80 lines
1.7 KiB
C
80 lines
1.7 KiB
C
/* This file is part of the sample code and exercises
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* used by the class "Advanced Programming in the UNIX
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* Environment" taught by Jan Schaumann
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* <jschauma@netmeister.org> at Stevens Institute of
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* Technology.
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*
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* This file is in the public domain.
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*
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* You don't have to, but if you feel like
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* acknowledging where you got this code, you may
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* reference me by name, email address, or point
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* people to the course website:
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* https://stevens.netmeister.org/631/
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*/
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/* simple-cat.c, O_SYNC version
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*
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* Use this program to illustrate the use of fcntl(2)
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* to set the O_SYNC flag on STDOUT, which we do not
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* open ourselves, so can't set that flag on at that
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* time.
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*
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* This also illustrates the difference between
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* synchronous and asynchronous I/O:
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*
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* Create a large enough file:
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*
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* dd if=/dev/zero of=file bs=$((1024 * 1024)) count=25
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*
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* Then run this program:
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*
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* time ./a.out <file >out
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*
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* Then, comment out the setting of O_SYNC, recompile
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* the program and run it again.
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*/
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#include <fcntl.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <unistd.h>
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#define BUFFSIZE 512
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int
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main(int argc, char **argv) {
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int n;
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char buf[BUFFSIZE];
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int flags;
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/* cast to void to silence compiler warnings */
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(void)argc;
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(void)argv;
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if ((flags = fcntl(STDOUT_FILENO, F_GETFL, 0)) < 0) {
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perror("Can't get file descriptor flags");
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exit(EXIT_FAILURE);
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}
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//flags |= O_SYNC;
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if (fcntl(STDOUT_FILENO, F_SETFL, flags) < 0) {
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perror("Can't set file descriptor flags");
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exit(EXIT_FAILURE);
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}
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while ((n = read(STDIN_FILENO, buf, BUFFSIZE)) > 0 )
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if ( write(STDOUT_FILENO, buf, n) != n ) {
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perror("write error");
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exit(EXIT_FAILURE);
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}
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if (n < 0) {
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perror("read error");
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exit(EXIT_FAILURE);
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}
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return EXIT_SUCCESS;
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}
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