127 lines
2.8 KiB
C
127 lines
2.8 KiB
C
|
/* This file is part of the sample code and exercises
|
||
|
|
* used by the class "Advanced Programming in the UNIX
|
||
|
|
* Environment" taught by Jan Schaumann
|
||
|
|
* <jschauma@netmeister.org> at Stevens Institute of
|
||
|
|
* Technology.
|
||
|
|
*
|
||
|
|
* This file is in the public domain.
|
||
|
|
*
|
||
|
|
* You don't have to, but if you feel like
|
||
|
|
* acknowledging where you got this code, you may
|
||
|
|
* reference me by name, email address, or point
|
||
|
|
* people to the course website:
|
||
|
|
* https://stevens.netmeister.org/631/
|
||
|
|
*/
|
||
|
|
|
||
|
|
/* This simple program is used to illustrate that the OS does not free up
|
||
|
|
* the disk space used by a file immediately after a call to unlink(2),
|
||
|
|
* but only after the last process with an open handle has terminated.
|
||
|
|
*
|
||
|
|
* Run like this:
|
||
|
|
*
|
||
|
|
* $ cc -Wall wait-unlink.c
|
||
|
|
* $ ./a.out
|
||
|
|
*/
|
||
|
|
#include <fcntl.h>
|
||
|
|
#include <stdio.h>
|
||
|
|
#include <stdlib.h>
|
||
|
|
#include <unistd.h>
|
||
|
|
|
||
|
|
void
|
||
|
|
runDf() {
|
||
|
|
printf("\nAvailable space is now:\n");
|
||
|
|
if (system("df .") != 0) {
|
||
|
|
perror("unable to run df(1)");
|
||
|
|
exit(EXIT_FAILURE);
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
int
|
||
|
|
main() {
|
||
|
|
int fd;
|
||
|
|
|
||
|
|
/* "/tmp" is a memory file system on our
|
||
|
|
* reference platform, so let's use a separate
|
||
|
|
* temporary directory backed by a "normal"
|
||
|
|
* filesystem. */
|
||
|
|
if (chdir("/var/tmp") == -1) {
|
||
|
|
perror("unable to cd to /var/tmp");
|
||
|
|
exit(EXIT_FAILURE);
|
||
|
|
}
|
||
|
|
|
||
|
|
runDf();
|
||
|
|
|
||
|
|
/* Hit return to continue. */
|
||
|
|
(void)getchar();
|
||
|
|
|
||
|
|
printf("Creating a 500M file...\n");
|
||
|
|
if (system("dd if=/dev/zero of=foo bs=1024k count=500 >/dev/null") != 0) {
|
||
|
|
perror("unable to dd a new file");
|
||
|
|
exit(EXIT_FAILURE);
|
||
|
|
}
|
||
|
|
|
||
|
|
runDf();
|
||
|
|
|
||
|
|
(void)getchar();
|
||
|
|
printf("\nLinking 'bar' to 'foo'...\n\n");
|
||
|
|
if (link("foo", "bar") == -1) {
|
||
|
|
perror("unable to create a second hard link");
|
||
|
|
exit(EXIT_FAILURE);
|
||
|
|
}
|
||
|
|
|
||
|
|
if (system("ls -li foo bar") != 0) {
|
||
|
|
perror("unable to run ls(1)");
|
||
|
|
exit(EXIT_FAILURE);
|
||
|
|
}
|
||
|
|
|
||
|
|
runDf();
|
||
|
|
|
||
|
|
(void)getchar();
|
||
|
|
if ((fd = open("foo", O_RDWR)) < 0) {
|
||
|
|
perror("can't open file");
|
||
|
|
exit(EXIT_FAILURE);
|
||
|
|
}
|
||
|
|
printf("\nOpened 'foo' on fd#%d.\n", fd);
|
||
|
|
|
||
|
|
(void)getchar();
|
||
|
|
if (unlink("foo") < 0) {
|
||
|
|
perror("error unlinking");
|
||
|
|
exit(EXIT_FAILURE);
|
||
|
|
}
|
||
|
|
|
||
|
|
printf("\nOk, foo unlinked.\n");
|
||
|
|
printf("Disk space not free'd since 'bar' still exists...\n");
|
||
|
|
/* We expect system(3) to fail here, since 'foo' no longer exists. */
|
||
|
|
(void)system("ls -li foo bar");
|
||
|
|
|
||
|
|
runDf();
|
||
|
|
|
||
|
|
(void)getchar();
|
||
|
|
printf("\nOk, now unlinking 'bar'...\n");
|
||
|
|
if (unlink("bar") < 0) {
|
||
|
|
perror("error unlinking");
|
||
|
|
exit(EXIT_FAILURE);
|
||
|
|
}
|
||
|
|
|
||
|
|
printf("\nOk, bar unlinked.\n");
|
||
|
|
(void)getchar();
|
||
|
|
|
||
|
|
printf("Disk space not free'd since I still have fd#%d open...\n", fd);
|
||
|
|
printf("\nRunning 'ls -li foo bar':\n");
|
||
|
|
(void)system("ls -li foo bar");
|
||
|
|
|
||
|
|
runDf();
|
||
|
|
|
||
|
|
(void)getchar();
|
||
|
|
printf("Now closing fd#%d...\n", fd);
|
||
|
|
/* Closing the file descriptor after having
|
||
|
|
* unlinked all references to the 500M file
|
||
|
|
* finally frees the disk space. */
|
||
|
|
(void)close(fd);
|
||
|
|
printf("\n...and done. Disk space is freed now.\n");
|
||
|
|
|
||
|
|
runDf();
|
||
|
|
|
||
|
|
exit(EXIT_SUCCESS);
|
||
|
|
}
|