Public bug reported:
Release: Ubuntu 16.04.2 LTS
Package: libc6:
Installed: 2.23-0ubuntu7
The ftok man page states that: "The resulting value is the same for all
pathnames that name the same file, when the same value of proj_id is
used".
However, if you call ftok() twice with the same path and id, and the
file has been deleted and created again in between (and the inode of the
file has been changed by this operation, which it will if other files
were created in between), then the result of ftok() will not be the
same.
The following program can be used to reproduce the issue:
#include <sys/types.h>
#include <sys/ipc.h>
#include <stdio.h>
#include <unistd.h>
int main(int argc, char **argv)
{
int id = 121;
if (argc != 2) {
printf("Usage: ft <file>\n");
return 1;
}
if (access(argv[1], F_OK) < 0) {
printf("Failed to access file\n");
return 1;
}
printf("ftok %s %d: 0x%x\n", argv[1], id, ftok(argv[1], (char)id));
return 0;
}
Compile it into a binary named 'ft', then do the following:
$ touch foo
$ ./ft foo
ftok foo 121: 0x790225bd
$ rm foo
$ touch bar
$ touch foo
$ ftok foo
ftok foo 121: 0x790226ea
The result is not the same although the path and id are the same, which
is not what should happen according to the man page.
** Affects: glibc (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1767097
Title:
ftok() returns different result for same (path, id) pair if the inode
of the file is changed
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