Set metadata cipher in fstab

Bug: 147814592
Test: Cuttlefish can use adiantum
Change-Id: I9207ffcdb74dcd36c8b2534b51233a3f8e80dc0b

fs_mgr/fs_mgr_fstab.cpp

@@ -277,6 +277,9 @@ void ParseFsMgrFlags(const std::string& flags, FstabEntry* entry) {
         } else if (StartsWith(flag, "keydirectory=")) {
             // The metadata flag is followed by an = and the directory for the keys.
             entry->metadata_key_dir = arg;
+        } else if (StartsWith(flag, "metadata_cipher=")) {
+            // Specify the cipher to use for metadata encryption
+            entry->metadata_cipher = arg;
         } else if (StartsWith(flag, "sysfs_path=")) {
             // The path to trigger device gc by idle-maint of vold.
             entry->sysfs_path = arg;

fs_mgr/include_fstab/fstab/fstab.h

@@ -38,6 +38,7 @@ struct FstabEntry {
     std::string fs_options;
     std::string key_loc;
     std::string metadata_key_dir;
+    std::string metadata_cipher;
     off64_t length = 0;
     std::string label;
     int partnum = -1;

fs_mgr/tests/fs_mgr_test.cpp

@@ -895,6 +895,23 @@ source none0       swap   defaults      keydirectory=/dir/key
     EXPECT_EQ("/dir/key", entry->metadata_key_dir);
 }
 
+TEST(fs_mgr, ReadFstabFromFile_FsMgrOptions_MetadataCipher) {
+    TemporaryFile tf;
+    ASSERT_TRUE(tf.fd != -1);
+    std::string fstab_contents = R"fs(
+source none0       swap   defaults      keydirectory=/dir/key,metadata_cipher=adiantum
+)fs";
+
+    ASSERT_TRUE(android::base::WriteStringToFile(fstab_contents, tf.path));
+
+    Fstab fstab;
+    EXPECT_TRUE(ReadFstabFromFile(tf.path, &fstab));
+    ASSERT_EQ(1U, fstab.size());
+
+    auto entry = fstab.begin();
+    EXPECT_EQ("adiantum", entry->metadata_cipher);
+}
+
 TEST(fs_mgr, ReadFstabFromFile_FsMgrOptions_SysfsPath) {
     TemporaryFile tf;
     ASSERT_TRUE(tf.fd != -1);