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Subject[PATCH 4/9] dm: Update dm-uevent.txt
Document the current dm uevent API, as modified by this patchset.

Signed-off-by: Andy Grover <>
Documentation/device-mapper/dm-uevent.txt | 49 ++++++++++++++++++++++++++-----
1 file changed, 42 insertions(+), 7 deletions(-)

diff --git a/Documentation/device-mapper/dm-uevent.txt b/Documentation/device-mapper/dm-uevent.txt
index 07edbd85..0a5d909 100644
--- a/Documentation/device-mapper/dm-uevent.txt
+++ b/Documentation/device-mapper/dm-uevent.txt
@@ -1,18 +1,53 @@
The device-mapper uevent code adds the capability to device-mapper to create
and send kobject uevents (uevents). Previously device-mapper events were only
-available through the ioctl interface. The advantage of the uevents interface
-is the event contains environment attributes providing increased context for
+available through the ioctl interface. The advantages of the uevents interface
+are the event contains environment attributes providing increased context for
the event avoiding the need to query the state of the device-mapper device after
-the event is received.
+the event is received, and uevents are poll()-able in userspace, whereas the
+ioctl event interface is not.

-There are two functions currently for device-mapper events. The first function
-listed creates the event and the second function sends the event(s).
+There are five functions DM targets should use.

-void dm_path_uevent(enum dm_uevent_type event_type, struct dm_target *ti,
- const char *path, unsigned nr_valid_paths)
+struct dm_uevent *dm_build_uevent(struct mapped_device *md,
+ struct dm_target *ti,
+ enum kobject_action action,
+ const char *dm_action)
+Construct a dm uevent with default DM variables attached(DM_TARGET,
+int add_uevent_var(struct kobj_uevent_env *env, const char *format, ...)
+Optionally add event-specific data to the generated uevent. e.g. dm-mpath's
+PATH_FAILED and PATH_REINSTATED uevents add path and number-of-remaining-paths
+void dm_uevent_add(struct mapped_device *md, struct list_head *elist)
+Hand off the uevent to the device's list of pending events.
+void dm_uevent_free(struct dm_uevent *event)
+Something went wrong, free the uevent instead of queueing it.
+void dm_table_event(struct dm_table *t)
+Triggers sending of queued uevents as well as waking up processes waiting on
+the ioctl.
+The device-mapper uevent code also supplies three functions for device-mapper core
+to call:
+int dm_uevent_init(void)
+void dm_uevent_exit(void)
+Setup and teardown.

void dm_send_uevents(struct list_head *events, struct kobject *kobj)

+Actually send the uevents (called indirectly from dm_table_event, above).

The variables added to the uevent environment are:

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