wwan_hwsim: add debugfs management interface

wwan_hwsim creates and removes simulated control ports on module loading
and unloading. It would be helpful to be able to create/remove devices
and ports at run-time to trigger wwan port (un-)register actions without
module reloading.

Some simulator objects (e.g. ports) do not have the underling device and
it is not possible to fully manage the simulator via sysfs. wwan_hsim
intend for developers, so implement it as a self-contained debugfs based
management interface.

Signed-off-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/wwan/wwan_hwsim.c

@@ -15,6 +15,8 @@
 #include <linux/list.h>
 #include <linux/skbuff.h>
 #include <linux/wwan.h>
+#include <linux/debugfs.h>
+#include <linux/workqueue.h>
 
 static int wwan_hwsim_devsnum = 2;
 module_param_named(devices, wwan_hwsim_devsnum, int, 0444);
@@ -22,6 +24,9 @@ MODULE_PARM_DESC(devices, "Number of simulated devices");
 
 static struct class *wwan_hwsim_class;
 
+static struct dentry *wwan_hwsim_debugfs_topdir;
+static struct dentry *wwan_hwsim_debugfs_devcreate;
+
 static DEFINE_SPINLOCK(wwan_hwsim_devs_lock);
 static LIST_HEAD(wwan_hwsim_devs);
 static unsigned int wwan_hwsim_dev_idx;
@@ -30,6 +35,9 @@ struct wwan_hwsim_dev {
 	struct list_head list;
 	unsigned int id;
 	struct device dev;
+	struct work_struct del_work;
+	struct dentry *debugfs_topdir;
+	struct dentry *debugfs_portcreate;
 	spinlock_t ports_lock;	/* Serialize ports creation/deletion */
 	unsigned int port_idx;
 	struct list_head ports;
@@ -40,6 +48,8 @@ struct wwan_hwsim_port {
 	unsigned int id;
 	struct wwan_hwsim_dev *dev;
 	struct wwan_port *wwan;
+	struct work_struct del_work;
+	struct dentry *debugfs_topdir;
 	enum {			/* AT command parser state */
 		AT_PARSER_WAIT_A,
 		AT_PARSER_WAIT_T,
@@ -48,6 +58,12 @@ struct wwan_hwsim_port {
 	} pstate;
 };
 
+static const struct file_operations wwan_hwsim_debugfs_portdestroy_fops;
+static const struct file_operations wwan_hwsim_debugfs_portcreate_fops;
+static const struct file_operations wwan_hwsim_debugfs_devdestroy_fops;
+static void wwan_hwsim_port_del_work(struct work_struct *work);
+static void wwan_hwsim_dev_del_work(struct work_struct *work);
+
 static int wwan_hwsim_port_start(struct wwan_port *wport)
 {
 	struct wwan_hwsim_port *port = wwan_port_get_drvdata(wport);
@@ -139,6 +155,7 @@ static const struct wwan_port_ops wwan_hwsim_port_ops = {
 static struct wwan_hwsim_port *wwan_hwsim_port_new(struct wwan_hwsim_dev *dev)
 {
 	struct wwan_hwsim_port *port;
+	char name[0x10];
 	int err;
 
 	port = kzalloc(sizeof(*port), GFP_KERNEL);
@@ -159,6 +176,13 @@ static struct wwan_hwsim_port *wwan_hwsim_port_new(struct wwan_hwsim_dev *dev)
 		goto err_free_port;
 	}
 
+	INIT_WORK(&port->del_work, wwan_hwsim_port_del_work);
+
+	snprintf(name, sizeof(name), "port%u", port->id);
+	port->debugfs_topdir = debugfs_create_dir(name, dev->debugfs_topdir);
+	debugfs_create_file("destroy", 0200, port->debugfs_topdir, port,
+			    &wwan_hwsim_debugfs_portdestroy_fops);
+
 	return port;
 
 err_free_port:
@@ -169,10 +193,34 @@ err_free_port:
 
 static void wwan_hwsim_port_del(struct wwan_hwsim_port *port)
 {
+	debugfs_remove(port->debugfs_topdir);
+
+	/* Make sure that there is no pending deletion work */
+	if (current_work() != &port->del_work)
+		cancel_work_sync(&port->del_work);
+
 	wwan_remove_port(port->wwan);
 	kfree(port);
 }
 
