Added state snapshot support for QemuD.
With this patch, both modem and sensor functionality are correctly
restored when a state snapshot is loaded. This was not the case
previously because communication with either of these services is
done using the qemud daemon, which did not support snapshots.
The boot-properties and charpipe services have no specific save/load
functionality yet, since the framework itself should be reviewed
first. Adding support for bootproperties should not be difficult
though, and charpipe may not need it.
For a description of the high-level process for saving and loading,
consult section IV "State snapshots" in docs/ANDROID-QEMUD.TXT.
Change-Id: I5b06d88b911ca096e78060163174904c48a01c66
diff --git a/docs/ANDROID-QEMUD.TXT b/docs/ANDROID-QEMUD.TXT
index 1364553..7841399 100644
--- a/docs/ANDROID-QEMUD.TXT
+++ b/docs/ANDROID-QEMUD.TXT
@@ -249,3 +249,27 @@
The current implementation moves any service-specific code to the emulator,
only uses a single socket and allows concurrent clients for a all services.
+
+
+IV. State snapshots:
+--------------------
+
+Support for snapshots relies on the symmetric qemud_*_save and qemud_*_load
+functions which save the state of the various Qemud* structs defined in
+android/hw-qemud.c. The high-level process is as follows.
+
+When a snapshot is made, the names and configurations of all services are
+saved. Services can register a custom callback, which is invoked at this point
+to allow saving of service-specific state. Next, clients are saved following
+the same pattern. We save the channel id and the name of service they are
+registered to, then invoke a client-specific callback.
+
+When a snapshot is restored, the first step is to check whether all services
+that were present when the snapshot was made are available. There is currently
+no functionality to start start missing services, so loading fails if a service
+is not present. If all services are present, callbacks are used to restore
+service-specific state.
+
+Next, all active clients are shut down. Information from the snapshot is used
+to start new clients for the services and channels as they were when the
+snapshot was made. This completes the restore process.