init: Wait for /dev/hvc1 during ARCVM first-stage mount

This commit introduces a function to allow ARC-specific logic during
first-stage mount by checking for the existence of an indicator file
at the path "/is_arcvm".

ARC uses the virtio-console device `hvc1` to pass byte data to Android
before second-stage init. Ensure that /dev/hvc1 is initialized before
ARCVM continues booting, but allow other devices to bypass this device
initialization.

Bug: 325538592
Test: boot ARC, ensure /dev/hvc1 can be read during PropertyInit
Change-Id: Ic258b7b004b59da462f4990131a5c11fc94eca62

init/first_stage_mount.cpp

@@ -305,6 +305,11 @@ bool FirstStageMountVBootV2::InitDevices() {
             return false;
         }
     }
+
+    if (IsArcvm() && !block_dev_init_.InitHvcDevice("hvc1")) {
+        return false;
+    }
+
     return true;
 }
 

init/selinux.cpp

@@ -474,6 +474,8 @@ void SelinuxRestoreContext() {
     RestoreconIfExists(SnapshotManager::GetGlobalRollbackIndicatorPath().c_str(), 0);
     RestoreconIfExists("/metadata/gsi",
                        SELINUX_ANDROID_RESTORECON_RECURSE | SELINUX_ANDROID_RESTORECON_SKIP_SEHASH);
+
+    RestoreconIfExists("/dev/hvc1", 0);
 }
 
 int SelinuxKlogCallback(int type, const char* fmt, ...) {

init/util.h

@@ -18,6 +18,7 @@
 
 #include <sys/stat.h>
 #include <sys/types.h>
+#include <sys/unistd.h>
 
 #include <chrono>
 #include <functional>
@@ -108,6 +109,10 @@ inline constexpr bool IsMicrodroid() {
 #endif
 }
 
+inline bool IsArcvm() {
+    return !access("/is_arcvm", F_OK);
+}
+
 bool Has32BitAbi();
 
 std::string GetApexNameFromFileName(const std::string& path);