From b9224fe08d3541fa93933b555619479a68be7ba1 Mon Sep 17 00:00:00 2001
From: Santo Cariotti <santo@dcariotti.me>
Date: Sun, 26 Sep 2021 12:34:22 +0200
Subject: os: add exercise 2021-07-26

---
 Year_2/OS/my-dus-c.c | 204 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 204 insertions(+)
 create mode 100644 Year_2/OS/my-dus-c.c

diff --git a/Year_2/OS/my-dus-c.c b/Year_2/OS/my-dus-c.c
new file mode 100644
index 0000000..5961c77
--- /dev/null
+++ b/Year_2/OS/my-dus-c.c
@@ -0,0 +1,204 @@
+/*
+ * Test the equivalent execution of this propgram with `du`:
+ *
+ * du --block-size=512 -s <path>
+ *
+ */
+#include <dirent.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ipc.h>
+#include <sys/sem.h>
+#include <sys/shm.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#define MAX_PATH_LEN 1024
+
+int
+WAIT(int id_sem, int n)
+{
+    struct sembuf sops[1] = { { n, -1, 0 } };
+
+    return semop(id_sem, sops, 1);
+}
+
+int
+SIGNAL(int id_sem, int n)
+{
+    struct sembuf sops[1] = { { n, 1, 0 } };
+
+    return semop(id_sem, sops, 1);
+}
+
+void
+handle_scanner_end(int id_shm, int id_sem, int id_scanner, char* pathname)
+{
+    char* msg;
+
+    if ((msg = (char*)shmat(id_shm, NULL, 0)) == (char*)-1) {
+        perror("shmat");
+        exit(1);
+    }
+
+    WAIT(id_sem, 0);
+    sprintf(msg, "%d;END;%s", id_scanner, pathname);
+    SIGNAL(id_sem, 1);
+}
+
+void
+stater(int id_shm, int id_sem, int* scanners, int scanners_n)
+{
+    char* msg;
+    int n;
+    struct stat sb;
+    char* token;
+    char* pathname;
+    int sid;
+
+    if ((msg = (char*)shmat(id_shm, NULL, 0)) == (char*)-1) {
+        perror("shmat");
+        exit(1);
+    }
+
+    n = 0;
+    while (n < scanners_n) {
+        WAIT(id_sem, 1);
+        /* I previously opened the file with `open` so I know I can read
+             * that. So now I open that file with stat, because `msg` contains
+             * the patname as string.
+             * But first I have to parse the `msg` receiving the scanner id.
+             */
+        token = strtok(msg, ";");
+        sid = atoi(token);
+        pathname = strtok(NULL, ";");
+
+        if (strcmp(pathname, "END") == 0) {
+            pathname = strtok(NULL, ";");
+            printf("%d\t%s\n", scanners[sid], pathname);
+            n++;
+        } else {
+            stat(pathname, &sb);
+            scanners[sid] += sb.st_blocks;
+        }
+        SIGNAL(id_sem, 0);
+    }
+}
+
+void
+scanner(int id_shm, int id_sem, int scanner_id, char* pathname)
+{
+    char* msg;
+    struct stat sb;
+    struct dirent* db;
+    int fd;
+    DIR* dp;
+    char buffer[MAX_PATH_LEN];
+
+    if ((msg = (char*)shmat(id_shm, NULL, 0)) == (char*)-1) {
+        perror("shmat");
+        exit(1);
+    }
+
+    if ((fd = open(pathname, O_RDONLY)) == -1) {
+        perror("open");
+        exit(1);
+    }
+
+    fstat(fd, &sb);
+
+    if ((sb.st_mode & S_IFMT) == S_IFDIR) {
+        if ((dp = opendir(pathname)) == NULL) {
+            perror("opendir");
+            exit(1);
+        }
+
+        while ((db = readdir(dp)) != NULL) {
+            if ((strcmp(db->d_name, ".") == 0) || strcmp(db->d_name, "..") == 0)
+                continue;
+            sprintf(buffer, "%s/%s", pathname, db->d_name);
+            scanner(id_shm, id_sem, scanner_id, buffer);
+        }
+
+        closedir(dp);
+    }
+
+    WAIT(id_sem, 0);
+    sprintf(msg, "%d;%s", scanner_id, pathname);
+    SIGNAL(id_sem, 1);
+}
+
+int
+main(int argc, char* argv[])
+{
+    int id_shm;
+    int i;
+    pid_t pid;
+    pid_t pid_scanners[argc - 1];
+    int scanners[argc - 1];
+    int id_sem;
+
+    for (i = 0; i < argc - 1; ++i)
+        scanners[i] = 0;
+
+    if ((id_shm = shmget(IPC_PRIVATE, 1024, IPC_CREAT | IPC_EXCL | 0644)) == -1) {
+        perror("shmget");
+        exit(1);
+    }
+
+    if ((id_sem = semget(IPC_PRIVATE, 2, IPC_CREAT | IPC_EXCL | 0644)) == -1) {
+        perror("semget");
+        exit(1);
+    }
+
+    semctl(id_sem, 0, SETVAL, 1);
+    semctl(id_sem, 1, SETVAL, 0);
+
+    if (argc < 2) {
+        exit(0);
+    }
+
+    pid = fork();
+    if (pid == -1) {
+        perror("fork");
+        exit(1);
+    }
+
+    if (pid == 0) {
+        stater(id_shm, id_sem, scanners, argc - 1);
+        exit(0);
+    }
+
+    for (i = 1; i < argc; ++i) {
+        pid_scanners[i - 1] = fork();
+        if (pid_scanners[i - 1] == -1) {
+            perror("fork");
+            exit(1);
+        }
+
+        if (pid_scanners[i - 1] == 0) {
+            scanner(id_shm, id_sem, i - 1, argv[i]);
+            handle_scanner_end(id_shm, id_sem, i - 1, argv[i]);
+            exit(0);
+        }
+    }
+
+    for (i = 0; i < argc; ++i)
+        wait(NULL);
+
+    if (shmctl(id_shm, IPC_RMID, NULL) == -1) {
+        perror("shmctl");
+        exit(1);
+    }
+
+    if (semctl(id_sem, 2, IPC_RMID) == -1) {
+        perror("semctl");
+        exit(1);
+    }
+
+    return 0;
+}
-- 
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