UeventDetails

Ueventd Details

ueventd is a queue daemon. The task of this server is to process events from the queue. Each event in its queue is processed one by one in the order of arrival, but several queues can be processed in parallel.

Queues are implemented on the filesystem. All incoming events are placed as:

/.initrd/uevent/queues/<QUEUE>/<EVENT>

Events come to this directory all the time. As soon as the server receives a inotify event that something appeared in the directory, it moves all files from the queue directory to:

/.initrd/uevent/events/<QUEUE>/<EVENT>

This is done to avoid a race condition between filters that add new events and handlers that process them slowly. All handlers are called one by one. Handlers come in two types:

1. /lib/uevent/handlers/[0-9][0-9][0-9]-<QUEUE>

This is an old version of handlers. Every handler is not called for every event, but sequentially. A handler can analyze all the events that have arrived and discard those if deemed necessary.

2. /lib/uevent/handlers/<QUEUE>/[0-9][0-9][0-9]-<HANDLER>

This is the new way to handle events. Handlers gets a directory with events as an argument. Just like the first case, the handler is not called for each event.

Processed events are prefixed with done. or deleted.

Uevent API

All filters and handlers should use /bin/uevent-sh-functions as the interface to events.

make_event is used to create a new event. It will not be published yet. The <QUEUE> is passed as an argument. This function returns the eventfile. You can write any necessary content to this file.

publish_event, release_event publishes an event. After that call, the event becomes available for processing.

done_event marks eventfile as processed. Processed events are prefixed with done. or deleted.

See also

• The article about runtime.