65 lines
1.5 KiB
C
65 lines
1.5 KiB
C
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/* 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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/*
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* This simple program creates a file with a hole in it, a so-called
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* sparse file. Use hexdump(1) or od(1) to verify that there is no data
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* in between the two strings; then copy the file to to another and
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* observe that the kernel supplied zeros to fill the hole.
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*/
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#include <sys/types.h>
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#include <sys/stat.h>
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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 <string.h>
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#include <unistd.h>
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char buf1[] = "abcdefghij";
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char buf2[] = "ABCDEFGHIJ";
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#define BIGNUM 10240000
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int
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main(void) {
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int fd;
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if ((fd = creat("file.hole", S_IRUSR | S_IWUSR)) < 0) {
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perror("creat error");
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return EXIT_FAILURE;
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}
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if (write(fd, buf1, strlen(buf1)) != sizeof(buf1) - 1) {
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perror("error writing buf1");
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return EXIT_FAILURE;
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}
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if (lseek(fd, BIGNUM, SEEK_CUR) == -1) {
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perror("lseek error");
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return EXIT_FAILURE;
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}
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if (write(fd, buf2, strlen(buf2)) != sizeof(buf2) - 1) {
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perror("error writing buf2");
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return EXIT_FAILURE;
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}
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sleep(30);
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(void)close(fd);
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return EXIT_SUCCESS;
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}
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