implement dup syscall

programs/tests/CMakeLists.txt

@@ -1,5 +1,6 @@
 # List of programs.
 set(TEST_LIST
+    t_dup.c
     t_creat.c
     t_write_read.c
     t_gid.c

programs/tests/t_dup.c

@@ -0,0 +1,64 @@
+/// @file t_dup.c
+/// @brief Test the dup syscall
+/// @copyright (c) 2024 This file is distributed under the MIT License.
+/// See LICENSE.md for details.
+
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/unistd.h>
+#include <strerror.h>
+#include <string.h>
+
+int main(int argc, char *argv[])
+{
+    char *file        = "t_dup_file";
+    int fd1, fd2;
+    int flags = O_WRONLY | O_CREAT | O_TRUNC;
+    mode_t mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP;
+
+    fd1 = open(file, flags, mode);
+    if (fd1 < 0) {
+        printf("Failed to open file %s: %s\n", file, strerror(errno));
+        exit(1);
+    }
+
+    fd2 = dup(fd1);
+    if (fd2 < 0) {
+        printf("Failed to dup fd %d: %s\n", fd1, strerror(errno));
+        exit(1);
+    }
+
+    if (write(fd1, "foo", 3) != 3) {
+        printf("Writing to fd %d failed: %s\n", fd1, strerror(errno));
+        exit(1);
+    }
+    close(fd1);
+
+    if (write(fd2, "bar", 3) != 3) {
+        printf("Writing to fd %d failed: %s\n", fd2, strerror(errno));
+        exit(1);
+    }
+    close(fd2);
+
+    fd1 = open(file, O_RDONLY, 0);
+    if (fd1 < 0) {
+        printf("Failed to open file %s: %s\n", file, strerror(errno));
+        exit(1);
+    }
+
+    char buf[7];
+    buf[6] = 0;
+    if (read(fd1, &buf, 6) < 0) {
+        printf("Reading from fd %d failed: %s\n", fd1, strerror(errno));
+        exit(1);
+    }
+
+    if (strcmp(buf, "foobar") != 0) {
+        printf("Unexpected file content: %s\n", buf);
+        exit(1);
+    }
+
+    unlink(file);
+    return 0;
+}