Abort rocksdb startup if O_DIRECT is requested but not supported

Summary:
This change adds a check to see whether the filesystem backing
rocksdb_datadir allows O_DIRECT when use_direct_reads is true
and prevents rocksdb from coming up.

This fixes facebook#778
Closes facebook#793
GitHub Author: Roberto Rodriguez Alcala <rralcala@fb.com>

Test Plan: Imported from GitHub, without a `Test Plan:` line.

Reviewers: svcscm, generatedunixname499836121, herman, cday

Reviewed By: svcscm

Subscribers: phabricatorlinter, webscalesql-eng@fb.com

Differential Revision: https://phabricator.intern.facebook.com/D6995213

Tasks: T25106985

Signature: 6995213:1519151636:f3f9b9d4042ede899d84cc2104ca94cb2648ab7f

mysql-test/suite/rocksdb/r/use_direct_reads.result

@@ -0,0 +1,18 @@
+Checking direct reads
+CREATE TABLE t1 (pk INT PRIMARY KEY DEFAULT '0', a INT(11), b CHAR(8)) ENGINE=rocksdb;
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `pk` int(11) NOT NULL DEFAULT '0',
+  `a` int(11) DEFAULT NULL,
+  `b` char(8) DEFAULT NULL,
+  PRIMARY KEY (`pk`)
+) ENGINE=ROCKSDB DEFAULT CHARSET=latin1
+INSERT INTO t1 VALUES (1, 1,'a');
+INSERT INTO t1 (a,b) VALUES (2,'b');
+set global rocksdb_force_flush_memtable_now=1;
+SELECT a,b FROM t1;
+a	b
+1	a
+2	b
+DROP TABLE t1;

mysql-test/suite/rocksdb/t/use_direct_reads.test

@@ -0,0 +1,37 @@
+--source include/have_rocksdb.inc
+
+--perl
+use Cwd 'abs_path';
+
+open(FILE, ">", "$ENV{MYSQL_TMP_DIR}/data_in_shm.inc") or die;
+my $real_path= abs_path($ENV{'MYSQLTEST_VARDIR'});
+my $in_shm= index($real_path, "/dev/shm") != -1;
+print FILE "let \$DATA_IN_SHM= $in_shm;\n";
+close FILE;
+EOF
+
+--source $MYSQL_TMP_DIR/data_in_shm.inc
+--remove_file $MYSQL_TMP_DIR/data_in_shm.inc
+
+if ($DATA_IN_SHM)
+{
+  --skip DATADIR is in /dev/shm, possibly due to --mem
+}
+
+--echo Checking direct reads
+--let $_mysqld_option=--rocksdb_use_direct_reads=1
+--source include/restart_mysqld_with_option.inc
+
+CREATE TABLE t1 (pk INT PRIMARY KEY DEFAULT '0', a INT(11), b CHAR(8)) ENGINE=rocksdb;
+SHOW CREATE TABLE t1;
+INSERT INTO t1 VALUES (1, 1,'a');
+INSERT INTO t1 (a,b) VALUES (2,'b');
+set global rocksdb_force_flush_memtable_now=1;
+--sorted_result
+SELECT a,b FROM t1;
+DROP TABLE t1;
+
+# cleanup
+--let _$mysqld_option=
+--source include/restart_mysqld.inc
+

storage/rocksdb/ha_rocksdb.cc

@@ -4180,6 +4180,35 @@ static int rocksdb_init_func(void *const p) {
     DBUG_RETURN(HA_EXIT_FAILURE);
   }
 
+  // Check whether the filesystem backing rocksdb_datadir allows O_DIRECT
+  if (rocksdb_db_options->use_direct_reads) {
+    rocksdb::EnvOptions soptions;
+    rocksdb::Status check_status;
+    rocksdb::Env *const env = rocksdb_db_options->env;
+
+    std::string fname = format_string("%s/DIRECT_CHECK", rocksdb_datadir);
+    if (env->FileExists(fname).ok()) {
+      std::unique_ptr<rocksdb::SequentialFile> file;
+      soptions.use_direct_reads = true;
+      check_status = env->NewSequentialFile(fname, &file, soptions);
+    } else {
+      std::unique_ptr<rocksdb::WritableFile> file;
+      soptions.use_direct_writes = true;
+      check_status = env->ReopenWritableFile(fname, &file, soptions);
+      if (file != nullptr) {
+        file->Close();
+      }
+      env->DeleteFile(fname);
+    }
+
+    if (!check_status.ok()) {
+      sql_print_error("RocksDB: Unable to use direct io in rocksdb-datadir:"
+                              "(%s)", check_status.getState());
+      rdb_open_tables.free_hash();
+      DBUG_RETURN(HA_EXIT_FAILURE);
+    }
+  }
+
   if (rocksdb_db_options->allow_mmap_writes &&
       rocksdb_db_options->use_direct_io_for_flush_and_compaction) {
     // See above comment for allow_mmap_reads. (NO_LINT_DEBUG)