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

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On 1/14/15, 2:05 AM, "Bart Van Assche" <bart.vanassche@xxxxxxxxxxx> 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 :-)
>
>Bart.

QT> +1.  This would be a plus for Qlogic to have 2 stacks under a unify
API.  Test resource & devlopment cycles are limited.  A lot of cycles are
loss in keeping patches in sync.

Would like to listen in at LSF to hear the discussion.

<<attachment: winmail.dat>>


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