Use shared_mutex for fuse log config

- Guard fuse_cfg_t log file and filepath shared pointers with a shared mutex
- Replace atomic shared pointer loads and stores with shared and unique locks

vendored/libfuse/include/fuse_cfg.hpp

@@ -5,6 +5,7 @@
 #include <climits>
 #include <cstdio>
 #include <memory>
+#include <shared_mutex>
 #include <string>
 
 #define FUSE_CFG_INVALID_ID    -1
@@ -33,6 +34,7 @@ struct fuse_cfg_t
   std::shared_ptr<std::string> log_filepath() const;
   void log_filepath(const std::string &);
 private:
+  mutable std::shared_mutex    _log_mutex;
   std::shared_ptr<FILE>        _log_file     = sp<FILE>(stderr,[](FILE*){});
   std::shared_ptr<std::string> _log_filepath = sp<std::string>();
 

vendored/libfuse/lib/fuse_cfg.cpp

@@ -1,5 +1,7 @@
 #include "fuse_cfg.hpp"
 
+#include <mutex>
+
 fuse_cfg_t fuse_cfg;
 
 bool
@@ -23,24 +25,32 @@ fuse_cfg_t::valid_umask() const
 std::shared_ptr<FILE>
 fuse_cfg_t::log_file() const
 {
-  return std::atomic_load(&_log_file);
+  std::shared_lock<std::shared_mutex> lk(_log_mutex);
+
+  return _log_file;
 }
 
 void
 fuse_cfg_t::log_file(std::shared_ptr<FILE> f_)
 {
-  std::atomic_store(&_log_file, f_);
+  std::unique_lock<std::shared_mutex> lk(_log_mutex);
+
+  _log_file = std::move(f_);
 }
 
 std::shared_ptr<std::string>
 fuse_cfg_t::log_filepath() const
 {
-  return std::atomic_load(&_log_filepath);
+  std::shared_lock<std::shared_mutex> lk(_log_mutex);
+
+  return _log_filepath;
 }
 
 void
 fuse_cfg_t::log_filepath(const std::string &s_)
 {
-  std::atomic_store(&_log_filepath,
-                    std::make_shared<std::string>(s_));
+  auto filepath = std::make_shared<std::string>(s_);
+  std::unique_lock<std::shared_mutex> lk(_log_mutex);
+
+  _log_filepath = std::move(filepath);
 }