Книга: Distributed operating systems

9.5.1. Structure of a UNIX Process

9.5.1. Structure of a UNIX Process

A UNIX process runs as a Chorus user process, on top of the UNIX subsystem. As such, it has all the features of a Chorus process, although existing UNIX programs will not use all of them. The standard text, data, and stack segments are implemented by three mapped Chorus segments.

On the whole, the way Chorus works is not hidden from the UNIX runtime system and library (although it is hidden from the program). For example, when the program wants to open a file, the library procedure open invokes the subsystem, which ultimately gets a file capability. It stores the file capability internal to itself and uses it when the user process calls read, write, and other procedures that deal with the open file.

Open files are not the only UNIX concepts that are mapped onto Chorus resources. Open directories (including the working directory and root directory), open devices, pipes, and in-use segments are all represented internally as capabilities for the corresponding Chorus resources. Operations on all of these are done by the UNIX subsystem by passing the capability to the appropriate server. To remain binary compatible with UNIX, the user process must never see the capabilities.

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