Fix ldb dump_manifest

Summary:
We now reads table properties in VersionSet::LogAndApply(), which requires options.db_paths to be set. But since ldb_cmd directly creates VersionSet without initialization db_paths, causing a seg fault. This patch fix it by initializing db_paths.

log_and_apply_bench still shows segfault, because table cache is nullptr in VersionSet created.

Test Plan: Run ldb dump_manifest which used to fail.

Reviewers: yhchiang, ljin, igor

Reviewed By: igor

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D20751

db/log_and_apply_bench.cc

@@ -42,6 +42,11 @@ void BM_LogAndApply(int iters, int num_base_files) {
 
     Options options;
     EnvOptions sopt;
+    // Notice we are using the default options not through SanitizeOptions().
+    // We might want to initialize some options manually if needed.
+    options.db_paths.emplace_back(dbname, 0);
+    // The parameter of table cache is passed in as null, so any file I/O
+    // operation is likely to fail.
     vset = new VersionSet(dbname, &options, sopt, nullptr);
     std::vector<ColumnFamilyDescriptor> dummy;
     dummy.push_back(ColumnFamilyDescriptor());

util/ldb_cmd.cc

@@ -556,6 +556,10 @@ void ManifestDumpCommand::DoCommand() {
   std::shared_ptr<Cache> tc(NewLRUCache(
       options.max_open_files - 10, options.table_cache_numshardbits,
       options.table_cache_remove_scan_count_limit));
+  // Notice we are using the default options not through SanitizeOptions(),
+  // if VersionSet::DumpManifest() depends on any option done by
+  // SanitizeOptions(), we need to initialize it manually.
+  options.db_paths.emplace_back("dummy", 0);
   VersionSet* versions = new VersionSet(dbname, &options, sopt, tc.get());
   Status s = versions->DumpManifest(options, file, verbose_, is_key_hex_);
   if (!s.ok()) {