[Stgt-devel] User-mode iSER
Tue Aug 1 21:56:20 CEST 2006
On Tue, 2006-08-01 at 14:00 -0500, Tom Tucker wrote:
> On Tue, 2006-08-01 at 14:49 -0400, Ming Zhang wrote:
> > my 2c. u figure ignores other device types like VT/VTL or bridge. your
> > target device type are only TYPE_DISK here.
> Yeah, I should put in ellipses... These types are not precluded.
> > also scsi/block/file just
> > physical media used by TYPE_DISK.
> Yes, but there seemed to be some interest in exporting a file as a SCSI
> Target, or even anonymously mapped memory...
> What else should we be thinking about?
what about the AoE? maybe people want AoE target as well. or AoE will
not be considered because of its non-SCSI nature?
> > Ming
> > On Tue, 2006-08-01 at 13:42 -0500, Tom Tucker wrote:
> > > What do people think about something like this...
> > >
> > > The target architecture is implemented to the extent possible entirely
> > > in user-mode. The architecture intends to support multiple Target Device
> > > Types, SCSI Transport Types and Network Transport Types. The enclosed
> > > figure below illustrates the components of the architecture.
> > >
> > > At the top of the figure are the different Target Device Type Drivers.
> > > These "drivers" are implemented in user-mode as libraries and plug into
> > > the Target Interface Layer. The Target Device Type drivers each support
> > > a particular class of device. For example, the SCSI Disk Driver supports
> > > SCSI disks, the Block Device driver supports generic block devices
> > > (e.g. /dev/md0, etc..) and the File Device Driver supports files as
> > > target devices. In most cases, the Target Device Type Drivers call
> > > existing system call interfaces to communicate with the actual target
> > > device, e.g. open, close, read, write, ioctl, etc... High performance
> > > implementations may use private kernel interfaces to improve
> > > performance.
> > >
> > > The Target Interface Layer implements a generic target device
> > > independent API called the Target Device API, and a SCSI transport
> > > independent API called the SCSI Transport API. This Target Interface
> > > Layer implements a target/SCSI transport switch that allows any Target
> > > Device Type to be associated with any SCSI Transport Type.
> > >
> > > The SCSI Transport Class Drivers implement support for the various SCSI
> > > transport types: SRP Transport implements the SCSI RDMA Protocol
> > > transport, FCP Transport implements the Fiber Channel transport type,
> > > and the iSCSI Transport implements the iSCSI transport type. These
> > > drivers sit between the Target Interface Layer and the Network Interface
> > > Layer.
> > >
> > > The Network Interface Layer implements a SCSI transport independent API
> > > called the Transport Class API and a network transport independent API
> > > called the Transport API. The Network Interface Layer allows a SCSI
> > > Transport Class driver to support multiple network transports. For
> > > example, the iSCSI Transport driver will support TCP, IB, and iWARP as
> > > network transports. The details of a particular SCSI Transport Class's
> > > device enumeration, login and management are implemented in the SCSI
> > > Transport Class driver (e.g. iSCSI Transport). The details of a
> > > particular network transport's connection management paradigm are
> > > implemented in the Transport Provider driver (e.g. RDMA driver).
> > >
> > > The Transport Provider Drivers implement the Transport Provider API and
> > > provide core network I/O services to the Network Interface Layer. The
> > > Transport API is a transport independent interface for creating
> > > endpoints, service points, accepting incoming connection requests and
> > > performing I/O on an endpoint.
> > >
> > > The Management Agent interfaces with the Target Interface Layer and
> > > performs management functions such as creating targets, devices, loading
> > > and storing persistent configurations and other management related
> > > functions.
> > >
> > > The various API referred to above are basically simplified versions of
> > > the existing scsi_transport_template, scsi_host, scsi_host_template
> > > interfaces, etc... from the current kernel implementation. The
> > > interfaces between the various components, however, can be reduced to
> > > function calls since everything resides user mode.
> > >
> > > I think the only tough issue here is with copy avoidance for the network
> > > user/kernel interface and target device user/kernel interfaces.
> > > Initially, these could be prototyped without regard to this issue and
> > > see what kind of performance we could get. The RDMA network transports
> > > already provide copy avoidance, however, TCP/FC would require some
> > > cleverness.
> > >
> > > Thoughts?
> > >
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