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    SubjectRe: [Scst-devel] Fwd: Re: linuxcon 2010...
    Nicholas A. Bellinger, on 08/20/2010 02:29 AM wrote:
    > "We will be extending the scsi_tgt_[lib,if].c mapped ring interface to
    > allow TCM to access userspace backstores transparently with existing
    > kernel level TCM fabric modules, and using the generic configfs fabric
    > module infrastructure in target_core_fabric_configfs.c for the port and
    > I_T nexus control plane just as you would with any TCM backstore
    > subsystem today.
    >
    > Again, in open source you have to build upon what already exists and
    > move forward. The original STGT kernel<-> userspace ring abstraction
    > and logic in drivers/scsi/scsi_tgt_lib.c:scsi_tgt_queue_command() ->
    > scsi_tgt_uspace_send_cmd() is already going to do the vast majority of
    > what is required for handling fabric I/O processing and I_T Nexus and
    > Port management in kernel space with a userspace backstore. It is
    > really just a matter of allowing the STGT ring request to optionally be
    > sent out to userspace as a standalone LUN instead of as a target port."

    You forgot to mention one small thing. You are going to (re)use current
    STGT interface for user space backend, which in 5 years of being
    mainline has not gained any noticeable interest, because it is
    fundamentally slow. It needs a complete redesign to become fast. In
    contrast, interface provided by scst_user has just 3% overhead comparing
    with fully in-kernel backend and allows to build storage capable of
    handling 1,500,000 IOPSes (Kaminario).

    Vlad


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