Add option to wait for branches to become new mounts

branches-mount-timeout=UINT64 in seconds (default: 0)

LICENSE

@@ -1,7 +1,7 @@
 /*
   ISC License
 
-  Copyright (c) 2021, Antonio SJ Musumeci <trapexit@spawn.link>
+  Copyright (c) 2023, Antonio SJ Musumeci <trapexit@spawn.link>
 
   Permission to use, copy, modify, and/or distribute this software for any
   purpose with or without fee is hereby granted, provided that the above

README.md

@@ -1,6 +1,6 @@
 % mergerfs(1) mergerfs user manual
 % Antonio SJ Musumeci <trapexit@spawn.link>
-% 2023-01-16
+% 2023-01-24
 
 # NAME
 
@@ -165,6 +165,9 @@ These options are the same regardless of whether you use them with the `mergerfs
 * **nfsopenhack=off|git|all**: A workaround for exporting mergerfs
   over NFS where there are issues with creating files for write while
   setting the mode to read-only. (default: off)
+* **branches-mount-timeout=UINT**: Number of seconds to wait at
+  startup for branches to be a mount other than the mountpoint's
+  filesystem. (default: 0)
 * **follow-symlinks=never|directory|regular|all**: Turns symlinks into
   what they point to. (default: never)
 * **link-exdev=passthrough|rel-symlink|abs-base-symlink|abs-pool-symlink**:

src/branches.cpp

@@ -363,6 +363,17 @@ Branches::Impl::to_paths(StrVec &paths_) const
     }
 }
 
+fs::PathVector
+Branches::Impl::to_paths() const
+{
+  fs::PathVector vp;
+
+  for(const auto &branch : *this)
+    vp.emplace_back(branch.path);
+
+  return vp;
+}
+
 int
 Branches::from_string(const std::string &str_)
 {

src/branches.hpp

@@ -19,7 +19,7 @@
 #pragma once
 
 #include "branch.hpp"
-#include "nonstd/optional.hpp"
+#include "fs_pathvector.hpp"
 #include "strvec.hpp"
 #include "tofrom_string.hpp"
 
@@ -49,6 +49,7 @@ public:
   public:
     const uint64_t& minfreespace(void) const;
     void to_paths(StrVec &strvec) const;
+    fs::PathVector to_paths() const;
 
   public:
     Impl& operator=(Impl &impl_);

src/config.cpp

@@ -53,6 +53,7 @@ namespace l
   readonly(const std::string &s_)
   {
     IFERT("async_read");
+    IFERT("branches-mount-timeout");
     IFERT("cache.symlinks");
     IFERT("cache.writeback");
     IFERT("fsname");
@@ -73,6 +74,7 @@ Config::Config()
     auto_cache(false),
     minfreespace(MINFREESPACE_DEFAULT),
     branches(minfreespace),
+    branches_mount_timeout(0),
     cache_attr(1),
     cache_entry(1),
     cache_files(CacheFiles::ENUM::LIBFUSE),
@@ -116,6 +118,7 @@ Config::Config()
   _map["async_read"]             = &async_read;
   _map["auto_cache"]             = &auto_cache;
   _map["branches"]               = &branches;
+  _map["branches-mount-timeout"] = &branches_mount_timeout;
   _map["cache.attr"]             = &cache_attr;
   _map["cache.entry"]            = &cache_entry;
   _map["cache.files"]            = &cache_files;

src/config.hpp

@@ -103,6 +103,7 @@ public:
   ConfigBOOL     auto_cache;
   ConfigUINT64   minfreespace;
   Branches       branches;
+  ConfigUINT64   branches_mount_timeout;
   ConfigUINT64   cache_attr;
   ConfigUINT64   cache_entry;
   CacheFiles     cache_files;

src/fs_pathvector.hpp

@@ -0,0 +1,10 @@
+#pragma once
+
+#include "ghc/filesystem.hpp"
+
+#include <vector>
+
+namespace fs
+{
+  typedef std::vector<ghc::filesystem::path> PathVector;
+}

