Implement File Descriptor Plugin

Made use of /proc filesystem to get list of open file descriptors.
This is implemented as a Information_Schema plugin table PROC_FDINFO.

plugin/proc_info/mysql-test/proc_info/fdinfo.result

+SHOW CREATE TABLE INFORMATION_SCHEMA.PROC_FDINFO;
+Table	Create Table
+PROC_FDINFO	CREATE TEMPORARY TABLE `PROC_FDINFO` (
+  `NAME` varchar(100) NOT NULL DEFAULT '',
+  `VALUE` varchar(512) DEFAULT NULL
+) ENGINE=MEMORY DEFAULT CHARSET=utf8
+SELECT PLUGIN_NAME, PLUGIN_VERSION, PLUGIN_TYPE, PLUGIN_AUTHOR, PLUGIN_DESCRIPTION, PLUGIN_LICENSE, PLUGIN_MATURITY FROM INFORMATION_SCHEMA.PLUGINS WHERE PLUGIN_NAME='proc_fdinfo';
+PLUGIN_NAME	PROC_FDINFO
+PLUGIN_VERSION	1.0
+PLUGIN_TYPE	INFORMATION SCHEMA
+PLUGIN_AUTHOR	
+PLUGIN_DESCRIPTION	Useful information from /proc
+PLUGIN_LICENSE	GPL
+PLUGIN_MATURITY	Experimental
+SELECT * FROM INFORMATION_SCHEMA.PROC_FDINFO
+WHERE NAME = '1' or NAME = '2' or NAME = '3'
+;
+NAME	VALUE
+1	MYSQLTEST_VARDIR_SOMETHING/log/mysqld.1.err
+2	MYSQLTEST_VARDIR_SOMETHING/log/mysqld.1.err
+3	MYSQLTEST_VARDIR_SOMETHING/mysqld.1/data/aria_log_control

plugin/proc_info/mysql-test/proc_info/fdinfo.test

+SHOW CREATE TABLE INFORMATION_SCHEMA.PROC_FDINFO;
+query_vertical SELECT PLUGIN_NAME, PLUGIN_VERSION, PLUGIN_TYPE, PLUGIN_AUTHOR, PLUGIN_DESCRIPTION, PLUGIN_LICENSE, PLUGIN_MATURITY FROM INFORMATION_SCHEMA.PLUGINS WHERE PLUGIN_NAME='proc_fdinfo';
+
+--replace_result $MYSQLTEST_VARDIR MYSQLTEST_VARDIR_SOMETHING
+SELECT * FROM INFORMATION_SCHEMA.PROC_FDINFO
+WHERE NAME = '1' or NAME = '2' or NAME = '3'
+;

plugin/proc_info/proc_info.cc

@@ -4,6 +4,9 @@
 #include <sql_class.h>
 #include <mysql/plugin.h>
 
+/* We'll use this to read directories */
+#include <dirent.h>
+
 
 static ST_FIELD_INFO meminfo_fields[]=
 {
@@ -12,6 +15,15 @@ static ST_FIELD_INFO meminfo_fields[]=
   { 0, 0, MYSQL_TYPE_STRING, 0, 0, 0, 0 }
 };
 
+static ST_FIELD_INFO fdinfo_fields[]=
+{
+	/* This can be number if we want to */
+  { "NAME", 100, MYSQL_TYPE_STRING, 0, 0, 0, SKIP_OPEN_TABLE },
+  { "VALUE", FN_REFLEN, MYSQL_TYPE_STRING, 0, MY_I_S_MAYBE_NULL, 0, SKIP_OPEN_TABLE },
+  { 0, 0, MYSQL_TYPE_STRING, 0, 0, 0, 0 }
+};
+
+
 
 static int meminfo_fill(MYSQL_THD thd, TABLE_LIST *tables, COND *cond)
 {
@@ -22,15 +34,18 @@ static int meminfo_fill(MYSQL_THD thd, TABLE_LIST *tables, COND *cond)
   int res;
 
 
+  /* Here we open /proc/meminfo to get info */
   if (!(fp= fopen("/proc/meminfo", "r")))
     return 1;
 
