Add suport for other iscsi transports beside tcp

https://blueprints.launchpad.net/nova/+spec/add-open-iscsi-transport-support

Change-Id: I9a8190441c4abb259898915cfe453ce6f43d6d8e

specs/kilo/approved/support-other-iscsi-transports-besides-tcp.rst

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+..
+ This work is licensed under a Creative Commons Attribution 3.0 Unported
+ License.
+
+ http://creativecommons.org/licenses/by/3.0/legalcode
+
+====================================================================
+ Refactor ISCSIDriver to support other iSCSI transports besides TCP
+====================================================================
+
+
+https://blueprints.launchpad.net/nova/+spec/add-transport-support-to-iscsi
+
+Currently open-iscsi in openstack does not allow the use of offload iscsi
+transports (cxgb4i, qla4xx, bnx2i etc) or other software iscsi transports
+(like iser). This blueprint aims to add support for this
+
+Problem description
+===================
+
+open-iscsi has hardware iSCSI transport support. The interface argument
+specifies the hardware iSCSI interface to use for the operation. Any hardware
+vendors that currently  provide hardware interfaces for open-iscsi cannot use
+them in  openstack as the interfaces (iface) argument is not currently
+supported in the iSCSI driver.
+
+While this effort is being done by Chelsio, the approach is currently to make
+it generic enough for all supported HBAs (Host Bus Adapter).
+
+Use of such iSCSI hardware transports requires providing a corresponding
+interface file (referred to as iface), which can be autogenerated via iscsiadm
+but need correctness checks or can also be generated on the fly, given the
+3-tuple of ipaddress, hwaddress & transport name to be used. The iface format
+itself is generic and does not use any propreitary fields irrespective of
+transport being used.
+
+This also addresses a second problem with the current transport support in
+nova, namely the iSER driver. It is currently a full copy of the normal
+open-iscsi driver code with an extra parameter setting transport to 'iser'
+
+This will also enable use of iSER directly through the iSCSI driver, though
+deprecating the iSER driver is not the aim of this spec, and will probably
+start with iSER disabled, (and also because iSER requires target support
+unlike hardware transports) Previous relevant specs are here :
+
+https://review.openstack.org/#/c/86637/
+
+https://blueprints.launchpad.net/nova/+spec/add-transport-support-to-iscsi
+
+https://blueprints.launchpad.net/cinder/+spec/add-transport-support-to-iscsi
+
+A follow up blueprint is expected to deprecate the separate iSER driver
+and just roll functionality into using transport support.
+
+Use Cases
+----------
+
+User has an HBA that supports hardware iSCSI installed in his system. Using
+open-iscsi's hardware transport support allows for iSCSI communication at
+higher speeds and reduced CPU usage.
+
+Current transports supported by open-iscsi are :
+
+* Chelsio : cxgb3i, cxgb4i
+
+* QLogic : qla4xxx, bnx2i (formerly Broadcom)
+
+* Emulex : be2iscsi, ocs
+
+* Mellanox & others : iser
+
+Use of any of these transports requires the appropriate hardware to be present
+in the system, but iSER will not be supported at the very start.
+
+Project Priority
+-----------------
+
+None
+
+Proposed change
+===============
+
+On the initiator side the only difference between using software iSCSI and
+hardware iSCSI transport is the interface flag (--interface=[iface])
+
+e.g. "iscsiadm -m discovery -t st -p ip:port -I <iface file>"
+
+iface files can automatically be generated for all hardware present on a
+system that is supported by open-iscsi by 'iscsiadm -m iface'. The default
+format for iface file names is in the form <transport_name.hw_address>
+
+The default iface name is 'default'. Not using the -I parameter (which is how
+open-iscsi  is currently being used in nova) is the same as specifying
+
+'iscsiadm -m discovery -t st -p ip:port -I default'
+
+Required changes are :
+
+* A new parameter to specify which transport should be used while doing iscsi
+  discovery/login, falling back to TCP if operation does not succeed, or if
+  parameter is not provided (-I default)
+* An alternative (but lot more complicated ) approach might be to figure out
+  iface name from source ip address. ipaddress can be used to figure out
+  hwaddress and pci dev id. pci dev id provides transport name, iface names
+  are in the format <transportname>.<hwaddress>
+* Optional/unresearched : Further down the line, it might make sense to see
+  if networking services can be integrated to provide a networking interface
+  for open-iscsi transports, but its out of the scope of this spec.
+
+Other related changes :
+
+* Verify hardware exists before attempting to use said transport. The best
+  way to accomplish this is checking PCI vendor ids/MAC address if nova would
+  be open to accepting such code.
+
+Alternatives
+------------
+
+Use manual discovery of iscsi-targets, and provide -I parameter when doing
+discovery. Transport names are written in the resultant records generated by
+open-iscsi, however this does not guarantee hardware transports will be used,
+as this can be overridden with depending on how cli params are constructed.
+
+Data model impact
+-----------------
+
+None
+
+REST API impact
+---------------
+
+None
+
+Security impact
+---------------
+
+None
+
+Notifications impact
+--------------------
+
+None
+
+Other end user impact
+---------------------
+
+
+Performance Impact
+------------------
+
+iSCSI performance is improved drastically, no extra commands are added to
+driver, except perhaps one to generate the default iface files :
+'iscsiadm -m iface'
+
+Other deployer impact
+---------------------
+
+This can be used as a stepping stone to eventually replace & deprecate
+LibvirtISERVolumeDriver as  'iscsiadm -I iser' can be used for iSER support
+without requiring a separate driver.
+
+Developer impact
+----------------
+
+None
+
+Implementation
+==============
+
+Assignee(s)
+-----------
+
+Primary assignee:
+  anish7 <anish@chelsio.com>
+
+iSER driver deprecation & followup spec Assignee :
+
+  aviramb <aviramb@mellanox.com>
+
+  nuritv <nuritv@mellanox.com>
+
+Work Items
+----------
+
+* Add -I parameter to all iscsiadm login/discovery commands in
+  'nova/virt/libvirt/volume.py'
+* Add transport parameter to config options, which defaults to software iscsi
+  i.e. '-I default'
+
+Dependencies
+============
+
+None as such. However, the minimum information required for using a tansport
+if it is not already configured is a 3 tuple of ip, transport name & hardware
+address. Functionality to this effect would be good to have for automatic
+configuration of transports.
+
+Testing
+=======
+
+Current iSCSI tests will work just fine. Will be testing on Chelsio hardware,
+and any other transport supporting hardware that can be obtained.
+
+Documentation Impact
+====================
+
+New transport parameter will need relevant documentation.
+
+References
+==========
+
+* http://www.open-iscsi.org/docs/README (Section 5.1 iSCSI iface setup)
+
+* http://red.ht/1BJxsjL (Configuring an iface for iSCSI Offload, RedHat documentation)