src/fs_wait_for_mount.cpp

@@ -0,0 +1,112 @@
+/*
+  ISC License
+
+  Copyright (c) 2023, Antonio SJ Musumeci <trapexit@spawn.link>
+
+  Permission to use, copy, modify, and/or distribute this software for any
+  purpose with or without fee is hereby granted, provided that the above
+  copyright notice and this permission notice appear in all copies.
+
+  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+
+#include "fs_wait_for_mount.hpp"
+
+#include <thread>
+
+constexpr std::chrono::milliseconds SLEEP_DURATION = std::chrono::milliseconds(333);
+
+
+bool
+fs::wait_for_mount(const struct stat               &src_st_,
+                   const ghc::filesystem::path     &tgtpath_,
+                   const std::chrono::milliseconds &timeout_)
+{
+  int rv;
+  std::chrono::duration<double> time_diff;
+  std::chrono::time_point<std::chrono::steady_clock> start_time;
+
+  start_time = std::chrono::steady_clock::now();
+  while(true)
+    {
+      struct stat tgt_st;
+
+      rv = fs::stat(tgtpath_,&tgt_st);
+      if(rv == 0)
+        {
+          if(tgt_st.st_dev != src_st_.st_dev)
+            return true;
+        }
+
+      time_diff = (std::chrono::steady_clock::now() - start_time);
+      if(time_diff > timeout_)
+        return false;
+
+      std::this_thread::sleep_for(SLEEP_DURATION);
+    }
+
+  return false;
+}
+
+static
+void
+_wait_for_mount(const struct stat               &src_st_,
+                const fs::PathVector            &tgtpaths_,
+                const std::chrono::milliseconds &timeout_,
+                fs::PathVector                  &failed_paths_)
+{
+  bool rv;
+  fs::PathVector::const_iterator i;
+  std::chrono::milliseconds timeout;
+  std::chrono::milliseconds diff;
+  std::chrono::time_point<std::chrono::steady_clock> now;
+  std::chrono::time_point<std::chrono::steady_clock> start_time;
+
+  timeout = timeout_;
+  now = start_time = std::chrono::steady_clock::now();
+  for(auto i = tgtpaths_.begin(); i != tgtpaths_.end(); ++i)
+    {
+      diff = std::chrono::duration_cast<std::chrono::milliseconds>(now - start_time);
+      timeout -= diff;
+
+      rv = fs::wait_for_mount(src_st_,*i,timeout);
+      if(rv == false)
+        failed_paths_.push_back(*i);
+
+      now = std::chrono::steady_clock::now();
+    }
+}
+
+void
+fs::wait_for_mount(const struct stat               &src_st_,
+                   const fs::PathVector            &tgtpaths_,
+                   const std::chrono::milliseconds &timeout_,
+                   fs::PathVector                  &failed_paths_)
+{
+  if(tgtpaths_.empty())
+    return;
+
+  _wait_for_mount(src_st_,tgtpaths_,timeout_,failed_paths_);
+}
+
+void
+fs::wait_for_mount(const ghc::filesystem::path     &srcpath_,
+                   const fs::PathVector            &tgtpaths_,
+                   const std::chrono::milliseconds &timeout_,
+                   fs::PathVector                  &failed_paths_)
+{
+  int rv;
+  struct stat src_st;
+
+  rv = fs::stat(srcpath_,&src_st);
+  if(rv == -1)
+    return;
+
+  fs::wait_for_mount(src_st,tgtpaths_,timeout_,failed_paths_);
+}

src/fs_wait_for_mount.hpp

@@ -0,0 +1,50 @@
+/*
+  ISC License
+
+  Copyright (c) 2023, Antonio SJ Musumeci <trapexit@spawn.link>
+
+  Permission to use, copy, modify, and/or distribute this software for any
+  purpose with or without fee is hereby granted, provided that the above
+  copyright notice and this permission notice appear in all copies.
+
+  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+
+#pragma once
+
+#include "ghc/filesystem.hpp"
+
+#include "fs_pathvector.hpp"
+#include "fs_stat.hpp"
+
+#include <chrono>
+#include <vector>
+
+
+namespace fs
+{
+  typedef std::vector<ghc::filesystem::path> PathVector;
+
+  bool
+  wait_for_mount(const struct stat               &st,
+                 const ghc::filesystem::path     &tgtpath,
+                 const std::chrono::milliseconds &timeout);
+
+  void
+  wait_for_mount(const struct stat               &st,
+                 const fs::PathVector            &tgtpaths,
+                 const std::chrono::milliseconds &timeout,
+                 fs::PathVector                  &failed_paths);
+
+  void
+  wait_for_mount(const ghc::filesystem::path     &srcpath,
+                 const fs::PathVector            &tgtpaths,
+                 const std::chrono::milliseconds &timeout,
+                 fs::PathVector                  &failed_paths);
+}

src/mergerfs.cpp

@@ -14,6 +14,9 @@
   OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */
 
+#include "fs_wait_for_mount.hpp"
+#include "syslog.hpp"
+
 #include "fs_path.hpp"
 #include "mergerfs.hpp"
 #include "option_parser.hpp"
@@ -147,6 +150,33 @@ namespace l
     resources::setpriority(prio);
   }
 
