feat: Add example code for RocksDB - ZenFS application

.gitignore

@@ -3,3 +3,5 @@ fs/*.o
 fs/*.cc.d
 tests/results
 fs/version.h
+examples/*.o
+examples/*.cc.d

README.md

@@ -195,6 +195,6 @@ ZenFS uses clang-format with Google code style. You may run the following comman
 before submitting a PR.
 
 ```bash
-clang-format-11 -n -Werror --style=file fs/* util/zenfs.cc # Check for style issues
-clang-format-11 -i --style=file fs/* util/zenfs.cc         # Auto-fix the style issues
+clang-format-11 -n -Werror --style=file fs/* util/zenfs.cc examples/*.cc  # Check for style issues
+clang-format-11 -i --style=file fs/* util/zenfs.cc examples/*.cc          # Auto-fix the style issues
 ```

examples/README.md

@@ -0,0 +1,16 @@
+#Writing RocksDB applications with the ZenFS plugin
+
+The ZenFS plugin can also be used in your own RocksDB applications.
+To help you writing your own applications you can refer to the examples in this
+directory.
+
+To compile an example application you first need to build RocksDB with the
+ZenFS plugin acording to
+[this section](https://github.com/westerndigitalcorporation/zenfs#build).
+
+Then you can run:
+```
+g++ -I../../.. -I../../../include  $(pkg-config --cflags rocksdb) -c ./rw_key.cc -o ./rw_key.o
+g++ -L../../.. $(pkg-config --static --libs rocksdb) ./rw_key.o -o ./rw_key
+./rw_key nvmeXnX
+```

examples/rw_key.cc

@@ -0,0 +1,66 @@
+#include <assert.h>
+
+#include <iostream>
+
+#include "rocksdb/db.h"
+#include "rocksdb/env.h"
+#include "rocksdb/options.h"
+#include "rocksdb/utilities/options_util.h"
+
+int main(int argc, char* argv[]) {
+  if (argc != 2) {
+    printf("Usage:\n\t%s <device-name>\nE.g.:\n\t%s nvme0n1\n", argv[0],
+           argv[0]);
+    return 1;
+  }
+
+  int ret = 0;
+  std::string test_value;
+  std::string device_name = argv[1];
+  rocksdb::DB* db;
+  static std::shared_ptr<rocksdb::Env> fs_env_guard;
+  static rocksdb::Env* fs_env = nullptr;
+  rocksdb::Options options;
+  options.create_if_missing = true;
+  options.use_direct_io_for_flush_and_compaction = true;
+  rocksdb::ConfigOptions config_options(options);
+
+  rocksdb::Env::CreateFromUri(config_options, "", "zenfs://dev:" + device_name,
+                              &fs_env, &fs_env_guard);
+  options.env = fs_env;
+
+  // Open database
+  rocksdb::Status status = rocksdb::DB::Open(options, "rocksdbtest", &db);
+  if (!status.ok()) {
+    std::cerr << "Could not open the database: " << status.ToString()
+              << std::endl;
+    ret = 1;
+    goto out;
+  }
+
+  // Write
+  status =
+      db->Put(rocksdb::WriteOptions(), "zenfs_test_var", "zenfs_test_value");
+  if (!status.ok()) {
+    std::cerr << "Could not write test value to the database: "
+              << status.ToString() << std::endl;
+    ret = 1;
+  }
+
+  // Read
+  status = db->Get(rocksdb::ReadOptions(), "zenfs_test_var", &test_value);
+  if (!status.ok()) {
+    std::cerr << "Could not read test value to the database: "
+              << status.ToString() << std::endl;
+    ret = 1;
+    goto out;
+  } else {
+    std::cout << "Value was successfully written and read: " << test_value
+              << std::endl;
+    ret = 0;
+  }
+
+out:
+  if (db) delete db;
+  return ret;
+}