MDEV-33671: Remove hardcoded open-files-limit in safe_process.cc

The fixed limit of 1024 open files was preventing proper concurrency
testing in MTR. This commit removes the hardcoded value and adds a new
option to control the limit when running tests: --open-files-limit=X.

The default is still 1024, but it can now be changed when needed,
making it easier to test scenarios that require different number of
open file descriptors at the same time e.g: partition_notwin.test

Documentation is added to mtr's help file as well.

Signed-off-by: Vicențiu Ciorbaru <vicentiu@mariadb.org>

mysql-test/lib/My/SafeProcess.pm

@@ -138,6 +138,7 @@ sub new {
   my $error    = delete($opts{'error'});
   my $verbose  = delete($opts{'verbose'}) || $::opt_verbose;
   my $nocore   = delete($opts{'nocore'});
+  my $open_files_limit = delete($opts{'open_files_limit'});
   my $host     = delete($opts{'host'});
   my $shutdown = delete($opts{'shutdown'});
   my $user_data= delete($opts{'user_data'});
@@ -161,6 +162,8 @@ sub new {
   push(@safe_args, "--verbose") if $verbose > 0;
   push(@safe_args, "--nocore") if $nocore;
 
+  push(@safe_args, "--open-files-limit=$open_files_limit") if $open_files_limit;
+
   # Point the safe_process at the right parent if running on cygwin
   push(@safe_args, "--parent-pid=".Cygwin::pid_to_winpid($$)) if IS_CYGWIN;
 

mysql-test/lib/My/SafeProcess/safe_process.cc

@@ -220,6 +220,7 @@ int main(int argc, char* const argv[] )
   pid_t own_pid= getpid();
   pid_t parent_pid= getppid();
   bool nocore = false;
+  int open_files_limit = 1024;
   struct sigaction sa,sa_abort;
 
   sa.sa_handler= handle_signal;
@@ -268,7 +269,14 @@ int main(int argc, char* const argv[] )
       }
       else if ( strncmp (arg, "--env ", 6) == 0 )
       {
-	putenv(strdup(arg+6));
+        putenv(strdup(arg+6));
+      }
+      else if ( strncmp(arg, "--open-files-limit=", 19) == 0 )
+      {
+        const char* start = arg + 19;
+        open_files_limit = atoi(start);
+        if (open_files_limit <= 0)
+          die("Invalid value '%s' passed to --open-files-limit", start);
       }
       else
         die("Unknown option: %s", arg);
@@ -318,11 +326,8 @@ int main(int argc, char* const argv[] )
     if (nocore)
       setlimit(RLIMIT_CORE, 0, 0);
 
-    /*
+    // Set open files limit 
-      mysqld defaults depend on that. make test results stable and independent
+    setlimit(RLIMIT_NOFILE, open_files_limit, open_files_limit);
-      from the environment
-    */
-    setlimit(RLIMIT_NOFILE, 1024, 1024);
 
     // Signal that child is ready
     buf= 37;

mysql-test/mariadb-test-run.pl

@@ -130,6 +130,8 @@ our $path_language;
 our $path_current_testlog;
 our $path_testlog;
 
+our $opt_open_files_limit;
+
 our $default_vardir;
 our $opt_vardir;                # Path to use for var/ dir
 our $plugindir;
@@ -1277,6 +1279,7 @@ sub command_line_setup {
 	     'list-options'             => \$opt_list_options,
              'skip-test-list=s'         => \@opt_skip_test_list,
              'xml-report=s'             => \$opt_xml_report,
+             'open-files-limit=i',      => \$opt_open_files_limit,
 
              My::Debugger::options(),
              My::CoreDump::options(),
@@ -5767,6 +5770,7 @@ sub start_mysqltest ($) {
      append        => 1,
      error         => $path_current_testlog,
      verbose       => $opt_verbose,
+     open_files_limit => $opt_open_files_limit,
     );
   mtr_verbose("Started $proc");
   return $proc;
@@ -6065,6 +6069,8 @@ Misc options
   timediff              With --timestamp, also print time passed since
                         *previous* test started
   max-connections=N     Max number of open connection to server in mysqltest
+  open-files-limit=N    Max number of open files allowed for any of the children
+                        of my_safe_process. Default is 1024.
   report-times          Report how much time has been spent on different
                         phases of test execution.
   stress=ARGS           Run stress test, providing options to