+  static
+  void
+  wait_for_mount(const Config::Read &cfg_)
+  {
+    fs::PathVector paths;
+    fs::PathVector failed;
+    std::chrono::milliseconds timeout;
+
+    paths = cfg_->branches->to_paths();
+
+    syslog_info("Waiting %u seconds for branches to mount",
+                (uint64_t)cfg_->branches_mount_timeout);
+
+    timeout = std::chrono::milliseconds(cfg_->branches_mount_timeout * 1000);
+    fs::wait_for_mount((std::string)cfg_->mount,
+                       paths,
+                       timeout,
+                       failed);
+    for(auto &path : failed)
+      syslog_warning("Branch %s was not mounted within timeout",
+                     path.c_str());
+    if(failed.size())
+      syslog_warning("Continuing to mount mergerfs despite %u branches not "
+                     "being different from the mountpoint filesystem",
+                     failed.size());
+  }
+
   int
   main(const int   argc_,
        char      **argv_)
@@ -156,6 +186,8 @@ namespace l
     fuse_args       args;
     fuse_operations ops;
 
+    syslog_open();
+
     memset(&ops,0,sizeof(fuse_operations));
 
     args.argc      = argc_;
@@ -169,6 +201,9 @@ namespace l
         return 1;
       }
 
+    if(cfg->branches_mount_timeout > 0)
+      l::wait_for_mount(cfg);
+
     l::setup_resources();
     l::get_fuse_operations(ops,cfg->nullrw);
 

src/nonstd/optional.hpp

@@ -44,20 +44,26 @@
 # define optional_CONFIG_SELECT_OPTIONAL  ( optional_HAVE_STD_OPTIONAL ? optional_OPTIONAL_STD : optional_OPTIONAL_NONSTD )
 #endif
 
+// Control presence of extensions:
+
+#ifndef optional_CONFIG_NO_EXTENSIONS
+#define optional_CONFIG_NO_EXTENSIONS  0
+#endif
+
 // Control presence of exception handling (try and auto discover):
 
 #ifndef optional_CONFIG_NO_EXCEPTIONS
 # if defined(_MSC_VER)
 # include <cstddef>     // for _HAS_EXCEPTIONS
 # endif
-# if defined(__cpp_exceptions) || defined(__EXCEPTIONS) || (_HAS_EXCEPTIONS)
+# if defined(__cpp_exceptions) || defined(__EXCEPTIONS) || (defined(_HAS_EXCEPTIONS) && (_HAS_EXCEPTIONS))
 #  define optional_CONFIG_NO_EXCEPTIONS  0
 # else
 #  define optional_CONFIG_NO_EXCEPTIONS  1
 # endif
 #endif
 
-// C++ language version detection (C++20 is speculative):
+// C++ language version detection (C++23 is speculative):
 // Note: VC14.0/1900 (VS2015) lacks too much from C++14.
 
 #ifndef   optional_CPLUSPLUS
@@ -73,7 +79,8 @@
 #define optional_CPP11_OR_GREATER_ ( optional_CPLUSPLUS >= 201103L )
 #define optional_CPP14_OR_GREATER  ( optional_CPLUSPLUS >= 201402L )
 #define optional_CPP17_OR_GREATER  ( optional_CPLUSPLUS >= 201703L )
-#define optional_CPP20_OR_GREATER  ( optional_CPLUSPLUS >= 202000L )
+#define optional_CPP20_OR_GREATER  ( optional_CPLUSPLUS >= 202002L )
+#define optional_CPP23_OR_GREATER  ( optional_CPLUSPLUS >= 202300L )
 
 // C++ language version (represent 98 as 3):
 
@@ -782,7 +789,7 @@ union storage_t
 
     void construct_value( value_type && v )
     {
-        ::new( value_ptr() ) value_type( std::move( v ) );
+        ::new( const_cast<void *>(static_cast<const volatile void *>(value_ptr())) ) value_type( std::move( v ) );
     }
 
     template< class... Args >
@@ -794,13 +801,13 @@ union storage_t
     template< class... Args >
     void emplace( Args&&... args )
     {
-        ::new( value_ptr() ) value_type( std::forward<Args>(args)... );
+        ::new( const_cast<void *>(static_cast<const volatile void *>(value_ptr())) ) value_type( std::forward<Args>(args)... );
     }
 
     template< class U, class... Args >
     void emplace( std::initializer_list<U> il, Args&&... args )
     {
-        ::new( value_ptr() ) value_type( il, std::forward<Args>(args)... );
+        ::new( const_cast<void *>(static_cast<const volatile void *>(value_ptr())) ) value_type( il, std::forward<Args>(args)... );
     }
 
