Add configurable RAM sell disable functionality

contracts/eosio.system/include/eosio.system/eosio.system.hpp

@@ -500,6 +500,10 @@ namespace eosiosystem {
       EOSLIB_SERIALIZE( refund_request, (owner)(request_time)(net_amount)(cpu_amount) )
    };
 
+   struct [[eosio::table, eosio::contract("eosio.system")]] ram_config {
+      bool disable_sellram = false;
+   };
+   typedef eosio::singleton< "ramconfig"_n, ram_config > ramconfig_singleton;
 
    struct [[eosio::table, eosio::contract("eosio.system")]] gifted_ram {
       name      giftee;
@@ -1427,6 +1431,17 @@ namespace eosiosystem {
          [[eosio::action]]
          action_return_sellram sellram( const name& account, int64_t bytes );
 
+         /**
+          * Set ram configuration action, configures RAM-related system settings.
+          * This action allows the system to enable or disable RAM selling functionality.
+          *
+          * @param disable_sellram - if true, disables the sellram action; if false, enables it.
+          *
+          * @pre Requires authority of the system contract itself.
+          */
+         [[eosio::action]]
+         void setramconfig(bool disable_sellram);
+
          /**
           * Gift ram action, which transfers `bytes` of ram from `gifter` (`from`) to `giftee` (`to`), 
           * with the characteristic that the transfered ram is encumbered, meaning it can only be 

contracts/eosio.system/src/delegate_bandwidth.cpp

@@ -106,6 +106,12 @@ namespace eosiosystem {
       require_recipient(receiver);
    }
 
+   void system_contract::setramconfig(bool disable_sellram) {
+      require_auth( get_self() );
+      ramconfig_singleton rc(get_self(), get_self().value);
+      rc.set(ram_config{.disable_sellram = disable_sellram}, get_self());
+   }
+
   /**
     *  The system contract now buys and sells RAM allocations at prevailing market prices.
     *  This may result in traders buying RAM today in anticipation of potential shortages
@@ -114,6 +120,11 @@ namespace eosiosystem {
     */
    action_return_sellram system_contract::sellram( const name& account, int64_t bytes ) {
       require_auth( account );
+      ramconfig_singleton rc(get_self(), get_self().value);
+      if (rc.exists()) {
+         check( rc.get().disable_sellram == false, "sellram is disabled");
+      }
+
       update_ram_supply();
       require_recipient(account);
       const int64_t ram_bytes = reduce_ram(account, bytes);