+  /* Read it in a loop, storing name and value */
   while ((res= fscanf(fp, "%[^:]: %lu kB\n", name, &value)) != EOF)
   {
     if (res != 2)
       continue;
     table->field[0]->store(name, strlen(name), system_charset_info);
     table->field[1]->store(value);
+    /* table->record is filled by field[x]->store() */
     if (schema_table_store_record(thd, table))
     {
       fclose(fp);
@@ -57,6 +72,75 @@ static int meminfo_init(void *p)
 static struct st_mysql_information_schema meminfo_plugin=
 { MYSQL_INFORMATION_SCHEMA_INTERFACE_VERSION };
 
+static struct st_mysql_information_schema fdinfo_plugin=
+{ MYSQL_INFORMATION_SCHEMA_INTERFACE_VERSION };
+
+static int fdinfo_fill(MYSQL_THD thd, TABLE_LIST *tables, COND *cond)
+{
+	int fd;
+
+	DIR *dir; /* from dirent.h */
+	struct dirent dirbuf, *result;
+	TABLE *table= tables->table;
+
+	char final_result[FN_REFLEN + 1];
+	int error= 0;
+
+	if ((fd= open("/proc/self/fd", O_DIRECTORY)) < 0)
+		return 1;
+
+	if ((dir= fdopendir(fd)) == NULL)
+	{
+		close(fd);
+		return 1;
+	}
+
+	while (readdir_r(dir, &dirbuf, &result) == 0 && result)
+	{
+		
+		if (result->d_name[0] == '.' /* for marko we'll do it later TODO */)
+			continue;
+		/* ASK  QUESTIONS IF THIS IS NOT CLEAR!! */
+		ssize_t len;
+		len= readlinkat(fd, result->d_name, final_result, sizeof(final_result)); 
+
+		table->field[0]->store(result->d_name, strlen(result->d_name), system_charset_info);
+		if (len < 0)
+		{
+			table->field[1]->set_null();
+		}
+		else
+		{
+			table->field[1]->store(final_result, len, system_charset_info);
+			table->field[1]->set_notnull(); /* Sets not-null bit */
+		}
+    if (schema_table_store_record(thd, table))
+    {
+			error= 1;
+			break; /* Error, Crash and burn?! */
+			/* clang-format  We should use this! */
+    }
+	}
+
+	close(fd);
+	closedir(dir);
+
+	return error;
+}
+
+
+static int fdinfo_init(void *p)
+{
+  ST_SCHEMA_TABLE *schema= (ST_SCHEMA_TABLE *) p;
+
+  schema->fields_info= fdinfo_fields;
+  schema->fill_table= fdinfo_fill;
+
+  return 0;
+}
+
+
+
 
 maria_declare_plugin(proc_info)
 {
@@ -65,7 +149,7 @@ maria_declare_plugin(proc_info)
   "PROC_MEMINFO",                  /* name                */
   ""      ,                        /* author              */
   "Useful information from /proc", /* description         */
-  PLUGIN_LICENSE_BSD,              /* license             */
+  PLUGIN_LICENSE_GPL,              /* license             */
   meminfo_init,                    /* init callback       */
   0,                               /* deinit callback     */
   0x0100,                          /* version as hex      */
@@ -73,5 +157,21 @@ maria_declare_plugin(proc_info)
   NULL,                            /* system variables    */
   "1.0",                           /* version as a string */
   MariaDB_PLUGIN_MATURITY_EXPERIMENTAL
+},
+
+{
+  MYSQL_INFORMATION_SCHEMA_PLUGIN, /* type                */
+  &fdinfo_plugin,                  /* information schema  */
+  "PROC_FDINFO",                   /* name                */
+  ""      ,                        /* author              */
+  "Useful information from /proc", /* description         */
+  PLUGIN_LICENSE_GPL,              /* license             */
+  fdinfo_init,                     /* init callback       */
+  0,                               /* deinit callback     */
+  0x0100,                          /* version as hex      */
+  NULL,                            /* status variables    */
+  NULL,                            /* system variables    */
+  "1.0",                           /* version as a string */
+  MariaDB_PLUGIN_MATURITY_EXPERIMENTAL
 }
 maria_declare_plugin_end;