Sync PSU images on service startup

On service startup, it shall check the PSU images, find a latest
version, and update to the PSUs that are not with this version.

Tested: With dummy image and service, test on Witherspoon with 2
        different running PSU software:
* When startup without stored image, the serive tries to update an older
PSU but it does not have PSU image, so it's skipped with below journal
log:
    Automatically update PSU
    No image for the activation, skipped
* When startup with an older image stored in BMC, it behaves the same as
above.
* When startup with a new image stored in BMC, it updates the PSUs, with
below example journal log:
    Automatically update PSU
    Starting Update PSU
    /xyz/openbmc_project/inventory/system/chassis/motherboard/powersupply0
    /var/lib/obmc/psu/2B1D...
    Started Update PSU
    /xyz/openbmc_project/inventory/system/chassis/motherboard/powersupply0
    /var/lib/obmc/psu/2B1D.
    Starting Update PSU
    /xyz/openbmc_project/inventory/system/chassis/motherboard/powersupply1
    /var/lib/obmc/psu/2B1D...
    Started Update PSU
    /xyz/openbmc_project/inventory/system/chassis/motherboard/powersupply1
    /var/lib/obmc/psu/2B1D.

Signed-off-by: Lei YU <mine260309@gmail.com>
Change-Id: I6d676c5a4441685fb2b5920455f439c00f6097af
diff --git a/src/item_updater.cpp b/src/item_updater.cpp
index 13e6bf4..acbc943 100644
--- a/src/item_updater.cpp
+++ b/src/item_updater.cpp
@@ -435,6 +435,40 @@
     return versionId;
 }
 
+void ItemUpdater::syncToLatestImage()
+{
+    auto latestVersionId = getLatestVersionId();
+    if (!latestVersionId)
+    {
+        return;
+    }
+    const auto& it = activations.find(*latestVersionId);
+    assert(it != activations.end());
+    const auto& activation = it->second;
+    const auto& assocs = activation->associations();
+
+    auto paths = utils::getPSUInventoryPath(bus);
+    for (const auto& p : paths)
+    {
+        // As long as there is a PSU is not associated with the latest image,
+        // run the activation so that all PSUs are running the same latest
+        // image.
+        if (!utils::isAssociated(p, assocs))
+        {
+            log<level::INFO>("Automatically update PSU",
+                             entry("VERSION_ID=%s", latestVersionId->c_str()));
+            invokeActivation(activation);
+            break;
+        }
+    }
+}
+
+void ItemUpdater::invokeActivation(
+    const std::unique_ptr<Activation>& activation)
+{
+    activation->requestedActivation(Activation::RequestedActivations::Active);
+}
+
 } // namespace updater
 } // namespace software
 } // namespace phosphor