UBI: add notification API

UBI volume notifications are intended to create the API to get clients
notified about volume creation/deletion, renaming and re-sizing. A
client can subscribe to these notifications using 'ubi_volume_register()'
and cancel the subscription using 'ubi_volume_unregister()'. When UBI
volumes change, a blocking notifier is called. Clients also can request
"added" events on all volumes that existed before client subscribed
to the notifications.

If we use notifications instead of calling functions like 'ubi_gluebi_xxx()',
we can make the MTD emulation layer to be more flexible: build it as a
separate module and load/unload it on demand.

[Artem: many cleanups, rework locking, add "updated" event, provide
device/volume info in notifiers]

Signed-off-by: Dmitry Pervushin <[e-mail]>
Signed-off-by: Artem Bityutskiy <[e-mail]>

drivers/mtd/ubi/build.c

···
 	__ATTR(mtd_num, S_IRUGO, dev_attribute_show, NULL);
 
 /**
+ * ubi_volume_notify - send a volume change notification.
+ * @ubi: UBI device description object
+ * @vol: volume description object of the changed volume
+ * @ntype: notification type to send (%UBI_VOLUME_ADDED, etc)
+ *
+ * This is a helper function which notifies all subscribers about a volume
+ * change event (creation, removal, re-sizing, re-naming, updating). Returns
+ * zero in case of success and a negative error code in case of failure.
+ */
+int ubi_volume_notify(struct ubi_device *ubi, struct ubi_volume *vol, int ntype)
+{
+	struct ubi_notification nt;
+
+	ubi_do_get_device_info(ubi, &nt.di);
+	ubi_do_get_volume_info(ubi, vol, &nt.vi);
+	return blocking_notifier_call_chain(&ubi_notifiers, ntype, &nt);
+}
+
+/**
+ * ubi_notify_all - send a notification to all volumes.
+ * @ubi: UBI device description object
+ * @ntype: notification type to send (%UBI_VOLUME_ADDED, etc)
+ * @nb: the notifier to call
+ *
+ * This function walks all volumes of UBI device @ubi and sends the @ntype
+ * notification for each volume. If @nb is %NULL, then all registered notifiers
+ * are called, otherwise only the @nb notifier is called. Returns the number of
+ * sent notifications.
+ */
+int ubi_notify_all(struct ubi_device *ubi, int ntype, struct notifier_block *nb)
+{
+	struct ubi_notification nt;
+	int i, count = 0;
+
+	ubi_do_get_device_info(ubi, &nt.di);
+
+	mutex_lock(&ubi->device_mutex);
+	for (i = 0; i < ubi->vtbl_slots; i++) {
+		/*
+		 * Since the @ubi->device is locked, and we are not going to
+		 * change @ubi->volumes, we do not have to lock
+		 * @ubi->volumes_lock.
+		 */
+		if (!ubi->volumes[i])
+			continue;
+
+		ubi_do_get_volume_info(ubi, ubi->volumes[i], &nt.vi);
+		if (nb)
+			nb->notifier_call(nb, ntype, &nt);
+		else
+			blocking_notifier_call_chain(&ubi_notifiers, ntype,
+						     &nt);
+		count += 1;
+	}
+	mutex_unlock(&ubi->device_mutex);
+
+	return count;
+}
+
+/**
+ * ubi_enumerate_volumes - send "add" notification for all existing volumes.
+ * @nb: the notifier to call
+ *
+ * This function walks all UBI devices and volumes and sends the
+ * %UBI_VOLUME_ADDED notification for each volume. If @nb is %NULL, then all
+ * registered notifiers are called, otherwise only the @nb notifier is called.
+ * Returns the number of sent notifications.
+ */
+int ubi_enumerate_volumes(struct notifier_block *nb)
+{
+	int i, count = 0;
+
+	/*
+	 * Since the @ubi_devices_mutex is locked, and we are not going to
+	 * change @ubi_devices, we do not have to lock @ubi_devices_lock.
+	 */
+	for (i = 0; i < UBI_MAX_DEVICES; i++) {
+		struct ubi_device *ubi = ubi_devices[i];
+
+		if (!ubi)
+			continue;
+		count += ubi_notify_all(ubi, UBI_VOLUME_ADDED, nb);
+	}
+
+	return count;
+}
+
+/**
  * ubi_get_device - get UBI device.
  * @ubi_num: UBI device number
  *
···
 	spin_unlock(&ubi->wl_lock);
 
