common/config: Add methods to return the default value of a config option

Add wrapper method "get_val_default()" to the ConfigProxy class that takes
the config option key to search. This method in-turn calls another method
with the same name added to md_config_t class that does the actual work of
searching for the config option. If the option is valid, _get_val_default()
is used to get the default value. Otherwise, the wrapper method returns
std::nullopt.

Fixes: https://tracker.ceph.com/issues/51464
Signed-off-by: Sridhar Seshasayee <sseshasa@redhat.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/src/common/config.cc b/src/common/config.cc
index a58d9d9e1f2..c8101587b71 100644
--- a/src/common/config.cc
+++ b/src/common/config.cc
@@ -1024,6 +1024,16 @@ void md_config_t::get_config_bl(
   }
 }
 
+std::optional<std::string> md_config_t::get_val_default(std::string_view key)
+{
+  std::string val;
+  const Option *opt = find_option(key);
+  if (opt && (conf_stringify(_get_val_default(*opt), &val) == 0)) {
+    return std::make_optional(std::move(val));
+  }
+  return std::nullopt;
+}
+
 int md_config_t::get_val(const ConfigValues& values,
 			 const std::string_view key, char **buf, int len) const
 {