Merge "liblp: Force 10.0 metadata on downgrade to Q." into rvc-dev

fs_mgr/liblp/builder.cpp

@@ -204,11 +204,18 @@ std::unique_ptr<MetadataBuilder> MetadataBuilder::NewForUpdate(const IPartitionO
         }
     }
 
-    if (IPropertyFetcher::GetInstance()->GetBoolProperty("ro.virtual_ab.enabled", false) &&
-        !always_keep_source_slot) {
-        if (!UpdateMetadataForInPlaceSnapshot(metadata.get(), source_slot_number,
-                                              target_slot_number)) {
-            return nullptr;
+    if (IPropertyFetcher::GetInstance()->GetBoolProperty("ro.virtual_ab.enabled", false)) {
+        if (always_keep_source_slot) {
+            // always_keep_source_slot implies the target build does not support snapshots.
+            // Clear unsupported attributes.
+            SetMetadataHeaderV0(metadata.get());
+        } else {
+            // !always_keep_source_slot implies the target build supports snapshots. Do snapshot
+            // updates.
+            if (!UpdateMetadataForInPlaceSnapshot(metadata.get(), source_slot_number,
+                                                  target_slot_number)) {
+                return nullptr;
+            }
         }
     }
 

fs_mgr/liblp/include/liblp/builder.h

@@ -209,8 +209,10 @@ class MetadataBuilder {
     // metadata may not have the target slot's devices listed yet, in which
     // case, it is automatically upgraded to include all available block
     // devices.
-    // If |always_keep_source_slot| is set, on a Virtual A/B device, source slot
-    // partitions are kept. This is useful when applying a downgrade package.
+    // If |always_keep_source_slot| is set, on a Virtual A/B device
+    // - source slot partitions are kept.
+    // - UPDATED flag is cleared.
+    // This is useful when applying a downgrade package.
     static std::unique_ptr<MetadataBuilder> NewForUpdate(const IPartitionOpener& opener,
                                                          const std::string& source_partition,
                                                          uint32_t source_slot_number,

fs_mgr/liblp/utility.cpp

@@ -15,6 +15,7 @@
  */
 
 #include <fcntl.h>
+#include <inttypes.h>
 #include <stdint.h>
 #include <sys/stat.h>
 #include <unistd.h>
@@ -29,6 +30,7 @@
 #include <vector>
 
 #include <android-base/file.h>
+#include <android-base/stringprintf.h>
 #include <ext4_utils/ext4_utils.h>
 #include <openssl/sha.h>
 
@@ -285,5 +287,42 @@ bool UpdateMetadataForInPlaceSnapshot(LpMetadata* metadata, uint32_t source_slot
     return true;
 }
 
+inline std::string ToHexString(uint64_t value) {
+    return android::base::StringPrintf("0x%" PRIx64, value);
+}
+
+void SetMetadataHeaderV0(LpMetadata* metadata) {
+    if (metadata->header.minor_version <= LP_METADATA_MINOR_VERSION_MIN) {
+        return;
+    }
+    LINFO << "Forcefully setting metadata header version " << LP_METADATA_MAJOR_VERSION << "."
+          << metadata->header.minor_version << " to " << LP_METADATA_MAJOR_VERSION << "."
+          << LP_METADATA_MINOR_VERSION_MIN;
+    metadata->header.minor_version = LP_METADATA_MINOR_VERSION_MIN;
+    metadata->header.header_size = sizeof(LpMetadataHeaderV1_0);
+
+    // Retrofit Virtual A/B devices should have version 10.1, so flags shouldn't be set.
+    // Warn if this is the case, but zero it out anyways.
+    if (metadata->header.flags) {
+        LWARN << "Zeroing unexpected flags: " << ToHexString(metadata->header.flags);
+    }
+
+    // Zero out all fields beyond LpMetadataHeaderV0.
+    static_assert(sizeof(metadata->header) > sizeof(LpMetadataHeaderV1_0));
+    memset(reinterpret_cast<uint8_t*>(&metadata->header) + sizeof(LpMetadataHeaderV1_0), 0,
+           sizeof(metadata->header) - sizeof(LpMetadataHeaderV1_0));
+
+    // Clear partition attributes unknown to V0.
+    // On retrofit Virtual A/B devices, UPDATED flag may be set, so only log info here.
+    for (auto& partition : metadata->partitions) {
+        if (partition.attributes & ~LP_PARTITION_ATTRIBUTE_MASK_V0) {
+            LINFO << "Clearing " << GetPartitionName(partition)
+                  << " partition attribute: " << ToHexString(partition.attributes);
+        }
+
+        partition.attributes &= LP_PARTITION_ATTRIBUTE_MASK_V0;
+    }
+}
+
 }  // namespace fs_mgr
 }  // namespace android

fs_mgr/liblp/utility.h

@@ -103,6 +103,10 @@ bool SetBlockReadonly(int fd, bool readonly);
 bool UpdateMetadataForInPlaceSnapshot(LpMetadata* metadata, uint32_t source_slot_number,
                                       uint32_t target_slot_number);
 
+// Forcefully set metadata header version to 1.0, clearing any incompatible flags and attributes
+// so that when downgrading to a build with liblp V0, the device still boots.
+void SetMetadataHeaderV0(LpMetadata* metadata);
+
 }  // namespace fs_mgr
 }  // namespace android