 	ubi_devices[ubi_num] = ubi;
+	ubi_notify_all(ubi, UBI_VOLUME_ADDED, NULL);
 	return ubi_num;
 
 out_uif:
···
 	if (ubi_num < 0 || ubi_num >= UBI_MAX_DEVICES)
 		return -EINVAL;
 
-	spin_lock(&ubi_devices_lock);
-	ubi = ubi_devices[ubi_num];
-	if (!ubi) {
-		spin_unlock(&ubi_devices_lock);
+	ubi = ubi_get_device(ubi_num);
+	if (!ubi)
 		return -EINVAL;
-	}
 
+	spin_lock(&ubi_devices_lock);
+	put_device(&ubi->dev);
+	ubi->ref_count -= 1;
 	if (ubi->ref_count) {
 		if (!anyway) {
 			spin_unlock(&ubi_devices_lock);
···
 	spin_unlock(&ubi_devices_lock);
 
 	ubi_assert(ubi_num == ubi->ubi_num);
+	ubi_notify_all(ubi, UBI_VOLUME_REMOVED, NULL);
 	dbg_msg("detaching mtd%d from ubi%d", ubi->mtd->index, ubi_num);
 
 	/*

drivers/mtd/ubi/cdev.c

···
 		}
 		vol->checked = 1;
 		ubi_gluebi_updated(vol);
+		ubi_volume_notify(ubi, vol, UBI_VOLUME_UPDATED);
 		revoke_exclusive(desc, UBI_READWRITE);
 	}
 

drivers/mtd/ubi/kapi.c

···
 #include "ubi.h"
 
 /**
+ * ubi_do_get_device_info - get information about UBI device.
+ * @ubi: UBI device description object
+ * @di: the information is stored here
+ *
+ * This function is the same as 'ubi_get_device_info()', but it assumes the UBI
+ * device is locked and cannot disappear.
+ */
+void ubi_do_get_device_info(struct ubi_device *ubi, struct ubi_device_info *di)
+{
+	di->ubi_num = ubi->ubi_num;
+	di->leb_size = ubi->leb_size;
+	di->min_io_size = ubi->min_io_size;
+	di->ro_mode = ubi->ro_mode;
+	di->cdev = ubi->cdev.dev;
+}
+EXPORT_SYMBOL_GPL(ubi_do_get_device_info);
+
+/**
  * ubi_get_device_info - get information about UBI device.
  * @ubi_num: UBI device number
  * @di: the information is stored here
···
 
 	if (ubi_num < 0 || ubi_num >= UBI_MAX_DEVICES)
 		return -EINVAL;
-
 	ubi = ubi_get_device(ubi_num);
 	if (!ubi)
 		return -ENODEV;
-
-	di->ubi_num = ubi->ubi_num;
-	di->leb_size = ubi->leb_size;
-	di->min_io_size = ubi->min_io_size;
-	di->ro_mode = ubi->ro_mode;
-	di->cdev = ubi->cdev.dev;
-
+	ubi_do_get_device_info(ubi, di);
 	ubi_put_device(ubi);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(ubi_get_device_info);
 
