daemon: check whether log file is regular and may be flushed (#4612)

daemon/daemon.cc

@@ -172,6 +172,7 @@ bool tr_daemon::reopen_log_file(char const* filename)
     }
 
     logfile_ = new_log_file;
+    logfile_flush_ = tr_sys_file_flush_possible(logfile_);
 
     if (old_log_file != TR_BAD_SYS_FILE)
     {
@@ -362,7 +363,7 @@ static void printMessage(
 #endif
 }
 
-static void pumpLogMessages(tr_sys_file_t file)
+static void pumpLogMessages(tr_sys_file_t file, bool flush)
 {
     tr_log_message* list = tr_logGetQueue();
 
@@ -371,7 +372,7 @@ static void pumpLogMessages(tr_sys_file_t file)
         printMessage(file, l->level, l->name, l->message, l->file, l->line);
     }
 
-    if (file != TR_BAD_SYS_FILE)
+    if (flush && file != TR_BAD_SYS_FILE)
     {
         tr_sys_file_flush(file);
     }
@@ -396,7 +397,7 @@ void tr_daemon::report_status(void)
 
 void tr_daemon::periodic_update(void)
 {
-    pumpLogMessages(logfile_);
+    pumpLogMessages(logfile_, logfile_flush_);
     report_status();
 }
 
@@ -852,7 +853,7 @@ CLEANUP:
 
     tr_sessionSaveSettings(my_session_, cdir, &settings_);
     tr_sessionClose(my_session_);
-    pumpLogMessages(logfile_);
+    pumpLogMessages(logfile_, logfile_flush_);
     printf(" done.\n");
 
     /* shutdown */
@@ -899,6 +900,7 @@ bool tr_daemon::init(int argc, char const* const argv[], bool* foreground, int*
     if (*foreground && logfile_ == TR_BAD_SYS_FILE)
     {
         logfile_ = tr_sys_file_get_std(TR_STD_SYS_FILE_ERR);
+        logfile_flush_ = tr_sys_file_flush_possible(logfile_);
     }
 
     if (!loaded)

daemon/daemon.h

@@ -47,6 +47,7 @@ private:
     bool seen_hup_ = false;
     std::string config_dir_;
     tr_variant settings_ = {};
+    bool logfile_flush_ = false;
     tr_session* my_session_ = nullptr;
     char const* log_file_name_ = nullptr;
     struct event_base* ev_base_ = nullptr;

libtransmission/file-posix.cc

@@ -798,7 +798,7 @@ bool tr_sys_file_flush(tr_sys_file_t handle, tr_error** error)
 {
     TR_ASSERT(handle != TR_BAD_SYS_FILE);
 
-    bool const ret = (isatty(handle) != 0) || (fsync(handle) != -1);
+    bool const ret = (fsync(handle) != -1);
 
     if (!ret)
     {
@@ -808,6 +808,21 @@ bool tr_sys_file_flush(tr_sys_file_t handle, tr_error** error)
     return ret;
 }
 
+bool tr_sys_file_flush_possible(tr_sys_file_t handle, tr_error** error)
+{
+    TR_ASSERT(handle != TR_BAD_SYS_FILE);
+
+    struct stat statbuf;
+
+    if (fstat(handle, &statbuf) != 0)
+    {
+        set_system_error(error, errno);
+        return false;
+    }
+
+    return S_ISREG(statbuf.st_mode);
+}
+
 bool tr_sys_file_truncate(tr_sys_file_t handle, uint64_t size, tr_error** error)
 {
     TR_ASSERT(handle != TR_BAD_SYS_FILE);

libtransmission/file-win32.cc

@@ -1106,6 +1106,21 @@ bool tr_sys_file_flush(tr_sys_file_t handle, tr_error** error)
     return ret;
 }
 
+bool tr_sys_file_flush_possible(tr_sys_file_t handle, tr_error** error)
+{
+    TR_ASSERT(handle != TR_BAD_SYS_FILE);
+
+    DWORD type = GetFileType(handle);
+
+    if (type == FILE_TYPE_UNKNOWN)
+    {
+        set_system_error(error, GetLastError());
+        return false;
+    }
+
+    return type == FILE_TYPE_DISK;
+}
+
 bool tr_sys_file_truncate(tr_sys_file_t handle, uint64_t size, tr_error** error)
 {
     TR_ASSERT(handle != TR_BAD_SYS_FILE);

libtransmission/file.h

@@ -445,6 +445,9 @@ bool tr_sys_file_write_at(
  */
 bool tr_sys_file_flush(tr_sys_file_t handle, struct tr_error** error = nullptr);
 
+/* @brief Check whether `handle` may be flushed via `tr_sys_file_flush()`. */
+bool tr_sys_file_flush_possible(tr_sys_file_t handle, struct tr_error** error = nullptr);
+
 /**
  * @brief Portability wrapper for `ftruncate()`.
  *