fs_mgr_fstab: translate reserve_root to reserved_size in fsmgr

Without this patch, fstab should decribe reserve_root=[# of 4KB blocks] in
f2fs mount option as well as reserved_size=[KB] in fsmgr flag to notify it
to framework.
With this patch, it should be just fine to use reserve_root=[# of 4KB blocks]
in fstab.

Bug: 135003600
Test: checked vold.has_reserved
Change-Id: Iab75f7da9792ad205a6c4d2d0f1eba8c16a5266a
Signed-off-by: Jaegeuk Kim <jaegeuk@google.com>

fs_mgr/fs_mgr_fstab.cpp

@@ -171,6 +171,18 @@ void ParseMountFlags(const std::string& flags, FstabEntry* entry) {
                 fs_options.append(",");  // appends a comma if not the first
             }
             fs_options.append(flag);
+
+            if (entry->fs_type == "f2fs" && StartsWith(flag, "reserve_root=")) {
+                std::string arg;
+                if (auto equal_sign = flag.find('='); equal_sign != std::string::npos) {
+                    arg = flag.substr(equal_sign + 1);
+                }
+                if (!ParseInt(arg, &entry->reserved_size)) {
+                    LWARNING << "Warning: reserve_root= flag malformed: " << arg;
+                } else {
+                    entry->reserved_size <<= 12;
+                }
+            }
         }
     }
     entry->fs_options = std::move(fs_options);