[Stgt-devel] User-mode iSER

[Tom Tucker]

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?

> 
> 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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> > Stgt-devel at lists.berlios.de
> > http://bat.berlios.de/mailman/listinfo/stgt-devel
> 
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