log: cap debug.log in-process, and ship a logrotate policy

debug.log grew without bound (production: 1.95 GiB, 51-129 MB/day).
Nothing shrank it once the process was up -- there is no
ShrinkDebugFile in this tree, and upstream's only ran at startup.

OutputDebugStringF now rolls the file to debug.log.old when it
passes -maxdebugfilesize (MB, default 1024, 0 disables). The write
path already opens and closes the file per line under one lock, so
the rename-and-reopen is a few lines inside that lock and no fd can
be stranded mid-roll.

contrib/logrotate/bitflash-debug.logrotate is the longer-term policy
(size 1G, rotate 4, compress, missingok, notifempty, copytruncate);
copytruncate keeps the writer's append handle valid across rotation.

Closes #34

1 files changed, 15 insertions, 0 deletions

diff --git a/src/main_gui.cpp b/src/main_gui.cpp
index 211e1e2..05f5ecf 100644
--- a/src/main_gui.cpp
+++ b/src/main_gui.cpp
@@ -111,6 +111,7 @@ static void PrintUsage()
     printf("  /help, -help, --help, /?\n");
     printf("  /datadir=PATH\n");
     printf("  /debug\n");
+    printf("  /maxdebugfilesize=N        (roll debug.log at N MB, default 1024; 0 = never)\n");
     printf("  /gen\n");
     printf("  /nogui or /daemon\n");
     printf("  /selftest=wallet-keypool, wallet-hd, wallet-format, wallet-crypto, wallet-encrypt,\n");
@@ -191,6 +192,20 @@ static void ParseStartupArguments(int argc, char* argv[])
     if (arg(argc,argv,"/debug") || arg(argc,argv,"-debug"))
         fDebug = true;
 
+    // /maxdebugfilesize=N -- roll debug.log to debug.log.old once it passes
+    // N MB, checked on each write. Default is 1024 (see util.cpp); 0 turns
+    // the check off and leaves rotation entirely to logrotate.
+    string strMaxDebugSize = argval2(argc, argv, "/maxdebugfilesize", "-maxdebugfilesize");
+    if (!strMaxDebugSize.empty())
+    {
+        int64 nMB = atoi64(strMaxDebugSize.c_str());
+        if (nMB < 0)
+            fprintf(stderr, "Ignoring /maxdebugfilesize=%s: not a size in MB\n",
+                    strMaxDebugSize.c_str());
+        else
+            nMaxDebugFileSize = nMB * 1024 * 1024;
+    }
+
     if (arg(argc,argv,"/gen") || arg(argc,argv,"-gen"))
     {
         fGenerateBitcoins = 1;