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| -rw-r--r-- | man2/kcmp.2 | 108 |
1 files changed, 107 insertions, 1 deletions
diff --git a/man2/kcmp.2 b/man2/kcmp.2 index 3a5a879edd..57a0bb21d3 100644 --- a/man2/kcmp.2 +++ b/man2/kcmp.2 @@ -1,5 +1,5 @@ .\" Copyright (C) 2012, Cyrill Gorcunov <gorcunov@openvz.org> -.\" and Copyright (C) 2012, Michael Kerrisk <mtk.manpages@gmail.com> +.\" and Copyright (C) 2012, 2016, Michael Kerrisk <mtk.manpages@gmail.com> .\" .\" %%%LICENSE_START(VERBATIM) .\" Permission is granted to make and distribute verbatim copies of this @@ -239,6 +239,112 @@ See .BR clone (2) for some background information on the shared resources referred to on this page. +.SH EXAMPLE +The program below uses +.BR kcmp () +to test whether pairs of file descriptors refer to +the same open file description. +The program tests different cases for the file descriptor pairs, +as described in the program output. +An example run of the program is as follows: + +.nf +.in +4n +$ \fB./a.out\fP +Parent PID is 1144 +Parent opened file on FD 3 + +PID of child of fork() is 1145 + Compare duplicate FDs from different processes: + kcmp(1145, 1144, KCMP_FILE, 3, 3) ==> same +Child opened file on FD 4 + Compare FDs from distinct open()s in same process: + kcmp(1145, 1145, KCMP_FILE, 3, 4) ==> different +Child duplicated FD 3 to create FD 5 + Compare duplicated FDs in same process: + kcmp(1145, 1145, KCMP_FILE, 3, 5) ==> same +.in +.fi +.SS Program source +\& +.nf +#define _GNU_SOURCE +#include <sys/syscall.h> +#include <sys/wait.h> +#include <sys/stat.h> +#include <stdlib.h> +#include <stdio.h> +#include <unistd.h> +#include <fcntl.h> +#include <linux/kcmp.h> + +#define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); \\ + } while (0) + +static int +kcmp(pid_t pid1, pid_t pid2, int type, + unsigned long idx1, unsigned long idx2) +{ + return syscall(SYS_kcmp, pid1, pid2, type, idx1, idx2); +} + +static void +test_kcmp(char *msg, id_t pid1, pid_t pid2, int fd_a, int fd_b) +{ + printf("\\t%s\\n", msg); + printf("\\t\\tkcmp(%ld, %ld, KCMP_FILE, %d, %d) ==> %s\\n", + (long) pid1, (long) pid2, fd_a, fd_b, + (kcmp(pid1, pid2, KCMP_FILE, fd_a, fd_b) == 0) ? + "same" : "different"); +} + +int +main(int argc, char *argv[]) +{ + int fd1, fd2, fd3; + char pathname[] = "/tmp/kcmp.test"; + + fd1 = open(pathname, O_CREAT | O_RDWR, S_IRUSR | S_IWUSR); + if (fd1 == \-1) + errExit("open"); + + printf("Parent PID is %ld\\n", (long) getpid()); + printf("Parent opened file on FD %d\\n\\n", fd1); + + switch (fork()) { + case \-1: + errExit("fork"); + + case 0: + printf("PID of child of fork() is %ld\\n", (long) getpid()); + + test_kcmp("Compare duplicate FDs from different processes:", + getpid(), getppid(), fd1, fd1); + + fd2 = open(pathname, O_CREAT | O_RDWR, S_IRUSR | S_IWUSR); + if (fd2 == \-1) + errExit("open"); + printf("Child opened file on FD %d\\n", fd2); + + test_kcmp("Compare FDs from distinct open()s in same process:", + getpid(), getpid(), fd1, fd2); + + fd3 = dup(fd1); + if (fd3 == \-1) + errExit("dup"); + printf("Child duplicated FD %d to create FD %d\\n", fd1, fd3); + + test_kcmp("Compare duplicated FDs in same process:", + getpid(), getpid(), fd1, fd3); + break; + + default: + wait(NULL); + } + + exit(EXIT_SUCCESS); +} +.fi .SH SEE ALSO .BR clone (2), .BR unshare (2) |