions.

Thank you very much! This was the missing link for me!

Regards
Oliver