RFC: libusual piggybacks the class mechanism

[Pete Zaitcev]

Hi, Greg:

I would like you to opine about a fix which I wrote for libusual.
First, the patch:

diff -urp -X dontdiff linux-2.6.18/drivers/usb/storage/libusual.c linux-2.6.18-ub/drivers/usb/storage/libusual.c
--- linux-2.6.18/drivers/usb/storage/libusual.c	2006-04-10 23:26:03.000000000 -0700
+++ linux-2.6.18-ub/drivers/usb/storage/libusual.c	2006-10-15 23:46:52.000000000 -0700
@@ -5,6 +5,7 @@
  */
 #include <linux/kernel.h>
 #include <linux/module.h>
+#include <linux/device.h>
 #include <linux/usb.h>
 #include <linux/usb_usual.h>
 #include <linux/vmalloc.h>
@@ -13,6 +14,7 @@
  */
 #define USU_MOD_FL_THREAD   1	/* Thread is running */
 #define USU_MOD_FL_PRESENT  2	/* The module is loaded */
+#define USU_MOD_FL_FAILED   3	/* The module failed to load */
 
 struct mod_status {
 	unsigned long fls;
@@ -33,8 +35,12 @@ static DECLARE_MUTEX_LOCKED(usu_init_not
 static DECLARE_COMPLETION(usu_end_notify);
 static atomic_t total_threads = ATOMIC_INIT(0);
 
+static int usu_kick(unsigned long type);
 static int usu_probe_thread(void *arg);
 
+static struct class *usu_class;
+static struct class_device *usu_class_device;
+
 /*
  * The table.
  */
@@ -113,16 +119,44 @@ EXPORT_SYMBOL_GPL(usb_usual_check_type);
 
 /*
  */
+static int usu_uevent(struct class_device *class_dev,
+    char **envp, int num_envp, char *buffer, int buffer_size)
+{
+	unsigned long flags;
+	int i;
+
+ /* P3 */ printk("libusual: uevent\n");
+	for (i = 1; i < 3; i++) {
+		spin_lock_irqsave(&usu_lock, flags);
+		if (stat[i].fls & USU_MOD_FL_FAILED) {
+ /* P3 */ printk("libusual: kicking %s\n", bias_names[i]);
+			stat[i].fls &= ~USU_MOD_FL_FAILED;
+			spin_unlock_irqrestore(&usu_lock, flags);
+			usu_kick(i);
+		} else {
+			spin_unlock_irqrestore(&usu_lock, flags);
+		}
+	}
+	return 0;
+}
+
+/*
+ */
 static int usu_probe(struct usb_interface *intf,
 			 const struct usb_device_id *id)
 {
 	unsigned long type;
-	int rc;
-	unsigned long flags;
 
 	type = USB_US_TYPE(id->driver_info);
 	if (type == 0)
 		type = atomic_read(&usu_bias);
+	return usu_kick(type);
+}
+
+static int usu_kick(unsigned long type)
+{
+	int rc;
+	unsigned long flags;
 
 	spin_lock_irqsave(&usu_lock, flags);
 	if ((stat[type].fls & (USU_MOD_FL_THREAD|USU_MOD_FL_PRESENT)) != 0) {
@@ -186,10 +220,14 @@ static int usu_probe_thread(void *arg)
 	if (rc == 0 && (st->fls & USU_MOD_FL_PRESENT) == 0) {
 		/*
 		 * This should not happen, but let us keep tabs on it.
+		 * One common source of this a user who builds USB statically,
+		 * then uses initrd, and has a USB device. When static devices
+		 * are probed, request_module() calls a fake modprobe and fails.
 		 */
 		printk(KERN_NOTICE "libusual: "
-		    "modprobe for %s succeeded, but module is not present\n",
+		    "request for %s succeeded, but module is not present\n",
 		    bias_names[type]);
+		st->fls |= USU_MOD_FL_FAILED;
 	}
 	st->fls &= ~USU_MOD_FL_THREAD;
 	spin_unlock_irqrestore(&usu_lock, flags);
@@ -203,9 +241,27 @@ static int __init usb_usual_init(void)
 {
 	int rc;
 
+	usu_class = class_create(THIS_MODULE, "libusual");
+	if (IS_ERR(usu_class)) {
+		rc = PTR_ERR(usu_class_device);
+		goto err_class;
+	}
+	usu_class_device = class_device_create(usu_class, NULL, 0, NULL, "0");
+	if (IS_ERR(usu_class_device)) {
+		rc = PTR_ERR(usu_class_device);
+		goto err_classdev;
+	}
+	usu_class_device->uevent = usu_uevent;
+
 	rc = usb_register(&usu_driver);
 	up(&usu_init_notify);
 	return rc;
+
+	// class_device_destroy(usu_class, 0);
+err_classdev:
+	class_destroy(usu_class);
+err_class:
+	return rc;
 }
 
 static void __exit usb_usual_exit(void)
@@ -221,6 +277,9 @@ static void __exit usb_usual_exit(void)
 		wait_for_completion(&usu_end_notify);
 		atomic_dec(&total_threads);
 	}
+
+	class_device_destroy(usu_class, 0);
+	class_destroy(usu_class);
 }
 
 /*

This is a patch for our bug 204396:
 https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=204396
The summary is: a USB storage device is not recognized if plugged in
before a reboot on a Fedora Core 6 Test 3.

As usual, several circumstances have to occur for this to happen.
What makes Fedora differend is how its USB core is built in statically.
This makes libusual to be static (it's an artefact of my ineptness with
Kconfig language, and also nash's modprobe not loading dependencies),
and this splits it off storage (sub)modules.

The patch abuses the class mechanism to receive a signal from udev
when it's ready and thus request_module can be retried.

How acceptable is this?

-- Pete

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