Support custom env in sst_dump (#5845)

Summary:
This PR allows for the creation of custom env when using sst_dump. If
the user does not set options.env or set options.env to nullptr, then sst_dump
will automatically try to create a custom env depending on the path to the sst
file or db directory. In order to use this feature, the user must call
ObjectRegistry::Register() beforehand.

Test Plan (on devserver):
```
$make all && make check
```
All tests must pass to ensure this change does not break anything.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5845

Differential Revision: D17678038

Pulled By: riversand963

fbshipit-source-id: 58ecb4b3f75246d52b07c4c924a63ee61c1ee626

2 files changed, 9 insertions, 0 deletions

diff --git a/include/rocksdb/env.h b/include/rocksdb/env.h
index b3b30b5ac..0c5e590b2 100644
--- a/include/rocksdb/env.h
+++ b/include/rocksdb/env.h
@@ -152,6 +152,10 @@ class Env {
   // Loads the environment specified by the input value into the result
   static Status LoadEnv(const std::string& value, Env** result);
 
+  // Loads the environment specified by the input value into the result
+  static Status LoadEnv(const std::string& value, Env** result,
+                        std::shared_ptr<Env>* guard);
+
   // Return a default environment suitable for the current operating
   // system.  Sophisticated users may wish to provide their own Env
   // implementation instead of relying on this default environment.
diff --git a/include/rocksdb/utilities/ldb_cmd.h b/include/rocksdb/utilities/ldb_cmd.h
index 3a5c980f4..cf7d25fba 100644
--- a/include/rocksdb/utilities/ldb_cmd.h
+++ b/include/rocksdb/utilities/ldb_cmd.h
@@ -29,6 +29,7 @@ namespace rocksdb {
 class LDBCommand {
  public:
   // Command-line arguments
+  static const std::string ARG_ENV_URI;
   static const std::string ARG_DB;
   static const std::string ARG_PATH;
   static const std::string ARG_SECONDARY_PATH;
@@ -128,6 +129,7 @@ class LDBCommand {
 
  protected:
   LDBCommandExecuteResult exec_state_;
+  std::string env_uri_;
   std::string db_path_;
   // If empty, open DB as primary. If non-empty, open the DB as secondary
   // with this secondary path. When running against a database opened by
@@ -176,6 +178,9 @@ class LDBCommand {
   /** List of command-line options valid for this command */
   const std::vector<std::string> valid_cmd_line_options_;
 
+  /** Shared pointer to underlying environment if applicable **/
+  std::shared_ptr<Env> env_guard_;
+
   bool ParseKeyValue(const std::string& line, std::string* key,
                      std::string* value, bool is_key_hex, bool is_value_hex);