From efaec4509af562d79582dad8017334d778489aaa Mon Sep 17 00:00:00 2001
From: Santo Cariotti <santo@dcariotti.me>
Date: Thu, 16 Sep 2021 23:42:55 +0200
Subject: os: add homework 7

---
 Year_2/OS/hw/hw7.c | 156 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 156 insertions(+)
 create mode 100644 Year_2/OS/hw/hw7.c

(limited to 'Year_2/OS/hw/hw7.c')

diff --git a/Year_2/OS/hw/hw7.c b/Year_2/OS/hw/hw7.c
new file mode 100644
index 0000000..ca51998
--- /dev/null
+++ b/Year_2/OS/hw/hw7.c
@@ -0,0 +1,156 @@
+/*
+    Homework n.7
+
+    Modificare l'homework precedente (n.6) facendo in modo che il figlio che
+    riceve il comando da eseguire tramite la coda, catturi lo standard output
+    e lo standard error del figlio nipote usando la redirezione su pipe tra
+    processi. L'output catturato dovrà essere mandato indietro al padre
+    tramite un messaggio (per semplicita', assumiamo sufficiente grande).
+    Tale contenuto sara' poi visualizzato sul terminale dal padre.
+
+*/
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ipc.h>
+#include <sys/msg.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#define MTYPE 1
+#define MTYPE_EXE 2
+
+struct msgbuf {
+    long mtype;
+    char mtext[1024];
+};
+
+void
+execute(int qid)
+{
+    pid_t pid;
+    struct msgbuf msg;
+    char command[1024];
+    int n;
+    char* p;
+    int pipefd[2];
+
+    while (1) {
+        if (msgrcv(qid, (void*)&msg, 1024, MTYPE, 0) == -1) {
+            perror("msgrcv");
+            exit(1);
+        }
+
+        /* The variable `command` will be the substring of the passed string
+         * until the first space, ignoring all parameters */
+        n = 0;
+        p = msg.mtext;
+        while (*p != '\0') {
+            if (*p == ' ')
+                break;
+            n++;
+            p++;
+        }
+
+        strncpy(command, msg.mtext, n);
+        command[n] = '\0';
+
+        if (strcmp(command, "exit") == 0)
+            break;
+
+        if (pipe(pipefd) == -1) {
+            perror("pipe");
+            exit(1);
+        }
+
+        pid = fork();
+        if (pid == -1) {
+            perror("fork");
+            exit(1);
+        }
+
+        if (pid == 0) {
+            dup2(pipefd[1], 1);
+            dup2(pipefd[1], 2);
+            close(pipefd[0]);
+            execlp(command, "", NULL);
+            fprintf(stderr, "Error executing '%s'\n", command);
+            exit(1);
+        } else {
+            wait(NULL);
+
+            close(pipefd[1]);
+            n = read(pipefd[0], msg.mtext, 1024);
+            msg.mtext[n] = '\0';
+            msg.mtype = MTYPE_EXE;
+            close(pipefd[0]);
+
+            if (msgsnd(qid, (void*)&msg, strlen(msg.mtext) + 1, 0) == -1) {
+                perror("msgsnd");
+                exit(1);
+            }
+        }
+    }
+
+    msgctl(qid, IPC_RMID, NULL);
+}
+
+int
+main()
+{
+    pid_t pid;
+    int qid;
+    int n;
+
+    if ((qid = msgget(IPC_PRIVATE, IPC_CREAT | 0644)) == -1) {
+        perror("msgget");
+        exit(1);
+    }
+
+    pid = fork();
+    if (pid == -1) {
+        perror("fork");
+        exit(1);
+    }
+
+    if (pid != 0) {
+        struct msgbuf msg;
+        while (1) {
+            printf("Insert a command: ");
+            fgets(msg.mtext, 1024, stdin);
+            n = strlen(msg.mtext);
+            msg.mtext[n - 1] = '\0';
+            msg.mtype = MTYPE;
+
+            /* Ignore empty string */
+            if (strcmp(msg.mtext, "") == 0)
+                continue;
+
+            if (msgsnd(qid, (void*)&msg, sizeof(msg.mtext), IPC_NOWAIT) == -1) {
+                perror("msgsnd");
+                exit(1);
+            }
+
+            /* Check first if the message is exit, because executing this when
+             * message is "exit" raises 
+             * msgrcv: Identifier removed
+             */
+            if (strcmp(msg.mtext, "exit") == 0) {
+                break;
+            }
+
+            if (msgrcv(qid, (void*)&msg, 1024, MTYPE_EXE, 0) == -1) {
+                perror("msgrcv");
+                exit(1);
+            }
+
+            printf("%s\n", msg.mtext);
+            sleep(1);
+        }
+    } else {
+        execute(qid);
+    }
+
+    return 0;
+}
-- 
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