feat(lab2): unix lab2 done

Lab 2 is in fact the first lab in the set of ones we actually do. It's
not particularly hard, but consumed some time for me

OSs/lab2/unix/part-A/father.c

@@ -0,0 +1,56 @@
+/*
+ * "THE CHEESE-WARE LICENSE" (Revision 1):
+ * <ElectronixTM> wrote this file. As long as you retain this notice
+ * you can do whatever you want with this stuff. If we meet some day,
+ * and you think this stuff is worth it, you can buy me some cheese
+ * in return
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/wait.h>
+#include <assert.h>
+
+#include "common.h"
+
+#define PROG_PREFIX "father: "
+#define log(fmt, args...) printf(PROG_PREFIX fmt "\n", ##args)
+
+#define CMD_SIZE 256
+
+int main(int argc, const char **argv)
+{
+    if (argc != 2) {
+        log("Wrong program usage. 1 argument shuld be passed - program mode");
+        log("%d - wait for child", WAIT_FOR_CHILD);
+        log("%d - father doesn't wait for child", DONT_WAIT_FOR_CHILD);
+        log("%d - father doesn't wait for child, but child finishes",
+             ZOMBIE_PROCESS);
+        return EXIT_FAILURE;
+    }
+    long mode = strtol(argv[1], NULL, 10);
+    if (fork() == 0) {
+        execl("son", "son", argv[1], NULL);
+    }
+    char cmd[CMD_SIZE] = {0};
+    snprintf(cmd, CMD_SIZE, "ps fx > task_dump-%ld", mode);
+    if (mode == WAIT_FOR_CHILD) {
+        system(cmd);
+        int status = 0;
+        int ret = wait(&status);
+        if (ret < 0) {
+            log("waiting for son ended with error code %d", ret);
+            return EXIT_FAILURE;
+        }
+    } else if (mode == DONT_WAIT_FOR_CHILD) {
+        system(cmd);
+    } else if (mode == ZOMBIE_PROCESS) {
+        sleep(2);
+        system(cmd);
+    } else {
+        log("Invalid argument. No mode correspoiding to %ld", mode);
+        return EXIT_FAILURE;
+    }
+    return EXIT_SUCCESS;
+}