Fix wrong argument of write. Fix return type of getdents. Fix procfs_getdents. Finish implementing the base version of the ps command.

programs/ps.c

@@ -7,21 +7,19 @@
 #include <sys/stat.h>
 #include <fcntl.h>
 #include <stdio.h>
-#include <strerror.h>
 #include <string.h>
+#include <stdlib.h>
 
 #define FORMAT_S "%5s %5s %6s %s\n"
 #define FORMAT   "%5d %5d %6c %s\n"
 
-static inline void __iterate_proc_dirs(int fd)
+static inline void __iterate_proc_dirs(int proc_fd)
 {
     char absolute_path[PATH_MAX] = "/proc/";
     // Holds the file descriptor of the stat file.
     int stat_fd;
     // Buffer used to read the stat file.
     char stat_buffer[BUFSIZ] = { 0 };
-    // Holds the number of bytes read from stat file.
-    ssize_t ret;
     // Variables used to read the stat file.
     // (1) pid   %d
     // (2) comm  %s
@@ -33,7 +31,20 @@ static inline void __iterate_proc_dirs(int fd)
     pid_t ppid;
     // The directory entry.
     dirent_t dent;
-    while (getdents(fd, &dent, sizeof(dirent_t)) == sizeof(dirent_t)) {
+    // Holds the number of bytes read.
+    ssize_t read_bytes;
+    do {
+        // Read an entry.
+        read_bytes = getdents(proc_fd, &dent, sizeof(dirent_t));
+        // We reached the end of the folder.
+        if (read_bytes == 0) {
+            break;
+        }
+        // We encountered an error.
+        if (read_bytes == -1) {
+            perror("Failed to read entry in `/proc` folder");
+            exit(EXIT_FAILURE);
+        }
         // Skip non-directories.
         if (dent.d_type != DT_DIR)
             continue;
@@ -42,14 +53,20 @@ static inline void __iterate_proc_dirs(int fd)
         strcat(absolute_path, "/stat");
         // Open the `/proc/<pid>/stat` file.
         if ((stat_fd = open(absolute_path, O_RDONLY, 0)) == -1) {
-            printf("Failed to open `%s`\n", absolute_path);
+            printf("Failed to open `%s`: ", absolute_path);
+            perror(NULL);
+            putchar('\n');
             continue;
         }
         // Reset the stat buffer.
         memset(stat_buffer, 0, BUFSIZ);
         // Read the content of the stat file.
-        if ((ret = read(stat_fd, stat_buffer, BUFSIZ)) <= 0) {
-            printf("Cannot read `%s`\n", absolute_path);
+        read_bytes = read(stat_fd, stat_buffer, BUFSIZ);
+        // Check if the read failed.
+        if (read_bytes <= 0) {
+            printf("Cannot read `%s`", absolute_path);
+            perror(NULL);
+            putchar('\n');
             close(stat_fd);
             continue;
         }
@@ -61,14 +78,15 @@ static inline void __iterate_proc_dirs(int fd)
         printf(FORMAT, pid, ppid, state, comm);
         // Closing stat FD.
         close(stat_fd);
-    }
+    } while (1);
 }
 
 int main(int argc, char **argv)
 {
     int fd = open("/proc", O_RDONLY | O_DIRECTORY, 0);
     if (fd == -1) {
-        printf("ps: cannot access '/proc': %s\n\n", strerror(errno));
+        perror("ps: cannot access '/proc' folder");
+        return EXIT_FAILURE;
     } else {
         printf(FORMAT_S, "PID", "PPID", "STATUS", "CMD");
         __iterate_proc_dirs(fd);
@@ -124,5 +142,5 @@ int main(int argc, char **argv)
     }
     close(fd_self);
 #endif
-    return 0;
+    return EXIT_SUCCESS;
 }