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Documentation/device-mapper/dm-uevent.txt 2.59 KB
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7a8c3d3b9   Mike Anderson   dm: uevent genera... 
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  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
  the event avoiding the need to query the state of the device-mapper device after
  the event is received.
  
  There are two functions currently for device-mapper events.  The first function
  listed creates the event and the second function sends the event(s).
  
  void dm_path_uevent(enum dm_uevent_type event_type, struct dm_target *ti,
                      const char *path, unsigned nr_valid_paths)
  
  void dm_send_uevents(struct list_head *events, struct kobject *kobj)
  
  
  The variables added to the uevent environment are:
  
  Variable Name: DM_TARGET
  Uevent Action(s): KOBJ_CHANGE
  Type: string
  Description:
  Value: Name of device-mapper target that generated the event.
  
  Variable Name: DM_ACTION
  Uevent Action(s): KOBJ_CHANGE
  Type: string
  Description:
  Value: Device-mapper specific action that caused the uevent action.
  	PATH_FAILED - A path has failed.
  	PATH_REINSTATED - A path has been reinstated.
  
  Variable Name: DM_SEQNUM
  Uevent Action(s): KOBJ_CHANGE
  Type: unsigned integer
  Description: A sequence number for this specific device-mapper device.
  Value: Valid unsigned integer range.
  
  Variable Name: DM_PATH
  Uevent Action(s): KOBJ_CHANGE
  Type: string
  Description: Major and minor number of the path device pertaining to this
  event.
  Value: Path name in the form of "Major:Minor"
  
  Variable Name: DM_NR_VALID_PATHS
  Uevent Action(s): KOBJ_CHANGE
  Type: unsigned integer
  Description:
  Value: Valid unsigned integer range.
  
  Variable Name: DM_NAME
  Uevent Action(s): KOBJ_CHANGE
  Type: string
  Description: Name of the device-mapper device.
  Value: Name
  
  Variable Name: DM_UUID
  Uevent Action(s): KOBJ_CHANGE
  Type: string
  Description: UUID of the device-mapper device.
  Value: UUID. (Empty string if there isn't one.)
  
  An example of the uevents generated as captured by udevmonitor is shown
  below.
  
  1.) Path failure.
  UEVENT[1192521009.711215] change@/block/dm-3
  ACTION=change
  DEVPATH=/block/dm-3
  SUBSYSTEM=block
  DM_TARGET=multipath
  DM_ACTION=PATH_FAILED
  DM_SEQNUM=1
  DM_PATH=8:32
  DM_NR_VALID_PATHS=0
  DM_NAME=mpath2
  DM_UUID=mpath-35333333000002328
  MINOR=3
  MAJOR=253
  SEQNUM=1130
  
  2.) Path reinstate.
  UEVENT[1192521132.989927] change@/block/dm-3
  ACTION=change
  DEVPATH=/block/dm-3
  SUBSYSTEM=block
  DM_TARGET=multipath
  DM_ACTION=PATH_REINSTATED
  DM_SEQNUM=2
  DM_PATH=8:32
  DM_NR_VALID_PATHS=1
  DM_NAME=mpath2
  DM_UUID=mpath-35333333000002328
  MINOR=3
  MAJOR=253
  SEQNUM=1131