@@ -97,6 +97,7 @@ TARGETS += sparc64
TARGETS += splice
TARGETS += static_keys
TARGETS += sync
+TARGETS += syscalls/fork_syscall
TARGETS += syscall_user_dispatch
TARGETS += sysctl
TARGETS += tc-testing
new file mode 100644
@@ -0,0 +1 @@
+// SPDX-License-Identifier: GPL-2.0
\ No newline at end of file
new file mode 100644
@@ -0,0 +1 @@
+# SPDX-License-Identifier: GPL-2.0-only
\ No newline at end of file
new file mode 100644
@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: GPL-2.0
+TEST_GEN_PROGS := fork_syscall
+CFLAGS += -Wall
+
+include ../lib.mk
\ No newline at end of file
new file mode 100644
@@ -0,0 +1,151 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/* kselftest for fork() system call
+ *
+ * Summery : fork() system call is used to create a new process
+ * by duplicating an existing one. The new process, known as the
+ * child process, is a copy of the parent process.
+ *
+ * Child process is dublicate process but has different PID and
+ * memory allocation.
+ *
+ * About the test : With this test we are testing the following:
+ * - Child PID which fork() returns to Parent is present in /proc
+ * - Child PID is not same as Parent PID.
+ * - Memory allocation to a variable in child and parent process
+ * is different.
+*/
+
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <dirent.h>
+#include <ctype.h>
+
+#include "../../kselftest.h"
+
+// Function to check if a string is numeric (PID check)
+int is_numeric(const char *str) {
+ while (*str) {
+ if (!isdigit(*str)) return 0;
+ str++;
+ }
+ return 1;
+}
+
+// Function to find the child PID in /proc
+pid_t find_child_pid(pid_t parent_pid) {
+ DIR *proc_dir = opendir("/proc");
+ struct dirent *entry;
+
+ if (proc_dir == NULL) {
+ perror("Failed to open /proc directory");
+ ksft_exit_fail();
+ return 1;
+ }
+
+ // Iterate through the /proc directory to find PIDs
+ while ((entry = readdir(proc_dir)) != NULL) {
+ // Check if the entry is a PID
+ if (is_numeric(entry->d_name)) {
+ pid_t pid = atoi(entry->d_name);
+
+ // Construct the path to /proc/<pid>/
+ //stat to check the parent PID
+
+ char path[40], buffer[100];
+ snprintf(path, 40, "/proc/%d/stat", pid);
+
+ FILE *stat_file = fopen(path, "r");
+ if (stat_file != NULL) {
+ fgets(buffer, 100, stat_file);
+ fclose(stat_file);
+
+ // The fourth field in /proc/<pid>/stat is the parent PID
+ pid_t ppid;
+ sscanf(buffer, "%*d %*s %*c %d", &ppid);
+
+ if (ppid == parent_pid) {
+ closedir(proc_dir);
+ // Return the child PID if the parent PID matches
+ return pid;
+ }
+ }
+ }
+ }
+
+ closedir(proc_dir);
+
+ // Return -1 if no child PID was found
+ return -1;
+}
+
+int main(void) {
+
+ // Setting up kselftest framework
+ ksft_print_header();
+ ksft_set_plan(1);
+
+ // Check if test is run a root
+ if (geteuid()) {
+ ksft_test_result_skip("This test needs root to run!\n");
+ return 1;
+ }
+
+ // forking
+ pid_t pid = fork();
+
+ // Declare a variable in both parent and child processes
+ int var = 17;
+
+ if (pid == -1) {
+ ksft_test_result_error("%s.\n", strerror(errno));
+ ksft_finished();
+ return 1;
+
+ } else if (pid == 0) {
+ // This is the child process
+ ksft_print_msg("Inside the child process.\n");
+ var = 1998;
+
+ } else {
+ // This is the parent process
+ pid_t ppid=getpid();
+ ksft_print_msg("Inside the parent process.\n");
+ ksft_print_msg("Child PID got from fork() return : %d\n", pid);
+ ksft_print_msg("Parent PID from getpid(): %d\n",ppid);
+
+ // Find the child PID in /proc
+ pid_t child_pid = find_child_pid(getpid());
+ if (child_pid != -1) {
+ ksft_set_plan(2);
+ if(child_pid == pid && pid != ppid && var != 1998) {
+ ksft_test_result_pass("Child Pid from /proc and fork() matching\n");
+ ksft_test_result_pass("Child Pid != Parent pid\n");
+ ksft_set_plan(3);
+ ksft_test_result_pass(
+ "After modification in child No effect on the value of 'var' in parent\n");
+ ksft_exit_pass();
+ return 0;
+ }
+ else {
+ ksft_exit_fail();
+ return 1;
+ }
+ }
+ else {
+ ksft_test_result_fail("Child Pid from /proc and fork() does not match");
+ ksft_exit_fail();
+ return 1;
+ }
+
+ // Wait for the child process to finish
+ wait(NULL);
+ }
+
+ return 0;
+}
+
This test verifies the correct behavior of the fork() system call, which creates a child process by duplicating the parent process. The test checks the following: - The child PID returned by fork() is present in /proc. - The child PID is different from the parent PID. - The memory allocated to a variable in the child process is independent of the parent process. Test logs : - Run without root TAP version 13 1..1 ok 1 # SKIP This test needs root to run! - Run with root TAP version 13 1..1 # Inside the parent process. # Child PID got from fork() return : 56038 # Parent PID from getpid(): 56037 # Inside the child process. 1..2 ok 1 Child Pid from /proc and fork() matching ok 2 Child Pid != Parent pid 1..3 ok 3 After modification in child No effect on the value of 'var' in parent # Totals: pass:3 fail:0 xfail:0 xpass:0 skip:0 error:0 Signed-off-by: Shivam Chaudhary <cvam0000@gmail.com> --- Here is my proposal for a new directory, /syscalls, to add syscall selftests, as there is currently no dedicated space for these tests. I encountered this issue while writing the test case for the delete_module syscall and was unsure where to place it. As a heads-up, the delete_module test is currently under review, and I would like to add it to this directory. tools/testing/selftests/Makefile | 1 + tools/testing/selftests/syscalls/.gitignore | 1 + .../syscalls/fork_syscall/.gitignore | 1 + .../selftests/syscalls/fork_syscall/Makefile | 5 + .../syscalls/fork_syscall/fork_syscall.c | 151 ++++++++++++++++++ 5 files changed, 159 insertions(+) create mode 100644 tools/testing/selftests/syscalls/.gitignore create mode 100644 tools/testing/selftests/syscalls/fork_syscall/.gitignore create mode 100644 tools/testing/selftests/syscalls/fork_syscall/Makefile create mode 100644 tools/testing/selftests/syscalls/fork_syscall/fork_syscall.c