Fixed child process bug and updated documentation

.github/workflows/wolf.yml

@@ -0,0 +1,14 @@
+name: wolf
+on:
+  push:
+    branches: [master]
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Build Wolf
+        run: |
+          make clean build

Makefile

@@ -8,7 +8,7 @@ DEBUG_CFLAGS = -Wall -Wextra -Werror -pedantic-errors -fstack-protector-strong \
 		 -Wwrite-strings -std=c99 -g
 CFLAGS = -Wall -Wextra -Werror -pedantic-errors -Wwrite-strings -std=c99 -O3
 
-BUILD_FLAGS = -DVERSION=\"0.0.2\"
+BUILD_FLAGS = -DVERSION=\"0.0.3\"
 
 build: $(TARGET)
 debug: $(DEBUG_TARGET)

README.md

@@ -1,4 +1,4 @@
-# Wolf 🐺
+# Wolf 🐺 [![](https://github.com/ceticamarco/wolf/actions/workflows/wolf.yml/badge.svg)](https://github.com/ceticamarco/wolf/actions/workflows/wolf.yml)
 
 **Wolf** is a configurable file watchdog for Linux platform written in C. **Wolf** monitors 
 a set of files or directories and prints out a log event each time the watched resources changes. The watchdog
@@ -34,7 +34,7 @@ options:
 -v, --version             | Show program version
 -h, --help                | Show this helper
 
-General help with the software: https://git.marcocetica.com/marco/wolf
+Project homepage: https://github.com/ceticamarco/wolf
 Report bugs to: Marco Cetica(<email@marcocetica.com>)
 ```
 
@@ -103,7 +103,8 @@ P '/home/marco/wolf/a.out' (file)
 W '/home/marco/wolf/a.out' (file)
 ```
 Additionally, if you want to execute a custom command every time a watchdog detects a change, you can do so by
-using the `-e,--exec` option. For instance, suppose that you have a Python file(`foo.py`) with the following content:
+using the `-e,--exec` option. For instance, suppose that you have a Python file(`foo.py`) on the current directory 
+with the following content:
 
 ```py
 def square(x):
@@ -116,14 +117,14 @@ and you want to continously evaluate it as soon as you save it to the disk. To d
 below:
 
 ```sh
-$> ./wolf -w --exec 'python foo.py'
+$> ./wolf -w --exec 'python foo.py' .
 ```
 
 Each time a write event is detected by the watchdog, the supplied command will be issued, causing the program 
 to be automatically evaluated, that is:
 
 ```sh
-$> ./wolf -w --exec 'python foo.py'
+$> ./wolf -w --exec 'python foo.py' .
 [2024-08-20 16:24:43] W 'foo.py' (file)
 10^2 = 100
 [2024-08-20 16:24:55] W 'foo.py' (file)
@@ -143,11 +144,9 @@ Below there is a brief list of the things you should be aware of when using **Wo
 
 - The `-e,--exec` option works by spawning a child process using the `fork(2)` system call; thus, the command is being executed
 in a new process;  
-- The `-e,--exec` option is a **NON-BLOCKING** feature, meaning that the parent process will continue to log new changes while the
-child process execute the supplied command; therefore the parent process will **NOT** wait for the child(s) process to terminate;  
-- Since the parent process does not await for the child process to complete it will also not handle its return code, thus the exit
-status of any supplied command is ignored.
-- Any `SIGCHLD` signal generated by a child process is ignored, therefore the reaping of any child process is delegated to the kernel;  
+- The `-e,--exec` option is a **BLOCKING** feature, meaning that the parent process waits for the child process to terminate
+before logging new changes;  
+- The child's return code will be printed to standard output only if it is non-zero or if the child was terminated by a signal;  
 - `inotify` is **NOT** recursive. Meaning that you cannot monitor subdirectories of a watched directory;  
 - `inotify` can only work within files for which you already have reading and writing permissions;  
 - `inotify` removes deleted files from the `inotify_add_watch(2)`, meaning that, after a file is being deleted, the watchdog associated with it 

wolf.c

@@ -61,13 +61,13 @@ void helper(const char *name) {
            "--no-timestamp            | Disable timestamp from watchdog output\n"
            "-v, --version             | Show program version\n"
            "-h, --help                | Show this helper\n\n"
-           "General help with the software: https://git.marcocetica.com/marco/wolf\n"
+           "Project homepage: https://github.com/ceticamarco/wolf\n"
            "Report bugs to: Marco Cetica(<email@marcocetica.com>)\n", name);
 }
 
 void version() {
     printf("Wolf (v%s) - Configurable file watchdog for Linux platform.\n"
-           "Copyright (c) 2024 Marco Cetica\n"
+           "Copyright (c) 2024, 2025 Marco Cetica\n"
            "License GPLv3+: GNU GPL version 3 or later\n\n"
            "Project homepage: <https://git.marcocetica.com/marco/wolf>.\n"
            "Email bug reports to: <email@marcocetica.com>.\n", VERSION);
@@ -300,13 +300,6 @@ static void get_timestamp(uint8_t *timestamp, const ssize_t timestamp_len) {
 }
 
 static void exec_command(const char *cmd) {
-    // Ignore SIGCHLD signals.
-    // This allows us to avoid blocking the parent process until the child completes
-    // its execution; furthermore, it allows us to prevent the creation of zombie processes
-    // by delegating the cleanup process to the kernel. By doing so, we lose the ability 
-    // to check the return status of the child process.
-    signal(SIGCHLD, SIG_IGN);
-
     // Execute command in a new process
     pid_t pid = fork();
     
@@ -333,6 +326,25 @@ static void exec_command(const char *cmd) {
         }
         free(argv);
         exit(EXIT_FAILURE);
+    } else { // Parent process
+        // Block until child exits
+        int status;
+        pid_t wpid = waitpid(pid, &status, 0);
+
+        if (wpid == -1) {
+            perror("waitpid");
+            exit(EXIT_FAILURE);
+        }
+
+        // Log when child process exited(normally) with an error
+        if (WIFEXITED(status) && WEXITSTATUS(status) != 0) {
+            printf("[Wolf] - Child process exited with status %d\n", WEXITSTATUS(status));
+        }
+
+        // Log when child process was terminated by a signal
+        if (WIFSIGNALED(status)) {
+            printf("[Wolf] - Child process wass terminated by signal %d\n", WTERMSIG(status));
+        }
     }
 }