fs_mgr: add overlayfs handling for squashfs system filesystems

/cache/overlay directory in support of overlayfs mounts on userdebug
and eng devices.  Overlayfs in turn can be capable of supporting
adb remount for read-only or restricted-storage filesystems like
squashfs or right-sized (zero free space) system partitions
respectively.

Test: compile
Bug: 109821005
Bug: 110985612
Change-Id: I3ece03886db7cc97f864497cf93ec6c6c39bccd1
diff --git a/private/compat/26.0/26.0.ignore.cil b/private/compat/26.0/26.0.ignore.cil
index 056342b..ee202ba 100644
--- a/private/compat/26.0/26.0.ignore.cil
+++ b/private/compat/26.0/26.0.ignore.cil
@@ -84,6 +84,7 @@
     netd_stable_secret_prop
     network_watchlist_data_file
     network_watchlist_service
+    overlayfs_file
     package_native_service
     perfetto
     perfetto_exec
diff --git a/private/compat/27.0/27.0.ignore.cil b/private/compat/27.0/27.0.ignore.cil
index f99f9a7..b99de06 100644
--- a/private/compat/27.0/27.0.ignore.cil
+++ b/private/compat/27.0/27.0.ignore.cil
@@ -72,6 +72,7 @@
     mnt_vendor_file
     network_watchlist_data_file
     network_watchlist_service
+    overlayfs_file
     perfetto
     perfetto_exec
     perfetto_tmpfs
diff --git a/private/compat/28.0/28.0.ignore.cil b/private/compat/28.0/28.0.ignore.cil
index ad7faa3..7b16b96 100644
--- a/private/compat/28.0/28.0.ignore.cil
+++ b/private/compat/28.0/28.0.ignore.cil
@@ -9,6 +9,7 @@
     llkd_exec
     llkd_tmpfs
     mnt_product_file
+    overlayfs_file
     time_prop
     timedetector_service
     timezonedetector_service
diff --git a/private/file_contexts b/private/file_contexts
index 2087a36..6c75385 100644
--- a/private/file_contexts
+++ b/private/file_contexts
@@ -518,6 +518,11 @@
 # LocalTransport (backup) uses this subtree
 /cache/backup(/.*)?		u:object_r:cache_private_backup_file:s0
 
+#############################
+# Overlayfs support directories
+#
+/cache/overlay(/.*)?            u:object_r:overlayfs_file:s0
+
 /data/cache(/.*)?		u:object_r:cache_file:s0
 /data/cache/recovery(/.*)?	u:object_r:cache_recovery_file:s0
 # General backup/restore interchange with apps
diff --git a/private/file_contexts_overlayfs b/private/file_contexts_overlayfs
new file mode 100644
index 0000000..00902c2
--- /dev/null
+++ b/private/file_contexts_overlayfs
@@ -0,0 +1,6 @@
+#############################
+# Overlayfs support directories for userdebug/eng devices
+#
+/cache/overlay/(system|product)/upper       u:object_r:system_file:s0
+/cache/overlay/(vendor|odm)/upper           u:object_r:vendor_file:s0
+/cache/overlay/oem/upper                    u:object_r:vendor_file:s0
diff --git a/private/fs_use b/private/fs_use
index d351c36..1964348 100644
--- a/private/fs_use
+++ b/private/fs_use
@@ -8,6 +8,7 @@
 fs_use_xattr btrfs u:object_r:labeledfs:s0;
 fs_use_xattr f2fs u:object_r:labeledfs:s0;
 fs_use_xattr squashfs u:object_r:labeledfs:s0;
+fs_use_xattr overlay u:object_r:labeledfs:s0;
 fs_use_xattr erofs u:object_r:labeledfs:s0;
 
 # Label inodes from task label.