| Pantelis Antoniou | 201c910 | 2014-07-04 19:58:49 +0300 | [diff] [blame] | 1 | A DT changeset is a method which allows one to apply changes |
| 2 | in the live tree in such a way that either the full set of changes |
| 3 | will be applied, or none of them will be. If an error occurs partway |
| 4 | through applying the changeset, then the tree will be rolled back to the |
| 5 | previous state. A changeset can also be removed after it has been |
| 6 | applied. |
| 7 | |
| 8 | When a changeset is applied, all of the changes get applied to the tree |
| 9 | at once before emitting OF_RECONFIG notifiers. This is so that the |
| 10 | receiver sees a complete and consistent state of the tree when it |
| 11 | receives the notifier. |
| 12 | |
| 13 | The sequence of a changeset is as follows. |
| 14 | |
| 15 | 1. of_changeset_init() - initializes a changeset |
| 16 | |
| 17 | 2. A number of DT tree change calls, of_changeset_attach_node(), |
| 18 | of_changeset_detach_node(), of_changeset_add_property(), |
| 19 | of_changeset_remove_property, of_changeset_update_property() to prepare |
| 20 | a set of changes. No changes to the active tree are made at this point. |
| 21 | All the change operations are recorded in the of_changeset 'entries' |
| 22 | list. |
| 23 | |
| 24 | 3. mutex_lock(of_mutex) - starts a changeset; The global of_mutex |
| 25 | ensures there can only be one editor at a time. |
| 26 | |
| 27 | 4. of_changeset_apply() - Apply the changes to the tree. Either the |
| 28 | entire changeset will get applied, or if there is an error the tree will |
| 29 | be restored to the previous state |
| 30 | |
| 31 | 5. mutex_unlock(of_mutex) - All operations complete, release the mutex |
| 32 | |
| 33 | If a successfully applied changeset needs to be removed, it can be done |
| 34 | with the following sequence. |
| 35 | |
| 36 | 1. mutex_lock(of_mutex) |
| 37 | |
| 38 | 2. of_changeset_revert() |
| 39 | |
| 40 | 3. mutex_unlock(of_mutex) |