 #endif
@@ -1485,7 +1492,40 @@ public:
         return has_value() ? contained.value() : static_cast<value_type>( v );
     }
 
-#endif // optional_CPP11_OR_GREATER
+#endif // optional_HAVE( REF_QUALIFIER )
+
+#if !optional_CONFIG_NO_EXTENSIONS
+#if  optional_HAVE( REF_QUALIFIER )
+
+    template< typename F >
+    optional_constexpr value_type value_or_eval( F f ) const &
+    {
+        return has_value() ? contained.value() : f();
+    }
+
+    template< typename F >
+    optional_constexpr14 value_type value_or_eval( F f ) &&
+    {
+        if ( has_value() )
+        {
+            return std::move( contained.value() );
+        }
+        else
+        {
+            return f();
+        }
+    }
+
+#else
+
+    template< typename F >
+    optional_constexpr value_type value_or_eval( F f ) const
+    {
+        return has_value() ? contained.value() : f();
+    }
+
+#endif //  optional_HAVE( REF_QUALIFIER )
+#endif // !optional_CONFIG_NO_EXTENSIONS
 
     // x.x.3.6, modifiers
 
@@ -1530,37 +1570,37 @@ private:
 // Relational operators
 
 template< typename T, typename U >
-inline optional_constexpr bool operator==( optional<T> const & x, optional<U> const & y )
+optional_nodiscard optional_constexpr bool operator==( optional<T> const & x, optional<U> const & y )
 {
     return bool(x) != bool(y) ? false : !bool( x ) ? true : *x == *y;
 }
 
 template< typename T, typename U >
-inline optional_constexpr bool operator!=( optional<T> const & x, optional<U> const & y )
+optional_nodiscard optional_constexpr bool operator!=( optional<T> const & x, optional<U> const & y )
 {
     return !(x == y);
 }
 
 template< typename T, typename U >
-inline optional_constexpr bool operator<( optional<T> const & x, optional<U> const & y )
+optional_nodiscard optional_constexpr bool operator<( optional<T> const & x, optional<U> const & y )
 {
     return (!y) ? false : (!x) ? true : *x < *y;
 }
 
 template< typename T, typename U >
-inline optional_constexpr bool operator>( optional<T> const & x, optional<U> const & y )
+optional_nodiscard optional_constexpr bool operator>( optional<T> const & x, optional<U> const & y )
 {
     return (y < x);
 }
 
 template< typename T, typename U >
-inline optional_constexpr bool operator<=( optional<T> const & x, optional<U> const & y )
+optional_nodiscard optional_constexpr bool operator<=( optional<T> const & x, optional<U> const & y )
 {
     return !(y < x);
 }
 
 template< typename T, typename U >
-inline optional_constexpr bool operator>=( optional<T> const & x, optional<U> const & y )
+optional_nodiscard optional_constexpr bool operator>=( optional<T> const & x, optional<U> const & y )
 {
     return !(x < y);
 }
@@ -1568,73 +1608,73 @@ inline optional_constexpr bool operator>=( optional<T> const & x, optional<U> co
 // Comparison with nullopt
 
 template< typename T >
-inline optional_constexpr bool operator==( optional<T> const & x, nullopt_t /*unused*/ ) optional_noexcept
+optional_nodiscard optional_constexpr bool operator==( optional<T> const & x, nullopt_t /*unused*/ ) optional_noexcept
 {
     return (!x);
 }
 
 template< typename T >
-inline optional_constexpr bool operator==( nullopt_t /*unused*/, optional<T> const & x ) optional_noexcept
+optional_nodiscard optional_constexpr bool operator==( nullopt_t /*unused*/, optional<T> const & x ) optional_noexcept
 {
     return (!x);
 }
 
 template< typename T >
-inline optional_constexpr bool operator!=( optional<T> const & x, nullopt_t /*unused*/ ) optional_noexcept
+optional_nodiscard optional_constexpr bool operator!=( optional<T> const & x, nullopt_t /*unused*/ ) optional_noexcept
 {
     return bool(x);
 }
 
