MDEV-14533 Provide information_schema tables using which hardware

information can be obtained.

        DISKS plugin implementation added to the tree.

mysql-test/suite/plugins/r/disks.result

+install plugin DISKS soname 'disks';
+show create table information_schema.disks;
+Table	Create Table
+DISKS	CREATE TEMPORARY TABLE `DISKS` (
+  `Disk` varchar(4096) NOT NULL DEFAULT '',
+  `Path` varchar(4096) NOT NULL DEFAULT '',
+  `Total` int(32) NOT NULL DEFAULT '0',
+  `Used` int(32) NOT NULL DEFAULT '0',
+  `Available` int(32) NOT NULL DEFAULT '0'
+) ENGINE=MEMORY DEFAULT CHARSET=utf8
+select sum(Total) > sum(Available), sum(Total)>sum(Used) from information_schema.disks;
+sum(Total) > sum(Available)	sum(Total)>sum(Used)
+1	1
+uninstall plugin DISKS;

mysql-test/suite/plugins/t/disks.test

+--source include/not_windows.inc
+
+if (!$DISKS_SO) {
+  skip No DISKS plugin;
+}
+
+install plugin DISKS soname 'disks';
+show create table information_schema.disks;
+select sum(Total) > sum(Available), sum(Total)>sum(Used) from information_schema.disks;
+
+uninstall plugin DISKS;

plugin/information_schema_disks/CMakeLists.txt

+IF(NOT WIN32)
+  INCLUDE_DIRECTORIES(${CMAKE_SOURCE_DIR}/sql)
+  MYSQL_ADD_PLUGIN(DISKS information_schema_disks.cc MODULE_ONLY RECOMPILE_FOR_EMBEDDED)
+ENDIF()
+

plugin/information_schema_disks/README.txt

+Information Schema Disks
+------------------------
+This is a proof-of-concept information schema plugin that allows the
+disk space situation to be monitored. When installed, it can be used
+as follows:
+
+  > select * from information_schema.disks;
+  +-----------+-----------------------+-----------+----------+-----------+
+  | Disk      | Path                  | Total     | Used     | Available |
+  +-----------+-----------------------+-----------+----------+-----------+
+  | /dev/sda3 | /                     |  47929956 | 30666304 |  14805864 |
+  | /dev/sda1 | /boot/efi             |    191551 |     3461 |    188090 |
+  | /dev/sda4 | /home                 | 174679768 | 80335392 |  85448120 |
+  | /dev/sdb1 | /mnt/hdd              | 961301832 |    83764 | 912363644 |
+  | /dev/sdb1 | /home/wikman/Music    | 961301832 |    83764 | 912363644 |
+  | /dev/sdb1 | /home/wikman/Videos   | 961301832 |    83764 | 912363644 |
+  | /dev/sdb1 | /home/wikman/hdd      | 961301832 |    83764 | 912363644 |
+  | /dev/sdb1 | /home/wikman/Pictures | 961301832 |    83764 | 912363644 |
+  | /dev/sda3 | /var/lib/docker/aufs  |  47929956 | 30666304 |  14805864 |
+  +-----------+-----------------------+-----------+----------+-----------+
+  9 rows in set (0.00 sec)
+
+- 'Disk' is the name of the disk itself.
+- 'Path' is the mount point of the disk.
+- 'Total' is the total space in KiB.
+- 'Used' is the used amount of space in KiB, and
+- 'Available' is the amount of space in KiB available to non-root users.
+
+Note that as the amount of space available to root may be more that what
+is available to non-root users, 'available' + 'used' may be less than 'total'.
+
+All paths to which a particular disk has been mounted are reported. The
+rationale is that someone might want to take different action e.g. depending
+on which disk is relevant for a particular path. This leads to the same disk
+being reported multiple times. An alternative to this would be to have two
+tables; disks and mounts.
+
+  > select * from information_schema.disks;
+  +-----------+-----------+----------+-----------+
+  | Disk      | Total     | Used     | Available |
+  +-----------+-----------+----------+-----------+
+  | /dev/sda3 |  47929956 | 30666304 |  14805864 |
+  | /dev/sda1 |    191551 |     3461 |    188090 |
+  | /dev/sda4 | 174679768 | 80335392 |  85448120 |
+  | /dev/sdb1 | 961301832 |    83764 | 912363644 |
+  +-----------+-----------+----------+-----------+
+
+  > select * from information_schema.mounts;
+  +-----------------------+-----------+
+  | Path                  | Disk      |
+  +-----------------------+-----------+
+  | /                     | /dev/sda3 |
+  | /boot/efi             | /dev/sda1 |
+  | /home                 | /dev/sda4 |
+  | /mnt/hdd              | /dev/sdb1 |
+  | /home/wikman/Music    | /dev/sdb1 |
+  ...
+
+
+Building
+--------
+- Ensure that the directory information_schema_disks is in the top-level
+  directory of the server.
+- Add
+
+  ADD_SUBDIRECTORY(information_schema_disks)
+
+  to the top-level CMakeLists.txt
+
+> Invoke make
+
+  $ make
+
+Installation
+------------
+- Copy information_schema_disks/libinformation_schema_disks.so to the plugin
+  directory of the server:
+
+  $ cd information_schema_disks
+  $ sudo cp libinformation_schema_disks.so plugin-directory-of-server
+
+- Using mysql, install the plugin:
+
+  MariaDB [(none)]> install plugin disks soname 'libinformation_schema_disks.so';
+
+Usage
+-----
+The plugin appears as the table 'disks' in 'information_schema'.
+
+  MariaDB [(none)]> select * from information_schema.disks;
+  +-----------+-----------------------+-----------+----------+-----------+
+  | Disk      | Path                  | Total     | Used     | Available |
+  +-----------+-----------------------+-----------+----------+-----------+
+  | /dev/sda3 | /                     |  47929956 | 30666308 |  14805860 |
+  | /dev/sda1 | /boot/efi             |    191551 |     3461 |    188090 |
+  | /dev/sda4 | /home                 | 174679768 | 80348148 |  85435364 |
+  | /dev/sdb1 | /mnt/hdd              | 961301832 |    83764 | 912363644 |
+  | /dev/sdb1 | /home/wikman/Music    | 961301832 |    83764 | 912363644 |
+  | /dev/sdb1 | /home/wikman/Videos   | 961301832 |    83764 | 912363644 |
+  ...
+

