From a03d1fbe45f04a5fa168f40a457ebd1aa3e551f9 Mon Sep 17 00:00:00 2001
From: Simon Rose <simon.rose@ess.eu>
Date: Tue, 24 Feb 2026 13:53:14 +0000
Subject: [PATCH] Add commandline utility to resize buffer after being
 initialised

---
 modules/libcom/src/error/errlog.c         | 29 +++++++++++++++++++++++
 modules/libcom/src/error/errlog.h         |  9 +++++++
 modules/libcom/src/iocsh/libComRegister.c | 17 +++++++++++++
 3 files changed, 55 insertions(+)

diff --git a/modules/libcom/src/error/errlog.c b/modules/libcom/src/error/errlog.c
index 3aff8e2ec..b5678fcba 100644
--- a/modules/libcom/src/error/errlog.c
+++ b/modules/libcom/src/error/errlog.c
@@ -77,6 +77,7 @@ typedef struct {
 } buffer_t;
 
 static struct {
+    epicsMutexId bufSizeLock;
     /* const after errlogInit() */
     size_t maxMsgSize;
     /* alloc size of both buffer_t::base */
@@ -548,6 +549,7 @@ static void errlogInitPvt(void *arg)
      */
 
     pvt.errlogInitFailed = TRUE;
+    pvt.bufSizeLock = epicsMutexCreate();
     pvt.bufSize = pconfig->bufsize;
     pvt.maxMsgSize = pconfig->maxMsgSize;
     ellInit(&pvt.listenerList);
@@ -566,6 +568,7 @@ static void errlogInitPvt(void *arg)
     errSymBld();    /* Better not to do this lazily... */
 
     if(pvt.waitForWork
+            && pvt.bufSizeLock
             && pvt.listenerLock
             && pvt.msgQueueLock
             && pvt.waitForSeq
@@ -612,6 +615,32 @@ int errlogInit(int bufsize)
     return errlogInit2(bufsize, DEFAULT_MAX_MSG_SIZE);
 }
 
+void errlogBufResize(int bufsize, int maxMsgSize)
+{
+    if (bufsize < MIN_BUFFER_SIZE)
+        bufsize = MIN_BUFFER_SIZE;
+    if (maxMsgSize < MIN_MESSAGE_SIZE)
+        maxMsgSize = MIN_MESSAGE_SIZE;
+    else if (maxMsgSize > MAX_MESSAGE_SIZE)
+        maxMsgSize = MAX_MESSAGE_SIZE;
+
+    errlogFlush();
+
+    epicsMutexMustLock(pvt.bufSizeLock);
+    epicsMutexMustLock(pvt.msgQueueLock);
+
+    pvt.bufSize = bufsize;
+    pvt.maxMsgSize = maxMsgSize;
+
+    free(pvt.log->base);
+    pvt.log->base = callocMustSucceed(1, pvt.bufSize, "Failed to allocate memory for errorlog buffer");
+    free(pvt.print->base);
+    pvt.print->base = callocMustSucceed(1, pvt.bufSize, "Failed to allocate memory for errorlog buffer");
+
+    epicsMutexUnlock(pvt.msgQueueLock);
+    epicsMutexUnlock(pvt.bufSizeLock);
+}
+
 void errlogFlush(void)
 {
     /* wait for both buffers to be handled to know that all currently
diff --git a/modules/libcom/src/error/errlog.h b/modules/libcom/src/error/errlog.h
index a204bec87..aea8437da 100644
--- a/modules/libcom/src/error/errlog.h
+++ b/modules/libcom/src/error/errlog.h
@@ -224,6 +224,15 @@ LIBCOM_API int errlogInit(int bufsize);
  */
 LIBCOM_API int errlogInit2(int bufsize, int maxMsgSize);
 
+/**
+ * errlogBufResize can be used to reinitialize the error logging system with a larger buffer and maximum message size.
+ * The default buffer size is 1280 bytes, and the default maximum message size is 256.
+ *
+ * \param bufsize The desired buffer size
+ * \param maxMsgSize The desired max message size
+ */
+LIBCOM_API void errlogBufResize(int bufsize, int maxMsgSize);
+
 /** Wakes up the errlog task and then waits until all messages are flushed from the queue. */
 LIBCOM_API void errlogFlush(void);
 
diff --git a/modules/libcom/src/iocsh/libComRegister.c b/modules/libcom/src/iocsh/libComRegister.c
index 709452473..844ee14e2 100644
--- a/modules/libcom/src/iocsh/libComRegister.c
+++ b/modules/libcom/src/iocsh/libComRegister.c
@@ -290,6 +290,22 @@ static void errlogInit2CallFunc(const iocshArgBuf *args)
     errlogInit2(args[0].ival, args[1].ival);
 }
 
+/* errlogBufResize */
+static const iocshArg errlogBufResizeArg0 = { "bufSize",iocshArgInt};
+static const iocshArg errlogBufResizeArg1 = { "maxMsgSize",iocshArgInt};
+static const iocshArg * const errlogBufResizeArgs[] =
+    {&errlogBufResizeArg0, &errlogBufResizeArg1};
+static const iocshFuncDef errlogBufResizeFuncDef = {
+    "errlogBufResize", 2, errlogBufResizeArgs,
+    "Reinitialize error log client buffer size and maximum message size\n"
+    "  bufSize    - size of circular buffer       (default = 1280 bytes)\n"
+    "  maxMsgSize - maximum size of error message (default =  256 bytes)\n"
+};
+static void errlogBufResizeCallFunc(const iocshArgBuf *args)
+{
+    errlogBufResize(args[0].ival, args[1].ival);
+}
+
 /* errlog */
 IOCSH_STATIC_FUNC void errlog(const char *message)
 {
@@ -500,6 +516,7 @@ void epicsStdCall libComRegister(void)
     iocshRegister(&eltcFuncDef, eltcCallFunc);
     iocshRegister(&errlogInitFuncDef,errlogInitCallFunc);
     iocshRegister(&errlogInit2FuncDef,errlogInit2CallFunc);
+    iocshRegister(&errlogBufResizeFuncDef,errlogBufResizeCallFunc);
     iocshRegister(&errlogFuncDef, errlogCallFunc);
     iocshRegister(&iocLogPrefixFuncDef, iocLogPrefixCallFunc);