| A DT changeset is a method which allows one to apply changes |
| in the live tree in such a way that either the full set of changes |
| will be applied, or none of them will be. If an error occurs partway |
| through applying the changeset, then the tree will be rolled back to the |
| previous state. A changeset can also be removed after it has been |
| applied. |
| |
| When a changeset is applied, all of the changes get applied to the tree |
| at once before emitting OF_RECONFIG notifiers. This is so that the |
| receiver sees a complete and consistent state of the tree when it |
| receives the notifier. |
| |
| The sequence of a changeset is as follows. |
| |
| 1. of_changeset_init() - initializes a changeset |
| |
| 2. A number of DT tree change calls, of_changeset_attach_node(), |
| of_changeset_detach_node(), of_changeset_add_property(), |
| of_changeset_remove_property, of_changeset_update_property() to prepare |
| a set of changes. No changes to the active tree are made at this point. |
| All the change operations are recorded in the of_changeset 'entries' |
| list. |
| |
| 3. mutex_lock(of_mutex) - starts a changeset; The global of_mutex |
| ensures there can only be one editor at a time. |
| |
| 4. of_changeset_apply() - Apply the changes to the tree. Either the |
| entire changeset will get applied, or if there is an error the tree will |
| be restored to the previous state |
| |
| 5. mutex_unlock(of_mutex) - All operations complete, release the mutex |
| |
| If a successfully applied changeset needs to be removed, it can be done |
| with the following sequence. |
| |
| 1. mutex_lock(of_mutex) |
| |
| 2. of_changeset_revert() |
| |
| 3. mutex_unlock(of_mutex) |
