imkmsg: add params "readMode" and "expectedBootCompleteSeconds"

These parameters permit to control when imkmsg reads the full
kernel log upon startup.

Parameter "readMode" provides the following options:

  * full-boot - (default) read full klog, but only "immediately" after
    boot. "Immediately" is hereby meant in seconds of system
    uptime given in "expectedBootCompleteSeconds"
  * full-always - read full klog on every rsyslog startup. Most
    probably causes messag duplication
  * new-only - never emit existing kernel log message, read only
    new ones.

Note that some message loss can happen if rsyslog is stopped
in "full-boot" and "new-only" read mode. The longer rsyslog is
inactive, the higher the message loss probability and potential
number of messages lost. For typical restart scenarios, this
should be minimal. On HUP, no message loss occurs as rsyslog
is not actually stopped.

The default value for "expectedBootCompleteSeconds" is 90.

see also #5161

contrib/imkmsg/imkmsg.c

@@ -72,7 +72,9 @@ static int bLegacyCnfModGlobalsPermitted;/* are legacy module-global config para
 
 /* module-global parameters */
 static struct cnfparamdescr modpdescr[] = {
-	{ "parsekerneltimestamp", eCmdHdlrGetWord, 0 }
+	{ "parsekerneltimestamp", eCmdHdlrGetWord, 0 },
+	{ "readmode", eCmdHdlrGetWord, 0 },
+	{ "expectedbootcompleteseconds", eCmdHdlrPositiveInt, 0 }
 };
 static struct cnfparamblk modpblk =
 	{ CNFPARAMBLK_VERSION,
@@ -193,6 +195,8 @@ CODESTARTbeginCnfLoad
 	/* init our settings */
 	pModConf->iFacilIntMsg = klogFacilIntMsg();
 	pModConf->parseKernelStamp = KMSG_PARSE_TS_STARTUP_ONLY;
+	pModConf->readMode = KMSG_READMODE_FULL_BOOT;
+	pModConf->expected_boot_complete_secs = 90;
 	loadModConf->configSetViaV2Method = 0;
 	bLegacyCnfModGlobalsPermitted = 1;
 	/* init legacy config vars */
@@ -233,6 +237,21 @@ CODESTARTsetModCnf
 					"parse mode '%s'", cstr);
 				free((void*)cstr);
 			}
+		} else if(!strcmp(modpblk.descr[i].name, "expectedbootcompleteseconds")) {
+				loadModConf->expected_boot_complete_secs = pvals[i].val.d.n;
+		} else if(!strcmp(modpblk.descr[i].name, "readmode")) {
+			if(!es_strconstcmp(pvals[i].val.d.estr, "full-boot")) {
+				loadModConf->readMode = KMSG_READMODE_FULL_BOOT;
+			} else if(!es_strconstcmp(pvals[i].val.d.estr, "full-always")) {
+				loadModConf->readMode = KMSG_READMODE_FULL_ALWAYS;
+			} else if(!es_strconstcmp(pvals[i].val.d.estr, "new-only")) {
+				loadModConf->readMode = KMSG_READMODE_NEW_ONLY;
+			} else {
+				const char *const cstr = es_str2cstr(pvals[i].val.d.estr, NULL);
+				LogError(0, RS_RET_PARAM_ERROR, "imkmsg: unknown "
+					"read mode '%s', keeping default setting", cstr);
+				free((void*)cstr);
+			}
 		} else {
 			LogMsg(0, RS_RET_INTERNAL_ERROR, LOG_WARNING,
 				"imkmsg: RSYSLOG BUG, non-handled param '%s' in "

contrib/imkmsg/imkmsg.h

@@ -31,14 +31,21 @@ typedef enum _kernel_ts_parse_mods {
 		KMSG_PARSE_TS_STARTUP_ONLY = 2
 	} t_kernel_ts_parse_mode;
 
+typedef enum _kernel_readmode {
+		KMSG_READMODE_FULL_BOOT = 0,
+		KMSG_READMODE_FULL_ALWAYS = 1,
+		KMSG_READMODE_NEW_ONLY = 2
+	} t_kernel_readmode;
+
 /* we need to have the modConf type present in all submodules */
 struct modConfData_s {
 	rsconf_t *pConf;
 	int iFacilIntMsg;
 	uchar *pszPath;
 	int console_log_level;
+	int expected_boot_complete_secs;
 	t_kernel_ts_parse_mode parseKernelStamp;
-	sbool bFixKernelStamp;
+	t_kernel_readmode readMode;
 	sbool configSetViaV2Method;
 };
 

contrib/imkmsg/kmsg.c

@@ -228,8 +228,31 @@ static void
 readkmsg(modConfData_t *const pModConf)
 {
 	int i;
-	uchar pRcv[8192+1];
+	uchar pRcv[16*1024+1];
 	char errmsg[2048];
+	off_t seek_result = 0;
+
+	if(pModConf->readMode == KMSG_READMODE_FULL_BOOT) {
+		struct sysinfo info;
+		sysinfo(&info);
+		DBGPRINTF("imkmsg: system uptime is %lld, expected %d\n",
+			(long long) info.uptime, pModConf->expected_boot_complete_secs);
+		if(info.uptime > pModConf->expected_boot_complete_secs) {
+			seek_result = lseek(fklog, 0, SEEK_END);
+		}
+	} else if(pModConf->readMode == KMSG_READMODE_NEW_ONLY) {
+		seek_result = lseek(fklog, 0, SEEK_END);
+	} else if(pModConf->readMode != KMSG_READMODE_FULL_ALWAYS) {
+		imkmsgLogIntMsg(LOG_ERR, "imkmsg: internal program error, "
+				"unknown read mode %d, assuming 'full-always'",
+				pModConf->readMode);
+	}
+
+	if(seek_result == (off_t) -1) {
+		imkmsgLogIntMsg(LOG_WARNING,
+				"imkmsg: could not seek to requested klog entries - will"
+				"now potentially output all messages");
+	}
 
 	for (;;) {
 		dbgprintf("imkmsg waiting for kernel log line\n");