os/bluestore: let split() return string_view

instead of creating two strings, just return string_views, for better
performance. and for better readability.

Signed-off-by: Kefu Chai <kchai@redhat.com>
(cherry picked from commit afc2c61a3ac6904f3c5ca0cede053cb4920baf90)

diff --git a/src/os/bluestore/BlueRocksEnv.cc b/src/os/bluestore/BlueRocksEnv.cc
index b3dd73a74428289f30c469328adbca1609413e22..8c4f80c7ed10bfb46d761cb3778b6cfedd1e8f93 100644 (file)
--- a/src/os/bluestore/BlueRocksEnv.cc
+++ b/src/os/bluestore/BlueRocksEnv.cc
@@ -30,13 +30,17 @@ rocksdb::Status err_to_status(int r)
   }
 }
 
-void split(const std::string &fn, std::string *dir, std::string *file)
+std::pair<std::string_view, std::string_view>
+split(const std::string &fn)
 {
   size_t slash = fn.rfind('/');
-  *file = fn.substr(slash + 1);
-  while (slash && fn[slash-1] == '/')
+  assert(slash != fn.npos);
+  size_t file_begin = slash + 1;
+  while (slash && fn[slash - 1] == '/')
     --slash;
-  *dir = fn.substr(0, slash);
+  return {string_view(fn.data(), slash),
+          string_view(fn.data() + file_begin,
+                     fn.size() - file_begin)};
 }
 
 }
@@ -353,8 +357,7 @@ rocksdb::Status BlueRocksEnv::NewSequentialFile(
 {
   if (fname[0] == '/')
     return target()->NewSequentialFile(fname, result, options);
-  std::string dir, file;
-  split(fname, &dir, &file);
+  auto [dir, file] = split(fname);
   BlueFS::FileReader *h;
   int r = fs->open_for_read(dir, file, &h, false);
   if (r < 0)
@@ -368,8 +371,7 @@ rocksdb::Status BlueRocksEnv::NewRandomAccessFile(
   std::unique_ptr<rocksdb::RandomAccessFile>* result,
   const rocksdb::EnvOptions& options)
 {
-  std::string dir, file;
-  split(fname, &dir, &file);
+  auto [dir, file] = split(fname);
   BlueFS::FileReader *h;
   int r = fs->open_for_read(dir, file, &h, true);
   if (r < 0)
@@ -383,8 +385,7 @@ rocksdb::Status BlueRocksEnv::NewWritableFile(
   std::unique_ptr<rocksdb::WritableFile>* result,
   const rocksdb::EnvOptions& options)
 {
-  std::string dir, file;
-  split(fname, &dir, &file);
+  auto [dir, file] = split(fname);
   BlueFS::FileWriter *h;
   int r = fs->open_for_write(dir, file, &h, false);
   if (r < 0)
@@ -399,10 +400,8 @@ rocksdb::Status BlueRocksEnv::ReuseWritableFile(
   std::unique_ptr<rocksdb::WritableFile>* result,
   const rocksdb::EnvOptions& options)
 {
-  std::string old_dir, old_file;
-  split(old_fname, &old_dir, &old_file);
-  std::string new_dir, new_file;
-  split(new_fname, &new_dir, &new_file);
+  auto [old_dir, old_file] = split(old_fname);
+  auto [new_dir, new_file] = split(new_fname);
 
   int r = fs->rename(old_dir, old_file, new_dir, new_file);
   if (r < 0)
@@ -430,8 +429,7 @@ rocksdb::Status BlueRocksEnv::FileExists(const std::string& fname)
 {
   if (fname[0] == '/')
     return target()->FileExists(fname);
-  std::string dir, file;
-  split(fname, &dir, &file);
+  auto [dir, file] = split(fname);
   if (fs->stat(dir, file, NULL, NULL) == 0)
     return rocksdb::Status::OK();
   return err_to_status(-ENOENT);
@@ -450,8 +448,7 @@ rocksdb::Status BlueRocksEnv::GetChildren(
 
 rocksdb::Status BlueRocksEnv::DeleteFile(const std::string& fname)
 {
-  std::string dir, file;
-  split(fname, &dir, &file);
+  auto [dir, file] = split(fname);
   int r = fs->unlink(dir, file);
   if (r < 0)
     return err_to_status(r);
@@ -486,8 +483,7 @@ rocksdb::Status BlueRocksEnv::GetFileSize(
   const std::string& fname,
   uint64_t* file_size)
 {
-  std::string dir, file;
-  split(fname, &dir, &file);
+  auto [dir, file] = split(fname);
   int r = fs->stat(dir, file, file_size, NULL);
   if (r < 0)
     return err_to_status(r);
@@ -497,8 +493,7 @@ rocksdb::Status BlueRocksEnv::GetFileSize(
 rocksdb::Status BlueRocksEnv::GetFileModificationTime(const std::string& fname,
                                                      uint64_t* file_mtime)
 {
-  std::string dir, file;
-  split(fname, &dir, &file);
+  auto [dir, file] = split(fname);
   utime_t mtime;
   int r = fs->stat(dir, file, NULL, &mtime);
   if (r < 0)
@@ -511,10 +506,8 @@ rocksdb::Status BlueRocksEnv::RenameFile(
   const std::string& src,
   const std::string& target)
 {
-  std::string old_dir, old_file;
-  split(src, &old_dir, &old_file);
-  std::string new_dir, new_file;
-  split(target, &new_dir, &new_file);
+  auto [old_dir, old_file] = split(src);
+  auto [new_dir, new_file] = split(target);
 
   int r = fs->rename(old_dir, old_file, new_dir, new_file);
   if (r < 0)
@@ -537,8 +530,7 @@ rocksdb::Status BlueRocksEnv::AreFilesSame(
     if (fs->dir_exists(path)) {
       continue;
     }
-    std::string dir, file;
-    split(path, &dir, &file);
+    auto [dir, file] = split(path);
     int r = fs->stat(dir, file, nullptr, nullptr);
     if (!r) {
       continue;
@@ -556,8 +548,7 @@ rocksdb::Status BlueRocksEnv::LockFile(
   const std::string& fname,
   rocksdb::FileLock** lock)
 {
-  std::string dir, file;
-  split(fname, &dir, &file);
+  auto [dir, file] = split(fname);
   BlueFS::FileLock *l = NULL;
   int r = fs->lock_file(dir, file, &l);
   if (r < 0)