only allow one writer

lab6/.vscode/settings.json

@@ -1,9 +1,5 @@
 {
     "files.associations": {
-        "cdev.h": "c",
-        "module.h": "c",
-        "types.h": "c",
-        "init.h": "c",
         "any": "cpp",
         "array": "cpp",
         "atomic": "cpp",
@@ -72,13 +68,11 @@
         "stdfloat": "cpp",
         "stop_token": "cpp",
         "streambuf": "cpp",
+        "syncstream": "cpp",
         "text_encoding": "cpp",
         "thread": "cpp",
         "cinttypes": "cpp",
         "typeinfo": "cpp",
-        "variant": "cpp",
+        "variant": "cpp"
-        "csignal": "cpp",
+    }
-        "syncstream": "cpp"
-    },
-    "C_Cpp.default.compilerPath": "/usr/bin/clang++"
 }

lab6/Makefile

@@ -1,18 +1,18 @@
 obj-m += wendy.o
 OUT_DIR := build
 
-.PHONY: all kern_mod install uninstall clean reader writer tester dirprepare
+.PHONY: all kern_mod install rm clean reader writer tester dirprepare
 
 all: kern_mod reader writer tester
 
-kern_mod: wendy.c
+kern_mod:
-	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) MO=$(PWD)/build/kern
+	make -C wendy_mod
 
-install:
+install: kern_mod
-	sudo insmod ./build/kern/wendy.ko
+	make -C wendy_mod install
 
-uninstall:
+rm:
-	sudo rmmod wendy
+	make -C wendy_mod uninstall
 
 reader: dirprepare
 	gcc pipe_read.c -o $(OUT_DIR)/pread
@@ -27,6 +27,6 @@ dirprepare:
 	mkdir -p $(OUT_DIR)
 
 clean:
-	$(MAKE) -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
+	make -C wendy_mod clean
 	rm -rf $(OUT_DIR)
 

lab6/pipe_tester.cpp

@@ -7,60 +7,22 @@
 void writer() {
     std::osyncstream(std::cout) << "Writer started" << std::endl;
     
-    char *buffer = new char[8192];
+    std::ofstream pipe_write("/dev/wendy_in");
-    
+    pipe_write << "Hello from the other side\n";
-    for (int i = 0; i < 8192; ++i) {
+    std::osyncstream(std::cout) << "Writer ended" << std::endl;
-        buffer[i] = static_cast<char>((i % 95) + 32); // Printable range
-    }
-
-    FILE *fl = fopen("/dev/wendy_in", "w");
-    if (!fl) {
-        std::osyncstream(std::cerr) << "Cannot open wendy_in" << std::endl;
-    }
-
-    int wrote = 0;
-    wrote = fwrite(buffer, sizeof(char), 8192, fl);
-    if (wrote < 0) {
-        std::osyncstream(std::cerr) << "Write error: " << wrote << std::endl;
-    }
-    std::osyncstream(std::cout) << "Wrote " << wrote << std::endl;
-
-    std::this_thread::sleep_for(std::chrono::milliseconds(500));
-    wrote = fwrite(buffer, sizeof(char), 8192, fl);
-    if (wrote < 0) {
-        std::osyncstream(std::cerr) << "2nd write error: " << wrote << std::endl;
-    }
-    std::osyncstream(std::cout) << "2nd wrote " << wrote << std::endl;
 }
 
 void reader() {
     std::osyncstream(std::cout) << "Reader started" << std::endl;
-    FILE *fl = fopen("/dev/wendy_out", "r");
+    std::ifstream pipe_read("/dev/wendy_out");
-    if (!fl) {
+    std::osyncstream(std::cout) << "Reader read content: " << pipe_read.rdbuf();
-        std::osyncstream(std::cerr) << "Cannot open wendy_out" << std::endl;
+    std::osyncstream(std::cout) << "Reader ended" << std::endl;
-        return;
-    }
-    
-    char *buffer = new char[257];
-
-    int read = 0;
-    int total_read = 0;
-    do {
-        read = fread(buffer, sizeof(char), 100, fl);
-        if (read <= 0) {
-            break;
-        }
-        total_read += read;
-        std::osyncstream(std::cout) << "Read " << read << "bytes, content: " << buffer << ", total " << total_read << std::endl;
-    } while (1);
-
-    std::osyncstream(std::cout) << "Read failed: read = " << read << std::endl;
 }
 
 int main() {
+    std::thread writer_thread(writer);
     std::thread reader_thread(reader);
     std::this_thread::sleep_for(std::chrono::milliseconds(100));
-    std::thread writer_thread(writer);
     if (reader_thread.joinable()) {
         reader_thread.join();
     }

lab6/wendy_mod/.vscode/c_cpp_properties.json

@@ -1,7 +1,7 @@
 {
     "configurations": [
       {
-        "name": "Linux Kernel Module",
+        "name": "Linux",
         "includePath": [
           "/usr/lib/modules/6.14.3-arch1-1/build/include",
           "/usr/lib/modules/6.14.3-arch1-1/build/arch/x86/include",