 /**
- * ubi_get_volume_info - get information about UBI volume.
- * @desc: volume descriptor
+ * ubi_do_get_volume_info - get information about UBI volume.
+ * @ubi: UBI device description object
+ * @vol: volume description object
  * @vi: the information is stored here
  */
-void ubi_get_volume_info(struct ubi_volume_desc *desc,
-			 struct ubi_volume_info *vi)
+void ubi_do_get_volume_info(struct ubi_device *ubi, struct ubi_volume *vol,
+			    struct ubi_volume_info *vi)
 {
-	const struct ubi_volume *vol = desc->vol;
-	const struct ubi_device *ubi = vol->ubi;
-
 	vi->vol_id = vol->vol_id;
 	vi->ubi_num = ubi->ubi_num;
 	vi->size = vol->reserved_pebs;
···
 	vi->name_len = vol->name_len;
 	vi->name = vol->name;
 	vi->cdev = vol->cdev.dev;
+}
+
+/**
+ * ubi_get_volume_info - get information about UBI volume.
+ * @desc: volume descriptor
+ * @vi: the information is stored here
+ */
+void ubi_get_volume_info(struct ubi_volume_desc *desc,
+			 struct ubi_volume_info *vi)
+{
+	ubi_do_get_volume_info(desc->vol->ubi, desc->vol, vi);
 }
 EXPORT_SYMBOL_GPL(ubi_get_volume_info);
 
···
 EXPORT_SYMBOL_GPL(ubi_leb_unmap);
 
 /**
- * ubi_leb_map - map logical erasblock to a physical eraseblock.
+ * ubi_leb_map - map logical eraseblock to a physical eraseblock.
  * @desc: volume descriptor
  * @lnum: logical eraseblock number
  * @dtype: expected data type
···
 	return 0;
 }
 EXPORT_SYMBOL_GPL(ubi_sync);
+
+BLOCKING_NOTIFIER_HEAD(ubi_notifiers);
+
+/**
+ * ubi_register_volume_notifier - register a volume notifier.
+ * @nb: the notifier description object
+ * @ignore_existing: if non-zero, do not send "added" notification for all
+ *                   already existing volumes
+ *
+ * This function registers a volume notifier, which means that
+ * 'nb->notifier_call()' will be invoked when an UBI  volume is created,
+ * removed, re-sized, re-named, or updated. The first argument of the function
+ * is the notification type. The second argument is pointer to a
+ * &struct ubi_notification object which describes the notification event.
+ * Using UBI API from the volume notifier is prohibited.
+ *
+ * This function returns zero in case of success and a negative error code
+ * in case of failure.
+ */
+int ubi_register_volume_notifier(struct notifier_block *nb,
+				 int ignore_existing)
+{
+	int err;
+
+	err = blocking_notifier_chain_register(&ubi_notifiers, nb);
+	if (err != 0)
+		return err;
+	if (ignore_existing)
+		return 0;
+
+	/*
+	 * We are going to walk all UBI devices and all volumes, and
+	 * notify the user about existing volumes by the %UBI_VOLUME_ADDED
+	 * event. We have to lock the @ubi_devices_mutex to make sure UBI
+	 * devices do not disappear.
+	 */
+	mutex_lock(&ubi_devices_mutex);
+	ubi_enumerate_volumes(nb);
+	mutex_unlock(&ubi_devices_mutex);
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(ubi_register_volume_notifier);
+
+/**
+ * ubi_unregister_volume_notifier - unregister the volume notifier.
+ * @nb: the notifier description object
+ *
+ * This function unregisters volume notifier @nm and returns zero in case of
+ * success and a negative error code in case of failure.
+ */
+int ubi_unregister_volume_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_unregister(&ubi_notifiers, nb);
+}
+EXPORT_SYMBOL_GPL(ubi_unregister_volume_notifier);

drivers/mtd/ubi/ubi.h

···
 #include <linux/vmalloc.h>
 #include <linux/mtd/mtd.h>
 #include <linux/mtd/ubi.h>
+#include <linux/notifier.h>
 
 #include "ubi-media.h"
 #include "scan.h"
···
 extern const struct file_operations ubi_vol_cdev_operations;
 extern struct class *ubi_class;
 extern struct mutex ubi_devices_mutex;
+extern struct blocking_notifier_head ubi_notifiers;
 
