1 files changed, 31 insertions, 6 deletions

diff --git a/src/util.h b/src/util.h
index 89dce2f..362494c 100644
--- a/src/util.h
+++ b/src/util.h
@@ -399,8 +399,11 @@ inline int OutputDebugStringF(const char* pszFormat, ...)
             else
                 strDebugFile = "debug.log";
         }
+        // Latched by a failed rename in the roll below, which cannot be
+        // retried usefully and must not be retried endlessly.
+        static bool fRollDisabled = false;
         FILE* fileout = fopen(strDebugFile.c_str(), "a");
-        if (fileout && nMaxDebugFileSize > 0)
+        if (fileout && nMaxDebugFileSize > 0 && !fRollDisabled)
         {
             // Roll an overgrown debug.log before adding to it. Nothing in the
             // tree shrinks this file once the process is running (there is no
@@ -416,12 +419,34 @@ inline int OutputDebugStringF(const char* pszFormat, ...)
                 fclose(fileout);
                 string strOldFile = strDebugFile + ".old";
                 remove(strOldFile.c_str()); // rename() won't clobber on Windows
-                rename(strDebugFile.c_str(), strOldFile.c_str());
+                bool fRolled = (rename(strDebugFile.c_str(), strOldFile.c_str()) == 0);
+                int nRenameErrno = errno; // before fopen() can overwrite it
                 fileout = fopen(strDebugFile.c_str(), "a");
-                if (fileout)
-                    fprintf(fileout,
-                        "debug.log grew past %lld MB; previous contents moved to debug.log.old (-maxdebugfilesize)\n",
-                        (long long)(nMaxDebugFileSize / 1024 / 1024));
+                if (fRolled)
+                {
+                    if (fileout)
+                        fprintf(fileout,
+                            "debug.log grew past %lld MB; previous contents moved to debug.log.old (-maxdebugfilesize)\n",
+                            (long long)(nMaxDebugFileSize / 1024 / 1024));
+                }
+                else
+                {
+                    // The file is still over the cap, so this branch would be
+                    // reached again on the next line and every line after it.
+                    // Unlatched, the complaint about failing to roll becomes
+                    // the runaway growth the roll exists to prevent. Say it
+                    // once and stop trying -- on stderr too, because whatever
+                    // blocked the rename (read-only mount, permissions, EXDEV
+                    // across a bind mount) may equally block the log write.
+                    fRollDisabled = true;
+                    fprintf(stderr,
+                        "cannot roll %s (rename to .old failed: %s); -maxdebugfilesize disabled for this run\n",
+                        strDebugFile.c_str(), strerror(nRenameErrno));
+                    if (fileout)
+                        fprintf(fileout,
+                            "cannot roll debug.log (rename to .old failed: %s); -maxdebugfilesize disabled for this run\n",
+                            strerror(nRenameErrno));
+                }
             }
         }
         if (fileout)