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Browse Prior Art Database

Device Driver Synchronous Plot Option

IP.com Disclosure Number: IPCOM000060235D
Original Publication Date: 1986-Mar-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Chen, JN: AUTHOR [+4]

Abstract

A method is described to output data directly from a user program to an output device without intermediate copying of data. Traditionally, in the UNIX* operating system, kernel drivers for character devices, such as printers, would copy data on a write system call from the program to an intermediate buffer in the kernel before outputting the data to the printer. The intermediate buffers consist of many small blocks of memory, each 64 bytes long. These blocks are collectively referred to as character lists. the overhead of copying data from the program buffer to the character list, and the overhead of linking all the character lists together can become significant when driving high speed printers. It is desirable to avoid this copying of data if possible.

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Device Driver Synchronous Plot Option

A method is described to output data directly from a user program to an output device without intermediate copying of data. Traditionally, in the UNIX* operating system, kernel drivers for character devices, such as printers, would copy data on a write system call from the program to an intermediate buffer in the kernel before outputting the data to the printer. The intermediate buffers consist of many small blocks of memory, each 64 bytes long. These blocks are collectively referred to as character lists. the overhead of copying data from the program buffer to the character list, and the overhead of linking all the character lists together can become significant when driving high speed printers. It is desirable to avoid this copying of data if possible. The details of the method are described for the UNIX operating system which is running as a virtual machine on the Virtual Resource Manager (VRM) control program. The VRM control program is similar in concept to the IBM VM/370 control program. A program which desires to write large amounts of already formatted data to a printer may avoid the intermediate copy on the write system call by first specifying two simultaneous modes of operation. Synchronous mode is specified, which means that the program does not receive control from the write system call until the output is complete. Also, plot mode is specified, which means that the data is not to be modified in any way. The UNIX...