The Placement of File Sub-system Data Streams
Baras, John S.
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An abstraction called Cues was implemented  for providing data streams over the file sub-system in the Unix kernel. The data stream of a Cue can be used for transfer of data as well as for control of the data stream by composing such structures. The algorithm for scheduling the compound Cue sequences read and write operations for data and control Cues in the kernel and retains other properties of user process driven read-write. This is possible for the data stream as this abstraction is over the file sub-system and the data stream is run in the context of the user process that created the Cue. This report reconsiders the architectural placement of the Cues, based on the experience with design and text of implementations. The underlying theme is to try to keep the control and flexibility as it is with user processes and keep from tying it in the kernel or user space unless specifically required, in effect re-evaluating the placement of the implementation in the kernel.