Bug#35779802 - empty vio->signal_mask in the x plugin causes MySQL cannot handle signal

Description
===========
VIO on POSIX systems uses PPOLL to do the IO. The VIO has a configuration
option that allows overwrting  the signal mask while doing the IO call.
When sending SIGTERM (graceful shutdown) to the MySQL Server,
the signal is handled by default signal handler (not by mysqld-signal handler).
This leads to application forced shutdown (kill).

Fix
===
Initialize VIO structure with correct signal mask, that is used
with ppoll.

Change-Id: I5f7de6d928af282f9217414a92ea1e268fb5e69c

Author: lkotula

plugin/x/src/mysql_variables.cc

@@ -41,4 +41,6 @@ const CHARSET_INFO *get_default_charset() {
   return &my_charset_utf8mb4_0900_ai_ci;
 }
 
+sigset_t get_mysqld_signal_mask() { return mysqld_signal_mask; }
+
 }  // namespace mysqld

plugin/x/src/mysql_variables.h

@@ -25,6 +25,9 @@
 #ifndef PLUGIN_X_SRC_MYSQL_VARIABLES_H_
 #define PLUGIN_X_SRC_MYSQL_VARIABLES_H_
 
+#include <signal.h>
+#include "my_inttypes.h"  // NOLINT(build/include_subdir)
+
 struct CHARSET_INFO;
 
 namespace mysqld {
@@ -35,6 +38,7 @@ bool is_terminating();
 bool get_initialize();
 const char *get_my_localhost();
 const CHARSET_INFO *get_default_charset();
+sigset_t get_mysqld_signal_mask();
 
 }  // namespace mysqld
 

plugin/x/src/ngs/socket_events.cc

@@ -31,6 +31,7 @@
 #include "violite.h"  // NOLINT(build/include_subdir)
 
 #include "plugin/x/src/interface/connection_acceptor.h"
+#include "plugin/x/src/mysql_variables.h"
 #include "plugin/x/src/ngs/memory.h"
 #include "plugin/x/src/ngs/socket_events.h"
 #include "plugin/x/src/operations_factory.h"
@@ -93,6 +94,10 @@ class Connection_acceptor_socket : public xpl::iface::Connection_acceptor {
                                is_tcpip ? VIO_TYPE_TCPIP : VIO_TYPE_SOCKET, 0);
     if (!vio) throw std::bad_alloc();
 
+#ifdef USE_PPOLL_IN_VIO
+    vio->signal_mask = mysqld::get_mysqld_signal_mask();
+#endif
+
     // enable TCP_NODELAY
     vio_fastsend(vio);
     vio_keepalive(vio, true);