From 6834a4c4094d133e771491b134e8da73a9f00a07 Mon Sep 17 00:00:00 2001
From: Paul Buetow <paul@buetow.org>
Date: Mon, 24 Mar 2025 21:37:10 +0200
Subject: add mini fork test tool

---
 tools/forktest.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)
 create mode 100644 tools/forktest.c

(limited to 'tools/forktest.c')

diff --git a/tools/forktest.c b/tools/forktest.c
new file mode 100644
index 0000000..49dc40e
--- /dev/null
+++ b/tools/forktest.c
@@ -0,0 +1,46 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+
+int main() {
+    int fd = open("testfile", O_WRONLY| O_CREAT, 0644);
+    if (fd < 0) {
+        perror("open");
+        return 1;
+    }
+    int flags = fcntl(fd, F_GETFL);
+    printf("Parent: File access mode is O_RDWR|O_CREAT (%d %d %d)\n", flags, O_RDWR|O_CREAT, O_WRONLY|O_CREAT);
+
+    pid_t pid = fork();
+    if (pid < 0) {
+        perror("fork");
+        return 1;
+    } else if (pid == 0) { // Child process
+        // Change file access mode
+        if (fcntl(fd, F_SETFL, O_RDONLY) < 0) {
+            perror("fcntl");
+            return 1;
+        }
+        int flags = fcntl(fd, F_GETFL);
+        printf("Child: Changed file access mode to O_RDONLY|.. (%d)\n", flags);
+        _exit(0);
+    } else { // Parent process
+        sleep(2);
+        int flags = fcntl(fd, F_GETFL);
+        if (flags < 0) {
+            perror("fcntl");
+            return 1;
+        }
+        if (flags & O_RDONLY) {
+            printf("Parent: File access mode changed to O_RDONLY|.. (%d)\n", flags);
+        } else {
+            printf("Parent: File access mode is still O_RDWR|.. (%d)\n", flags);
+        }
+    }
+
+    close(fd);
+    return 0;
+}
-- 
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