+static void wwan_hwsim_port_del_work(struct work_struct *work)
+{
+	struct wwan_hwsim_port *port =
+				container_of(work, typeof(*port), del_work);
+	struct wwan_hwsim_dev *dev = port->dev;
+
+	spin_lock(&dev->ports_lock);
+	if (list_empty(&port->list)) {
+		/* Someone else deleting port at the moment */
+		spin_unlock(&dev->ports_lock);
+		return;
+	}
+	list_del_init(&port->list);
+	spin_unlock(&dev->ports_lock);
+
+	wwan_hwsim_port_del(port);
+}
+
 static void wwan_hwsim_dev_release(struct device *sysdev)
 {
 	struct wwan_hwsim_dev *dev = container_of(sysdev, typeof(*dev), dev);
@@ -204,6 +252,17 @@ static struct wwan_hwsim_dev *wwan_hwsim_dev_new(void)
 	if (err)
 		goto err_free_dev;
 
+	INIT_WORK(&dev->del_work, wwan_hwsim_dev_del_work);
+
+	dev->debugfs_topdir = debugfs_create_dir(dev_name(&dev->dev),
+						 wwan_hwsim_debugfs_topdir);
+	debugfs_create_file("destroy", 0200, dev->debugfs_topdir, dev,
+			    &wwan_hwsim_debugfs_devdestroy_fops);
+	dev->debugfs_portcreate =
+		debugfs_create_file("portcreate", 0200,
+				    dev->debugfs_topdir, dev,
+				    &wwan_hwsim_debugfs_portcreate_fops);
+
 	return dev;
 
 err_free_dev:
@@ -214,23 +273,136 @@ err_free_dev:
 
 static void wwan_hwsim_dev_del(struct wwan_hwsim_dev *dev)
 {
+	debugfs_remove(dev->debugfs_portcreate);	/* Avoid new ports */
+
 	spin_lock(&dev->ports_lock);
 	while (!list_empty(&dev->ports)) {
 		struct wwan_hwsim_port *port;
 
 		port = list_first_entry(&dev->ports, struct wwan_hwsim_port,
 					list);
-		list_del(&port->list);
+		list_del_init(&port->list);
 		spin_unlock(&dev->ports_lock);
 		wwan_hwsim_port_del(port);
 		spin_lock(&dev->ports_lock);
 	}
 	spin_unlock(&dev->ports_lock);
 
+	debugfs_remove(dev->debugfs_topdir);
+
+	/* Make sure that there is no pending deletion work */
+	if (current_work() != &dev->del_work)
+		cancel_work_sync(&dev->del_work);
+
 	device_unregister(&dev->dev);
 	/* Memory will be freed in the device release callback */
 }
 
