Add `-debuglogfile` option

This patch adds an option to configure the name and/or directory of the
debug log.

The user can specify either a relative path, in which case the path
is relative to the data directory. They can also specify an absolute
path to put the log anywhere else in the file system.

src/init.cpp

@@ -342,6 +342,7 @@ std::string HelpMessage(HelpMessageMode mode)
     if (showDebug)
         strUsage += HelpMessageOpt("-feefilter", strprintf("Tell other nodes to filter invs to us by our mempool min fee (default: %u)", DEFAULT_FEEFILTER));
     strUsage += HelpMessageOpt("-loadblock=<file>", _("Imports blocks from external blk000??.dat file on startup"));
+    strUsage += HelpMessageOpt("-debuglogfile=<file>", strprintf(_("Specify location of debug log file: this can be an absolute path or a path relative to the data directory (default: %s)"), DEFAULT_DEBUGLOGFILE));
     strUsage += HelpMessageOpt("-maxorphantx=<n>", strprintf(_("Keep at most <n> unconnectable transactions in memory (default: %u)"), DEFAULT_MAX_ORPHAN_TRANSACTIONS));
     strUsage += HelpMessageOpt("-maxmempool=<n>", strprintf(_("Keep the transaction memory pool below <n> megabytes (default: %u)"), DEFAULT_MAX_MEMPOOL_SIZE));
     strUsage += HelpMessageOpt("-mempoolexpiry=<n>", strprintf(_("Do not keep transactions in the mempool longer than <n> hours (default: %u)"), DEFAULT_MEMPOOL_EXPIRY));
@@ -1209,8 +1210,11 @@ bool AppInitMain(boost::thread_group& threadGroup, CScheduler& scheduler)
         ShrinkDebugFile();
     }
 
-    if (fPrintToDebugLog)
-        OpenDebugLog();
+    if (fPrintToDebugLog) {
+        if (!OpenDebugLog()) {
+            return InitError(strprintf("Could not open debug log file %s", GetDebugLogPath().string()));
+        }
+    }
 
     if (!fLogTimestamps)
         LogPrintf("Startup time: %s\n", DateTimeStrFormat("%Y-%m-%d %H:%M:%S", GetTime()));

src/util.cpp

@@ -89,6 +89,7 @@ const int64_t nStartupTime = GetTime();
 
 const char * const BITCOIN_CONF_FILENAME = "bitcoin.conf";
 const char * const BITCOIN_PID_FILENAME = "bitcoind.pid";
+const char * const DEFAULT_DEBUGLOGFILE = "debug.log";
 
 ArgsManager gArgs;
 bool fPrintToConsole = false;
@@ -189,26 +190,40 @@ static void DebugPrintInit()
     vMsgsBeforeOpenLog = new std::list<std::string>;
 }
 
-void OpenDebugLog()
+fs::path GetDebugLogPath()
+{
+    fs::path logfile(gArgs.GetArg("-debuglogfile", DEFAULT_DEBUGLOGFILE));
+    if (logfile.is_absolute()) {
+        return logfile;
+    } else {
+        return GetDataDir() / logfile;
+    }
+}
+
+bool OpenDebugLog()
 {
     boost::call_once(&DebugPrintInit, debugPrintInitFlag);
     boost::mutex::scoped_lock scoped_lock(*mutexDebugLog);
 
     assert(fileout == nullptr);
     assert(vMsgsBeforeOpenLog);
-    fs::path pathDebug = GetDataDir() / "debug.log";
+    fs::path pathDebug = GetDebugLogPath();
+
     fileout = fsbridge::fopen(pathDebug, "a");
-    if (fileout) {
-        setbuf(fileout, nullptr); // unbuffered
-        // dump buffered messages from before we opened the log
-        while (!vMsgsBeforeOpenLog->empty()) {
-            FileWriteStr(vMsgsBeforeOpenLog->front(), fileout);
-            vMsgsBeforeOpenLog->pop_front();
-        }
+    if (!fileout) {
+        return false;
+    }
+
+    setbuf(fileout, nullptr); // unbuffered
+    // dump buffered messages from before we opened the log
+    while (!vMsgsBeforeOpenLog->empty()) {
+        FileWriteStr(vMsgsBeforeOpenLog->front(), fileout);
+        vMsgsBeforeOpenLog->pop_front();
     }
 
     delete vMsgsBeforeOpenLog;
     vMsgsBeforeOpenLog = nullptr;
+    return true;
 }
 
 struct CLogCategoryDesc
@@ -355,7 +370,7 @@ int LogPrintStr(const std::string &str)
             // reopen the log file, if requested
             if (fReopenDebugLog) {
                 fReopenDebugLog = false;
-                fs::path pathDebug = GetDataDir() / "debug.log";
+                fs::path pathDebug = GetDebugLogPath();
                 if (fsbridge::freopen(pathDebug,"a",fileout) != nullptr)
                     setbuf(fileout, nullptr); // unbuffered
             }
@@ -774,7 +789,7 @@ void ShrinkDebugFile()
     // Amount of debug.log to save at end when shrinking (must fit in memory)
     constexpr size_t RECENT_DEBUG_HISTORY_SIZE = 10 * 1000000;
     // Scroll debug.log if it's getting too big
-    fs::path pathLog = GetDataDir() / "debug.log";
+    fs::path pathLog = GetDebugLogPath();
     FILE* file = fsbridge::fopen(pathLog, "r");
     // If debug.log file is more than 10% bigger the RECENT_DEBUG_HISTORY_SIZE
     // trim it down by saving only the last RECENT_DEBUG_HISTORY_SIZE bytes

src/util.h

@@ -36,6 +36,7 @@ int64_t GetStartupTime();
 static const bool DEFAULT_LOGTIMEMICROS = false;
 static const bool DEFAULT_LOGIPS        = false;
 static const bool DEFAULT_LOGTIMESTAMPS = true;
+extern const char * const DEFAULT_DEBUGLOGFILE;
 
 /** Signals for translation. */
 class CTranslationInterface
@@ -180,7 +181,8 @@ void CreatePidFile(const fs::path &path, pid_t pid);
 #ifdef WIN32
 fs::path GetSpecialFolderPath(int nFolder, bool fCreate = true);
 #endif
-void OpenDebugLog();
+fs::path GetDebugLogPath();
+bool OpenDebugLog();
 void ShrinkDebugFile();
 void runCommand(const std::string& strCommand);