 template< typename T >
-inline optional_constexpr bool operator!=( nullopt_t /*unused*/, optional<T> const & x ) optional_noexcept
+optional_nodiscard optional_constexpr bool operator!=( nullopt_t /*unused*/, optional<T> const & x ) optional_noexcept
 {
     return bool(x);
 }
 
 template< typename T >
-inline optional_constexpr bool operator<( optional<T> const & /*unused*/, nullopt_t /*unused*/ ) optional_noexcept
+optional_nodiscard optional_constexpr bool operator<( optional<T> const & /*unused*/, nullopt_t /*unused*/ ) optional_noexcept
 {
     return false;
 }
 
 template< typename T >
-inline optional_constexpr bool operator<( nullopt_t /*unused*/, optional<T> const & x ) optional_noexcept
+optional_nodiscard optional_constexpr bool operator<( nullopt_t /*unused*/, optional<T> const & x ) optional_noexcept
 {
     return bool(x);
 }
 
 template< typename T >
-inline optional_constexpr bool operator<=( optional<T> const & x, nullopt_t /*unused*/ ) optional_noexcept
+optional_nodiscard optional_constexpr bool operator<=( optional<T> const & x, nullopt_t /*unused*/ ) optional_noexcept
 {
     return (!x);
 }
 
 template< typename T >
-inline optional_constexpr bool operator<=( nullopt_t /*unused*/, optional<T> const & /*unused*/ ) optional_noexcept
+optional_nodiscard optional_constexpr bool operator<=( nullopt_t /*unused*/, optional<T> const & /*unused*/ ) optional_noexcept
 {
     return true;
 }
 
 template< typename T >
-inline optional_constexpr bool operator>( optional<T> const & x, nullopt_t /*unused*/ ) optional_noexcept
+optional_nodiscard optional_constexpr bool operator>( optional<T> const & x, nullopt_t /*unused*/ ) optional_noexcept
 {
     return bool(x);
 }
 
 template< typename T >
-inline optional_constexpr bool operator>( nullopt_t /*unused*/, optional<T> const & /*unused*/ ) optional_noexcept
+optional_nodiscard optional_constexpr bool operator>( nullopt_t /*unused*/, optional<T> const & /*unused*/ ) optional_noexcept
 {
     return false;
 }
 
 template< typename T >
-inline optional_constexpr bool operator>=( optional<T> const & /*unused*/, nullopt_t /*unused*/ ) optional_noexcept
+optional_nodiscard optional_constexpr bool operator>=( optional<T> const & /*unused*/, nullopt_t /*unused*/ ) optional_noexcept
 {
     return true;
 }
 
 template< typename T >
-inline optional_constexpr bool operator>=( nullopt_t /*unused*/, optional<T> const & x ) optional_noexcept
+optional_nodiscard optional_constexpr bool operator>=( nullopt_t /*unused*/, optional<T> const & x ) optional_noexcept
 {
     return (!x);
 }
@@ -1642,73 +1682,73 @@ inline optional_constexpr bool operator>=( nullopt_t /*unused*/, optional<T> con
 // Comparison with T
 
 template< typename T, typename U >
-inline optional_constexpr bool operator==( optional<T> const & x, U const & v )
+optional_nodiscard optional_constexpr bool operator==( optional<T> const & x, U const & v )
 {
     return bool(x) ? *x == v : false;
 }
 
 template< typename T, typename U >
-inline optional_constexpr bool operator==( U const & v, optional<T> const & x )
+optional_nodiscard optional_constexpr bool operator==( U const & v, optional<T> const & x )
 {
     return bool(x) ? v == *x : false;
 }
 
 template< typename T, typename U >
-inline optional_constexpr bool operator!=( optional<T> const & x, U const & v )
+optional_nodiscard optional_constexpr bool operator!=( optional<T> const & x, U const & v )
 {
     return bool(x) ? *x != v : true;
 }
 
 template< typename T, typename U >
-inline optional_constexpr bool operator!=( U const & v, optional<T> const & x )
+optional_nodiscard optional_constexpr bool operator!=( U const & v, optional<T> const & x )
 {
     return bool(x) ? v != *x : true;
 }
 
 template< typename T, typename U >
-inline optional_constexpr bool operator<( optional<T> const & x, U const & v )
+optional_nodiscard optional_constexpr bool operator<( optional<T> const & x, U const & v )
 {
     return bool(x) ? *x < v : true;
 }
 
