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 <dpervushin@embeddedalley.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

1 files changed, 92 insertions, 16 deletions

diff --git a/drivers/mtd/ubi/kapi.c b/drivers/mtd/ubi/kapi.c
index 2675207c5fe3..88a72e9c8beb 100644
--- a/drivers/mtd/ubi/kapi.c
+++ b/drivers/mtd/ubi/kapi.c
@@ -26,6 +26,24 @@
 #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
@@ -39,33 +57,24 @@ int ubi_get_device_info(int ubi_num, struct ubi_device_info *di)
 
 	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;
@@ -79,6 +88,17 @@ void ubi_get_volume_info(struct ubi_volume_desc *desc,
 	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);
 
 /**
@@ -561,7 +581,7 @@ int ubi_leb_unmap(struct ubi_volume_desc *desc, int lnum)
 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
@@ -659,3 +679,59 @@ int ubi_sync(int ubi_num)
 	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);