Patch-Source: https://github.com/ceph/ceph/commit/c0a3d46029757863e6c4b7c317ed31236b8c1345
From c0a3d46029757863e6c4b7c317ed31236b8c1345 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E8=83=A1=E7=8E=AE=E6=96=87?= <huww98@outlook.com>
Date: Wed, 22 Dec 2021 01:46:32 +0800
Subject: [PATCH] mon: use fmt::format for stderr cluster logging
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Just like 8e78ca5f958 but for mon cluster log.

Signed-off-by: 胡玮文 <huww98@outlook.com>
---
 src/mon/LogMonitor.cc | 26 ++++++++++++++------------
 src/mon/LogMonitor.h  |  2 +-
 2 files changed, 15 insertions(+), 13 deletions(-)

diff --git a/src/mon/LogMonitor.cc b/src/mon/LogMonitor.cc
index 094ea54b65247..e6d1029a1f7b3 100644
--- a/src/mon/LogMonitor.cc
+++ b/src/mon/LogMonitor.cc
@@ -42,6 +42,7 @@
 
 #include <boost/algorithm/string/predicate.hpp>
 
+#include <iterator>
 #include <sstream>
 #include <syslog.h>
 
@@ -354,10 +355,6 @@ void LogMonitor::log_external(const LogEntry& le)
     channel = CLOG_CHANNEL_CLUSTER;
   }
 
-  if (g_conf().get_val<bool>("mon_cluster_log_to_stderr")) {
-    cerr << channel << " " << le << std::endl;
-  }
-
   if (channels.do_log_to_syslog(channel)) {
     string level = channels.get_level(channel);
     string facility = channels.get_facility(channel);
@@ -386,21 +383,19 @@ void LogMonitor::log_external(const LogEntry& le)
     dout(7) << "journald: " << channel << dendl;
   }
 
+  bool do_stderr = g_conf().get_val<bool>("mon_cluster_log_to_stderr");
+  int fd = -1;
   if (g_conf()->mon_cluster_log_to_file) {
     if (this->log_rotated.exchange(false)) {
       this->log_external_close_fds();
     }
 
     auto p = channel_fds.find(channel);
-    int fd;
     if (p == channel_fds.end()) {
       string log_file = channels.get_log_file(channel);
       dout(20) << __func__ << " logging for channel '" << channel
 	       << "' to file '" << log_file << "'" << dendl;
-      if (log_file.empty()) {
-	// do not log this channel
-	fd = -1;
-      } else {
+      if (!log_file.empty()) {
 	fd = ::open(log_file.c_str(), O_WRONLY|O_APPEND|O_CREAT|O_CLOEXEC, 0600);
 	if (fd < 0) {
 	  int err = -errno;
@@ -413,11 +408,12 @@ void LogMonitor::log_external(const LogEntry& le)
     } else {
       fd = p->second;
     }
+  }
+  if (do_stderr || fd >= 0) {
+    fmt::format_to(std::back_inserter(log_buffer), "{}\n", le);
 
     if (fd >= 0) {
-      fmt::format_to(std::back_inserter(file_log_buffer), "{}\n", le);
-      int err = safe_write(fd, file_log_buffer.data(), file_log_buffer.size());
-      file_log_buffer.clear();
+      int err = safe_write(fd, log_buffer.data(), log_buffer.size());
       if (err < 0) {
 	dout(1) << "error writing to '" << channels.get_log_file(channel)
 		<< "' for channel '" << channel
@@ -426,6 +422,12 @@ void LogMonitor::log_external(const LogEntry& le)
 	channel_fds.erase(channel);
       }
     }
+
+    if (do_stderr) {
+      fmt::print(std::cerr, "{} {}", channel, std::string_view(log_buffer.data(), log_buffer.size()));
+    }
+
+    log_buffer.clear();
   }
 }
 
diff --git a/src/mon/LogMonitor.h b/src/mon/LogMonitor.h
index f6b433096e45a..1eccaa5c20379 100644
--- a/src/mon/LogMonitor.h
+++ b/src/mon/LogMonitor.h
@@ -51,7 +51,7 @@ class LogMonitor : public PaxosService,
   version_t external_log_to = 0;
   std::map<std::string, int> channel_fds;
 
-  fmt::memory_buffer file_log_buffer;
+  fmt::memory_buffer log_buffer;
   std::atomic<bool> log_rotated = false;
 
   struct log_channel_info {