Re: [LSF/MM TOPIC] Unifying the LIO and SCST target drivers

[Hannes Reinecke <hare@suse.de>]

On 01/14/2015 11:05 AM, Bart Van Assche wrote:
> The LIO and SCST SCSI target subsystems consist of the following components:
> * A core that processes SCSI commands and that provides common
> functionality like persistent reservations, LUN masking and an interface
> that allows configuration from user space.
> * Device handlers that allow this core to access SCSI devices, block
> devices and files uniformly as SCSI devices.
> * Target drivers that implement a storage protocol (iSCSI, FC, SRP,
> iSER, FCoE, ...) and that realize the SCSI request and response
> communication between the target system and an initiator system.
> 
> A significant amount of code is shared between several LIO target
> drivers and the SCST target drivers that implement the same storage
> protocol. Since there are two sets of these drivers this means that each
> set has to be maintained, extended and tested separately. This means a
> lot of redundant work. The main difference between these two sets of
> drivers is the interface between the target drivers and the SCSI target
> core.  Hence the proposal to discuss the unification of the API between
> SCSI target core and SCSI target drivers. Implementing a single unified
> API would have the following advantages:
> * A single set of target drivers works for both projects which means a
> reduction of the maintenance effort for those who maintain target
> drivers for target driver developers and target driver users.
> * This would increase the size of the user base for the unified target
> drivers.
> * This would reduce the workload for the storage target maintainers.
> * This would motivate the SCST target driver maintainers to contribute
> to the upstream target drivers and to bring the upstream SRP and FCoE
> target drivers to the same feature and stability level as their SCST
> counterparts. In other words, the LIO users would also benefit from this
> work.
> * This effort would also help SCST users by ensuring that all latest
> target driver features are also available to SCST users. Some time ago
> (but no longer today) the LIO QLogic target driver was ahead of the SCST
> QLogic target driver. This motivated an SCST user to port the LIO QLogic
> target driver to SCST. See also Greg Wettstein, New release of
> SCST/Qlogic target interface driver, linux-scsi, April 2014,
> http://marc.info/?l=linux-scsi&m=139649571807085).
> 
> During the first phase of this initiative the focus will be on the
> QLogic FC, SRP and FCoE target drivers since a significant part of the
> code of these drivers is shared between the two target frameworks.
> 
> For those who are not following the SCST project: I'm maintaining the
> SCST SRP and FCoE target drivers.
> 
> Nic, in case it was not yet clear, you would be more than welcome during
> this session :-)
> 
I'd like to have this discussion, too.

It would be really good if we can make that work; after all, Linux
should be about _choice_. So if both parties agree to have this
discussion I'm all for it.
I can even act as a moderator if required :-)

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		               zSeries & Storage
hare@suse.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
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