+static void wwan_hwsim_dev_del_work(struct work_struct *work)
+{
+	struct wwan_hwsim_dev *dev = container_of(work, typeof(*dev), del_work);
+
+	spin_lock(&wwan_hwsim_devs_lock);
+	if (list_empty(&dev->list)) {
+		/* Someone else deleting device at the moment */
+		spin_unlock(&wwan_hwsim_devs_lock);
+		return;
+	}
+	list_del_init(&dev->list);
+	spin_unlock(&wwan_hwsim_devs_lock);
+
+	wwan_hwsim_dev_del(dev);
+}
+
+static ssize_t wwan_hwsim_debugfs_portdestroy_write(struct file *file,
+						    const char __user *usrbuf,
+						    size_t count, loff_t *ppos)
+{
+	struct wwan_hwsim_port *port = file->private_data;
+
+	/* We can not delete port here since it will cause a deadlock due to
+	 * waiting this callback to finish in the debugfs_remove() call. So,
+	 * use workqueue.
+	 */
+	schedule_work(&port->del_work);
+
+	return count;
+}
+
+static const struct file_operations wwan_hwsim_debugfs_portdestroy_fops = {
+	.write = wwan_hwsim_debugfs_portdestroy_write,
+	.open = simple_open,
+	.llseek = noop_llseek,
+};
+
+static ssize_t wwan_hwsim_debugfs_portcreate_write(struct file *file,
+						   const char __user *usrbuf,
+						   size_t count, loff_t *ppos)
+{
+	struct wwan_hwsim_dev *dev = file->private_data;
+	struct wwan_hwsim_port *port;
+
+	port = wwan_hwsim_port_new(dev);
+	if (IS_ERR(port))
+		return PTR_ERR(port);
+
+	spin_lock(&dev->ports_lock);
+	list_add_tail(&port->list, &dev->ports);
+	spin_unlock(&dev->ports_lock);
+
+	return count;
+}
+
+static const struct file_operations wwan_hwsim_debugfs_portcreate_fops = {
+	.write = wwan_hwsim_debugfs_portcreate_write,
+	.open = simple_open,
+	.llseek = noop_llseek,
+};
+
+static ssize_t wwan_hwsim_debugfs_devdestroy_write(struct file *file,
+						   const char __user *usrbuf,
+						   size_t count, loff_t *ppos)
+{
+	struct wwan_hwsim_dev *dev = file->private_data;
+
+	/* We can not delete device here since it will cause a deadlock due to
+	 * waiting this callback to finish in the debugfs_remove() call. So,
+	 * use workqueue.
+	 */
+	schedule_work(&dev->del_work);
+
+	return count;
+}
+
+static const struct file_operations wwan_hwsim_debugfs_devdestroy_fops = {
+	.write = wwan_hwsim_debugfs_devdestroy_write,
+	.open = simple_open,
+	.llseek = noop_llseek,
+};
+
+static ssize_t wwan_hwsim_debugfs_devcreate_write(struct file *file,
+						  const char __user *usrbuf,
+						  size_t count, loff_t *ppos)
+{
+	struct wwan_hwsim_dev *dev;
+
+	dev = wwan_hwsim_dev_new();
+	if (IS_ERR(dev))
+		return PTR_ERR(dev);
+
+	spin_lock(&wwan_hwsim_devs_lock);
+	list_add_tail(&dev->list, &wwan_hwsim_devs);
+	spin_unlock(&wwan_hwsim_devs_lock);
+
+	return count;
+}
+
+static const struct file_operations wwan_hwsim_debugfs_devcreate_fops = {
+	.write = wwan_hwsim_debugfs_devcreate_write,
+	.open = simple_open,
+	.llseek = noop_llseek,
+};
+
 static int __init wwan_hwsim_init_devs(void)
 {
 	struct wwan_hwsim_dev *dev;
@@ -272,7 +444,7 @@ static void wwan_hwsim_free_devs(void)
 	while (!list_empty(&wwan_hwsim_devs)) {
 		dev = list_first_entry(&wwan_hwsim_devs, struct wwan_hwsim_dev,
 				       list);
-		list_del(&dev->list);
+		list_del_init(&dev->list);
 		spin_unlock(&wwan_hwsim_devs_lock);
 		wwan_hwsim_dev_del(dev);
 		spin_lock(&wwan_hwsim_devs_lock);
@@ -291,6 +463,12 @@ static int __init wwan_hwsim_init(void)
 	if (IS_ERR(wwan_hwsim_class))
 		return PTR_ERR(wwan_hwsim_class);
 
+	wwan_hwsim_debugfs_topdir = debugfs_create_dir("wwan_hwsim", NULL);
+	wwan_hwsim_debugfs_devcreate =
+			debugfs_create_file("devcreate", 0200,
+					    wwan_hwsim_debugfs_topdir, NULL,
+					    &wwan_hwsim_debugfs_devcreate_fops);
+
 	err = wwan_hwsim_init_devs();
 	if (err)
 		goto err_clean_devs;
@@ -299,6 +477,7 @@ static int __init wwan_hwsim_init(void)
 
 err_clean_devs:
 	wwan_hwsim_free_devs();
+	debugfs_remove(wwan_hwsim_debugfs_topdir);
 	class_destroy(wwan_hwsim_class);
 
 	return err;
@@ -306,7 +485,10 @@ err_clean_devs:
 
 static void __exit wwan_hwsim_exit(void)
 {
+	debugfs_remove(wwan_hwsim_debugfs_devcreate);	/* Avoid new devs */
 	wwan_hwsim_free_devs();
+	flush_scheduled_work();		/* Wait deletion works completion */
+	debugfs_remove(wwan_hwsim_debugfs_topdir);
 	class_destroy(wwan_hwsim_class);
 }