 template< typename T, typename U >
-inline optional_constexpr bool operator<( U const & v, optional<T> const & x )
+optional_nodiscard optional_constexpr bool operator<( U const & v, optional<T> const & x )
 {
     return bool(x) ? v < *x : false;
 }
 
 template< typename T, typename U >
-inline optional_constexpr bool operator<=( optional<T> const & x, U const & v )
+optional_nodiscard optional_constexpr bool operator<=( optional<T> const & x, U const & v )
 {
     return bool(x) ? *x <= v : true;
 }
 
 template< typename T, typename U >
-inline optional_constexpr bool operator<=( U const & v, optional<T> const & x )
+optional_nodiscard optional_constexpr bool operator<=( U const & v, optional<T> const & x )
 {
     return bool(x) ? v <= *x : false;
 }
 
 template< typename T, typename U >
-inline optional_constexpr bool operator>( optional<T> const & x, U const & v )
+optional_nodiscard optional_constexpr bool operator>( optional<T> const & x, U const & v )
 {
     return bool(x) ? *x > v : false;
 }
 
 template< typename T, typename U >
-inline optional_constexpr bool operator>( U const & v, optional<T> const & x )
+optional_nodiscard optional_constexpr bool operator>( U const & v, optional<T> const & x )
 {
     return bool(x) ? v > *x : true;
 }
 
 template< typename T, typename U >
-inline optional_constexpr bool operator>=( optional<T> const & x, U const & v )
+optional_nodiscard optional_constexpr bool operator>=( optional<T> const & x, U const & v )
 {
     return bool(x) ? *x >= v : false;
 }
 
 template< typename T, typename U >
-inline optional_constexpr bool operator>=( U const & v, optional<T> const & x )
+optional_nodiscard optional_constexpr bool operator>=( U const & v, optional<T> const & x )
 {
     return bool(x) ? v >= *x : true;
 }

src/syslog.cpp

@@ -0,0 +1,96 @@
+/*
+  ISC License
+
+  Copyright (c) 2023, Antonio SJ Musumeci <trapexit@spawn.link>
+
+  Permission to use, copy, modify, and/or distribute this software for any
+  purpose with or without fee is hereby granted, provided that the above
+  copyright notice and this permission notice appear in all copies.
+
+  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+
+#include <stdarg.h>
+#include <syslog.h>
+
+static bool g_SYSLOG_ENABLED = false;
+
+void
+syslog_open()
+{
+  const char *ident = "mergerfs";
+  const int   option = (LOG_CONS|LOG_PID);
+  const int   facility = LOG_USER;
+
+  openlog(ident,option,facility);
+  g_SYSLOG_ENABLED = true;
+}
+
+void
+syslog_close()
+{
+  closelog();
+  g_SYSLOG_ENABLED = false;
+}
+
+void
+syslog_log(const int   priority_,
+           const char *format_,
+           va_list     valist_)
+{
+  if(g_SYSLOG_ENABLED == false)
+    return;
+
+  vsyslog(priority_,format_,valist_);
+}
+
+void
+syslog_log(const int   priority_,
+           const char *format_,
+           ...)
+{
+  va_list valist;
+
+  va_start(valist,format_);
+  syslog_log(priority_,format_,valist);
+  va_end(valist);
+}
+
+void
+syslog_info(const char *format_,
+            ...)
+{
+  va_list valist;
+
+  va_start(valist,format_);
+  syslog_log(LOG_INFO,format_,valist);
+  va_end(valist);  
+}
+
+void
+syslog_warning(const char *format_,
+               ...)
+{
+  va_list valist;
+
+  va_start(valist,format_);
+  syslog_log(LOG_WARNING,format_,valist);
+  va_end(valist);  
+}
+
+void
+syslog_error(const char *format_,
+             ...)
+{
+  va_list valist;
+
+  va_start(valist,format_);
+  syslog_log(LOG_ERR,format_,valist);
+  va_end(valist);  
+}

src/syslog.hpp

@@ -0,0 +1,29 @@
+/*
+  ISC License
+
+  Copyright (c) 2023, Antonio SJ Musumeci <trapexit@spawn.link>
+
+  Permission to use, copy, modify, and/or distribute this software for any
+  purpose with or without fee is hereby granted, provided that the above
+  copyright notice and this permission notice appear in all copies.
+
+  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+
+#pragma once
+
+#include <syslog.h>
+
+
+void syslog_open();
+void syslog_log(const int priority, const char *format, ...);
+void syslog_info(const char *format, ...);
+void syslog_warning(const char *format, ...);
+void syslog_error(const char *format, ...);
+void syslog_close();