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+
+% Registration Block Devices and Transport Classes: Where are we
+% going?
+% Proposal James Bottomley (jejb@steeleye.com)
+
+A transport class is quite simply a device driver
+helper library with an associated sysfs component.
+Although this sounds deceptively simple, in practise it
+allows fairly large simplifications in device driver
+code. Up until recently, transport classes were
+restricted to be SCSI only, but now they can be made to
+apply to any device driver at all (including ones with
+no actual transports).
+
+The need for a transport class comes into most device
+driver subsystems that drive a class of devices. SCSI
+is a really good example of this: We have a core set of
+APIs which are needed by every SCSI driver (whether
+Parallel SCSI, Fibre Channel or something even more
+exotic) to do with queueing commands and interpreting
+status codes. However, there were a large number of
+ancillary services which don't apply to the whole of
+SCSI, like Domain Validation for Parallel SCSI or
+target disconnection/reconnection for Fibre Channel.
+The sysfs exposure gives the user a well known way to
+control device parameters (like period and offset, for
+parallel SCSI) without having to develop a core SCSI
+API. Since a transport class has only a sysfs interface
+and a driver API, it is completely independent of the
+SCSI core. This makes the classes arbitrarily
+extensible and imposes no limit on how many may be
+simultaneously present.
+
+This talk will examine the evolution of the transport
+class in SCSI, covering its current uses in Parallel
+SCSI (SPI), Fibre Channel (FC) and other transports
+(iSCSI and SAS), contrasting it with previous
+approaches, like CAM, and follow with a description of
+how the concept was freed from the SCSI subsystem and
+how it could be applied in other aspects of kernel
+development, particularly block devices.
personal git repositories of Harald Welte. Your mileage may vary