tree 5fcefe2ba8b78edf7c57cac7cf410180e6c3e6c3
parent b2b037d9f05eaef2c09fdd8ec905d75dc7ac2644
author Akilesh Kailash <akailash@google.com> 1694217675 -0700
committer Akilesh Kailash <akailash@google.com> 1694239785 -0700

libsnapshot_cow: Prepare device to boot from pre-created snapshots

Two new API's have been added:

1: BootFromSnapshotsWithoutSlotSwitch: This will create a new marker
which indicates first-stage init to mount the partitions off snapshots.

We need this marker as during boot, there are couple of places during
mounting snapshots wherein the marker is used. However, there is no
change in the existing I/O path related to OTA.

2: PrepareDeviceToBootWithoutSnapshot: This will delete the marker so
that subsequent reboot will not have the partitions mounted without the
snapshots.

VTS tests covers both these API's. Additionally, when these
markers are present, new OTA's cannot be installed. All these
are covered in VTS tests.

===========================================================

snapshotctl: General flow to apply and revert pre-created snapshots

1: To install the pre-created snapshots:

$snapshotctl map-snapshots <directory path containing snapshots patches>

Now the device is ready to boot from snapshots.

2: After device reboots, partitions are mounted off the snapshots. There
   is no snapshot-merge.

3: In order to go back to previous build:

$snapshotctl revert-snapshots

Now the device is ready to boot from base build.

4: After device reboots back to previous build, all the snapshot states
   and COW images are removed.

============================================

Additional commands:

To delete the pre-created snapshots:

$snapshotctl delete-snapshots

======================================

Tested it on Pixel 6 Pro between two builds which are ~24 hours apart.

1: Creating snapshots on a linux-host - ~4-6 seconds
2: Applying pre-created snapshots - ~10-15 seconds (includes intermediate
   transfer of patches to the device). This depends on the size of snapshot patches.
3: Device reboot - ~12-14 seconds.

Bug: 299011882
Test: 1: Apply pre-created snapshots
2: Reboot device: Verify new build
3: Apply OTA when partitions are mounted of snapshots and verify OTA
   fails.
3: Revert-snapshot and reboot.
4: Verify device goes back to base build.

Full OTA on Pixel. vts_libsnapshot_test

Change-Id: I36a72d973d8f70ae49773ebd45dd996fac22a4e3
Signed-off-by: Akilesh Kailash <akailash@google.com>