base: extend emergency dataspace size

The emergency dataspace is used to accommodate the corner case where
a signal context capability is created while issuing the first
resource request. Normally, the attempt to upgrade the signal-session
quota under such a constrained situation would fail. By freeing the
emergency dataspace in this situation, we regain enough quota to
upgrade the signal session.

This is a follow up commit for "base: Raise RAM quota of signal session
to 16K" and fixes the resource_request test on 64-bit platforms.

repos/base-linux/src/base/env/platform_env.h

@@ -412,7 +412,7 @@ namespace Genode {
 			 *
 			 * See the comment of '_fallback_sig_cap()' in 'env/env.cc'.
 			 */
-			constexpr static size_t  _emergency_ram_size() { return 4*1024; }
+			constexpr static size_t  _emergency_ram_size() { return 8*1024; }
 			Ram_dataspace_capability _emergency_ram_ds;
 
 

repos/base/src/base/env/platform_env.h

@@ -97,7 +97,7 @@ class Genode::Platform_env : public Genode::Env, public Emergency_ram_reserve
 		 *
 		 * See the comment of '_fallback_sig_cap()' in 'env/env.cc'.
 		 */
-		constexpr static size_t  _emergency_ram_size() { return 4*1024; }
+		constexpr static size_t  _emergency_ram_size() { return 8*1024; }
 		Ram_dataspace_capability _emergency_ram_ds;
 
 	public:

repos/base/src/base/signal/signal.cc

@@ -230,6 +230,7 @@ void Signal_context::submit(unsigned num)
 
 Signal_connection * Signal_transmitter::connection() { return signal_connection(); }
 
+
 /*********************
  ** Signal receiver **
  *********************/

repos/os/src/test/resource_request/main.cc

@@ -67,6 +67,9 @@ int main(int argc, char **argv)
 	 * successively upgrade the session. At one point, we will run out of our
 	 * initial quota. Now, before we can issue another upgrade, we first need
 	 * to request additional resources.
+	 *
+	 * Note that the construction of the signal receiver will consume a part
+	 * of the quota we preserved as 'KEEP_QUOTA'.
 	 */
 	printf("\n-- draining signal session --\n");
 	{