 /* vtbl.c */
 int ubi_change_vtbl_record(struct ubi_device *ubi, int idx,
···
 void ubi_put_device(struct ubi_device *ubi);
 struct ubi_device *ubi_get_by_major(int major);
 int ubi_major2num(int major);
+int ubi_volume_notify(struct ubi_device *ubi, struct ubi_volume *vol,
+		      int ntype);
+int ubi_notify_all(struct ubi_device *ubi, int ntype,
+		   struct notifier_block *nb);
+int ubi_enumerate_volumes(struct notifier_block *nb);
+
+/* kapi.c */
+void ubi_do_get_device_info(struct ubi_device *ubi, struct ubi_device_info *di);
+void ubi_do_get_volume_info(struct ubi_device *ubi, struct ubi_volume *vol,
+			    struct ubi_volume_info *vi);
 
 /*
  * ubi_rb_for_each_entry - walk an RB-tree.

drivers/mtd/ubi/vmt.c

···
 	ubi->vol_count += 1;
 	spin_unlock(&ubi->volumes_lock);
 
+	ubi_volume_notify(ubi, vol, UBI_VOLUME_ADDED);
 	if (paranoid_check_volumes(ubi))
 		dbg_err("check failed while creating volume %d", vol_id);
 	return err;
···
 	ubi->vol_count -= 1;
 	spin_unlock(&ubi->volumes_lock);
 
+	ubi_volume_notify(ubi, vol, UBI_VOLUME_REMOVED);
 	if (!no_vtbl && paranoid_check_volumes(ubi))
 		dbg_err("check failed while removing volume %d", vol_id);
 
···
 			(long long)vol->used_ebs * vol->usable_leb_size;
 	}
 
+	ubi_volume_notify(ubi, vol, UBI_VOLUME_RESIZED);
 	if (paranoid_check_volumes(ubi))
 		dbg_err("check failed while re-sizing volume %d", vol_id);
 	return err;
···
 			vol->name_len = re->new_name_len;
 			memcpy(vol->name, re->new_name, re->new_name_len + 1);
 			spin_unlock(&ubi->volumes_lock);
+			ubi_volume_notify(ubi, vol, UBI_VOLUME_RENAMED);
 		}
 	}
 

include/linux/mtd/ubi.h

···
 	dev_t cdev;
 };
 
+/*
+ * enum - volume notification types.
+ * @UBI_VOLUME_ADDED: volume has been added
+ * @UBI_VOLUME_REMOVED: start volume volume
+ * @UBI_VOLUME_RESIZED: volume size has been re-sized
+ * @UBI_VOLUME_RENAMED: volume name has been re-named
+ * @UBI_VOLUME_UPDATED: volume name has been updated
+ *
+ * These constants define which type of event has happened when a volume
+ * notification function is invoked.
+ */
+enum {
+	UBI_VOLUME_ADDED,
+	UBI_VOLUME_REMOVED,
+	UBI_VOLUME_RESIZED,
+	UBI_VOLUME_RENAMED,
+	UBI_VOLUME_UPDATED,
+};
+
+/*
+ * struct ubi_notification - UBI notification description structure.
+ * @di: UBI device description object
+ * @vi: UBI volume description object
+ *
+ * UBI notifiers are called with a pointer to an object of this type. The
+ * object describes the notification. Namely, it provides a description of the
+ * UBI device and UBI volume the notification informs about.
+ */
+struct ubi_notification {
+	struct ubi_device_info di;
+	struct ubi_volume_info vi;
+};
+
 /* UBI descriptor given to users when they open UBI volumes */
 struct ubi_volume_desc;
 
···
 struct ubi_volume_desc *ubi_open_volume(int ubi_num, int vol_id, int mode);
 struct ubi_volume_desc *ubi_open_volume_nm(int ubi_num, const char *name,
 					   int mode);
+int ubi_register_volume_notifier(struct notifier_block *nb,
+				 int ignore_existing);
+int ubi_unregister_volume_notifier(struct notifier_block *nb);
+
 void ubi_close_volume(struct ubi_volume_desc *desc);
 int ubi_leb_read(struct ubi_volume_desc *desc, int lnum, char *buf, int offset,
 		 int len, int check);