plugin/information_schema_disks/information_schema_disks.cc

+/*
+   Copyright (c) 2017, MariaDB
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; version 2 of the License.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA */
+
+#include <sys/statvfs.h>
+#include <sys/types.h>
+#include <mntent.h>
+#include <sql_class.h>
+#include <table.h>
+#include <innodb_priv.h>
+
+namespace
+{
+
+struct st_mysql_information_schema disks_table_info = { MYSQL_INFORMATION_SCHEMA_INTERFACE_VERSION };
+
+ST_FIELD_INFO disks_table_fields[]=
+{
+    { "Disk",      PATH_MAX, MYSQL_TYPE_STRING, 0, 0 ,0, 0 },
+    { "Path",      PATH_MAX, MYSQL_TYPE_STRING, 0, 0 ,0, 0 },
+    { "Total",           32, MYSQL_TYPE_LONG,   0, 0 ,0 ,0 }, // Total amount available
+    { "Used",            32, MYSQL_TYPE_LONG,   0, 0 ,0 ,0 }, // Amount of space used
+    { "Available",       32, MYSQL_TYPE_LONG,   0, 0 ,0 ,0 }, // Amount available to users other than root.
+    { 0, 0, MYSQL_TYPE_NULL, 0, 0, 0, 0 }
+};
+
+int disks_table_add_row(THD* pThd,
+                        TABLE* pTable,
+                        const char* zDisk,
+                        const char* zPath,
+                        const struct statvfs& info)
+{
+    // From: http://pubs.opengroup.org/onlinepubs/009695399/basedefs/sys/statvfs.h.html
+    //
+    // f_frsize   Fundamental file system block size.
+    // f_blocks   Total number of blocks on file system in units of f_frsize.
+    // f_bfree    Total number of free blocks.
+    // f_bavail   Number of free blocks available to non-privileged process.
+
+    size_t total = (info.f_frsize * info.f_blocks) / 1024;
+    size_t used  = (info.f_frsize * (info.f_blocks - info.f_bfree)) / 1024;
+    size_t avail = (info.f_frsize * info.f_bavail) / 1024;
+
+    pTable->field[0]->store(zDisk, strlen(zDisk), system_charset_info);
+    pTable->field[1]->store(zPath, strlen(zPath), system_charset_info);
+    pTable->field[2]->store(total);
+    pTable->field[3]->store(used);
+    pTable->field[4]->store(avail);
+
+    // 0 means success.
+    return (schema_table_store_record(pThd, pTable) != 0) ? 1 : 0;
+}
+
+int disks_table_add_row(THD* pThd, TABLE* pTable, const char* zDisk, const char* zPath)
+{
+    int rv = 0;
+
+    struct statvfs info;
+
+    if (statvfs(zPath, &info) == 0) // We ignore failures.
+    {
+        rv = disks_table_add_row(pThd, pTable, zDisk, zPath, info);
+    }
+
+    return rv;
+}
+
+int disks_fill_table(THD* pThd, TABLE_LIST* pTables, Item* pCond)
+{
+    int rv = 1;
+    TABLE* pTable = pTables->table;
+
+    FILE* pFile = setmntent("/etc/mtab", "r");
+
+    if (pFile)
+    {
+        const size_t BUFFER_SIZE = 4096; // 4K should be sufficient.
+
+        char* pBuffer = new (std::nothrow) char [BUFFER_SIZE];
+
+        if (pBuffer)
+        {
+            rv = 0;
+
+            struct mntent ent;
+            struct mntent* pEnt;
+
+            while ((rv == 0) && (pEnt = getmntent_r(pFile, &ent, pBuffer, BUFFER_SIZE)))
+            {
+                // We only report the ones that refer to physical disks.
+                if (pEnt->mnt_fsname[0] == '/')
+                {
+                    rv = disks_table_add_row(pThd, pTable, pEnt->mnt_fsname, pEnt->mnt_dir);
+                }
+            }
+
+            delete [] pBuffer;
+        }
+        else
+        {
+            rv = 1;
+        }
+
+        endmntent(pFile);
+    }
+
+    return rv;
+}
+
+int disks_table_init(void *ptr)
+{
+    ST_SCHEMA_TABLE* pSchema_table = (ST_SCHEMA_TABLE*)ptr;
+
+    pSchema_table->fields_info = disks_table_fields;
+    pSchema_table->fill_table = disks_fill_table;
+    return 0;
+}
+
+}
+
+extern "C"
+{
+
+mysql_declare_plugin(disks_library)
+{
+    MYSQL_INFORMATION_SCHEMA_PLUGIN,
+    &disks_table_info,                 /* type-specific descriptor */
+    "DISKS",                           /* table name */
+    "MariaDB",                         /* author */
+    "Disk space information",          /* description */
+    PLUGIN_LICENSE_GPL,                /* license type */
+    disks_table_init,                  /* init function */
+    NULL,
+    0x0100,                            /* version = 1.0 */
+    NULL,                              /* no status variables */
+    NULL,                              /* no system variables */
+    NULL,                              /* no reserved information */
+    0                                  /* no flags */
+}
+mysql_declare_plugin_end;
+
+}