liblp: Add helpers for finding partitions and partition sizes.

These tend to get manually, so let's promote to actual helpers.

Bug: 134536978
Test: liblp_test gtest
Change-Id: Ifb79c8d6f247cc3f9635bf6adfd1c99907340002

fastboot/device/commands.cpp

@@ -94,7 +94,7 @@ bool GetVarHandler(FastbootDevice* device, const std::vector<std::string>& args)
             {FB_VAR_HAS_SLOT, {GetHasSlot, GetAllPartitionArgsNoSlot}},
             {FB_VAR_SLOT_SUCCESSFUL, {GetSlotSuccessful, nullptr}},
             {FB_VAR_SLOT_UNBOOTABLE, {GetSlotUnbootable, nullptr}},
-            {FB_VAR_PARTITION_SIZE, {GetPartitionSize, GetAllPartitionArgsWithSlot}},
+            {FB_VAR_PARTITION_SIZE, {::GetPartitionSize, GetAllPartitionArgsWithSlot}},
             {FB_VAR_PARTITION_TYPE, {GetPartitionType, GetAllPartitionArgsWithSlot}},
             {FB_VAR_IS_LOGICAL, {GetPartitionIsLogical, GetAllPartitionArgsWithSlot}},
             {FB_VAR_IS_USERSPACE, {GetIsUserspace, nullptr}},

fs_mgr/liblp/builder_test.cpp

@@ -106,6 +106,13 @@ TEST_F(BuilderTest, ResizePartition) {
     EXPECT_EQ(extent->num_sectors(), 32768 / LP_SECTOR_SIZE);
     EXPECT_EQ(extent->physical_sector(), 32);
 
+    auto exported = builder->Export();
+    ASSERT_NE(exported, nullptr);
+    ASSERT_EQ(FindPartition(*exported.get(), "not found"), nullptr);
+    auto entry = FindPartition(*exported.get(), "system");
+    ASSERT_NE(entry, nullptr);
+    ASSERT_EQ(GetPartitionSize(*exported.get(), *entry), 32768);
+
     // Test shrinking to 0.
     builder->ResizePartition(system, 0);
     EXPECT_EQ(system->size(), 0);

fs_mgr/liblp/include/liblp/liblp.h

@@ -107,6 +107,10 @@ uint32_t SlotNumberForSlotSuffix(const std::string& suffix);
 std::string SlotSuffixForSlotNumber(uint32_t slot_number);
 std::string GetPartitionSlotSuffix(const std::string& partition_name);
 
+// Helpers for common functions.
+const LpMetadataPartition* FindPartition(const LpMetadata& metadata, const std::string& name);
+uint64_t GetPartitionSize(const LpMetadata& metadata, const LpMetadataPartition& partition);
+
 }  // namespace fs_mgr
 }  // namespace android
 

fs_mgr/liblp/utility.cpp

@@ -135,6 +135,24 @@ std::vector<std::string> GetBlockDevicePartitionNames(const LpMetadata& metadata
     return list;
 }
 
+const LpMetadataPartition* FindPartition(const LpMetadata& metadata, const std::string& name) {
+    for (const auto& partition : metadata.partitions) {
+        if (GetPartitionName(partition) == name) {
+            return &partition;
+        }
+    }
+    return nullptr;
+}
+
+uint64_t GetPartitionSize(const LpMetadata& metadata, const LpMetadataPartition& partition) {
+    uint64_t total_size = 0;
+    for (uint32_t i = 0; i < partition.num_extents; i++) {
+        const auto& extent = metadata.extents[partition.first_extent_index + i];
+        total_size += extent.num_sectors * LP_SECTOR_SIZE;
+    }
+    return total_size;
+}
+
 std::string GetPartitionSlotSuffix(const std::string& partition_name) {
     if (partition_name.size() <= 2) {
         return "";