lab6/wendy_mod/.vscode/settings.json

@@ -0,0 +1,8 @@
+{
+    "files.associations": {
+        "cdev.h": "c",
+        "module.h": "c",
+        "types.h": "c",
+        "init.h": "c",
+    }
+}

lab6/wendy_mod/Makefile

@@ -0,0 +1,20 @@
+obj-m += wendy.o
+OUT_DIR := build
+CUR_DIR := $(shell pwd)
+
+.PHONY: kern_mod install uninstall dirprepare clean
+
+kern_mod: wendy.c dirprepare
+	make -C /lib/modules/$(shell uname -r)/build M=$(CUR_DIR) MO=$(CUR_DIR)/$(OUT_DIR)
+
+install:
+	sudo insmod build/wendy.ko
+
+uninstall:
+	sudo rmmod wendy
+
+dirprepare:
+	mkdir -p $(CUR_DIR)/$(OUT_DIR)
+
+clean:
+	make -C /lib/modules/$(shell uname -r)/build M=$(CUR_DIR) clean

lab6/wendy_mod/wendy.c

@@ -20,6 +20,8 @@ enum MyPipeMinors {
 
 struct mypipe_data {
     struct cdev cdev;
+    // Whether opened by some writer
+    bool is_active;
     u8 buffer[MYPIPE_BUFFER_SIZE];
     size_t write_pos;
     size_t read_pos;
@@ -33,18 +35,43 @@ static struct class *mypipedev_class = NULL;
 
 // Protects the buffer
 static DEFINE_MUTEX(mypipe_lock);
+// Protects the is_active value
+static DEFINE_MUTEX(isactive_lock);
 // These are two wait_queue_head_t for storing tasks that are waiting for
 // writing/ reading
 static DECLARE_WAIT_QUEUE_HEAD(read_queue);
 static DECLARE_WAIT_QUEUE_HEAD(write_queue);
 
 static int mypipe_open(struct inode *inode, struct file *file) {
-    printk(KERN_INFO "Wendy opened.");
+    int minor = iminor(inode);
+    printk(KERN_INFO "%s opened, minor = %d", MYPIPE_DEVICE_NAME, minor);
+
+    // If its opening the writing end, we limit it to only one writer
+    if (minor == MYPIPE_MINOR_IN) {
+        if (mutex_lock_interruptible(&isactive_lock)) {
+            return -ERESTARTSYS;
+        }
+
+        if (pdata.is_active) {
+            return -EBUSY;
+        }
+        pdata.is_active = true;
+        mutex_unlock(&isactive_lock);
+    }
     return 0;
 }
 
 static int mypipe_release(struct inode *inode, struct file *file) {
-    printk(KERN_INFO "Wendy released.");
+    int minor = iminor(inode);
+    printk(KERN_INFO "%s released, minor = %d", MYPIPE_DEVICE_NAME, minor);
+
+    if (minor == MYPIPE_MINOR_IN) {
+        mutex_lock(&isactive_lock);
+        pdata.is_active = false;
+        mutex_unlock(&isactive_lock);
+        wake_up_interruptible(&read_queue);
+
+    }
     return 0;
 }
 
@@ -65,7 +92,21 @@ static ssize_t mypipe_read(struct file *filep, char __user *buf, size_t size,
     // We currently have no data, but we can wait for possible new to write in
     while (pdata.data_len == 0) {
         mutex_unlock(&mypipe_lock);
+        
+        // Check if the writer is still active
+        if (mutex_lock_interruptible(&isactive_lock)) {
+            return -ERESTARTSYS;
+        }
+        bool writer_is_active = pdata.is_active;
+        mutex_unlock(&isactive_lock);
+
+        if (!writer_is_active) {
+            return 0; // No data left and the writer is gone -> EOF for reader
+        }
+
+        // There is still writer, wait for data
         if (filep->f_flags & O_NONBLOCK) {
+            // The caller says no waiting, so we don't wait
             return -EAGAIN;
         }
         if (wait_event_interruptible(read_queue, pdata.data_len > 0)) {
@@ -211,7 +252,9 @@ static int __init mypipe_init(void) {
     device_create(mypipedev_class, NULL, MKDEV(dev_major, MYPIPE_MINOR_OUT),
                   NULL, "%s_out", MYPIPE_DEVICE_NAME);
 
-    printk(KERN_INFO "Wendy: module loaded\n");
+    pdata.is_active = false;
+
+    printk(KERN_INFO "%s: module loaded\n", MYPIPE_DEVICE_NAME);
     return 0;
 
 del_cdev:
@@ -229,7 +272,7 @@ static void __exit mypipe_destroy(void) {
     class_destroy(mypipedev_class);
     cdev_del(&pdata.cdev);
     unregister_chrdev_region(MKDEV(dev_major, 0), MYPIPE_MINOR_COUNT);
-    printk(KERN_INFO "Wendy: module unloaded");
+    printk(KERN_INFO "%s: module unloaded", MYPIPE_DEVICE_NAME);
 }
 
 module_init(mypipe_init);