Fix syslog messages lost after syslogd restarts

If syslogd is stopped and restarted while a process has the log open, the next
message that process produces will be logged to the console and not to the new
instance of syslogd. Further messages will be routed correctly, but not the
first one.

Based on original patch
Bug 3889 - syslog loses messages when syslogd restarted
https://bugs.busybox.net/show_bug.cgi?id=3889

function                                             old     new   delta
openlog                                               33      68     +35
__vsyslog                                            851     848      -3
openlog_intern                                       318     259     -59
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/2 up/down: 35/-62)            Total: -27 bytes

Signed-off-by: Vladislav Grishenko <themiron@mail.ru>

libc/misc/syslog/syslog.c

@@ -122,23 +122,15 @@ closelog_intern(int sig)
 }
 
 static void
-openlog_intern(const char *ident, int logstat, int logfac)
+openlog_intern(void)
 {
 	int fd;
 	int logType = SOCK_DGRAM;
 
-	if (ident != NULL)
-		LogTag = ident;
-	LogStat = logstat;
-	/* (we were checking also for logfac != 0, but it breaks
-	 * openlog(xx, LOG_KERN) since LOG_KERN == 0) */
-	if ((logfac & ~LOG_FACMASK) == 0) /* if we don't have invalid bits */
-		LogFacility = (unsigned)logfac >> 3;
-
 	fd = LogFile;
 	if (fd == -1) {
  retry:
-		if (logstat & LOG_NDELAY) {
+		if (1) { /* if statement left in to make .diff cleaner */
 			LogFile = fd = socket(AF_UNIX, logType, 0);
 			if (fd == -1) {
 				return;
@@ -172,7 +164,18 @@ void
 openlog(const char *ident, int logstat, int logfac)
 {
 	__UCLIBC_MUTEX_LOCK(mylock);
-	openlog_intern(ident, logstat, logfac);
+
+	if (ident != NULL)
+		LogTag = ident;
+	LogStat = logstat;
+	/* (we were checking also for logfac != 0, but it breaks
+	 * openlog(xx, LOG_KERN) since LOG_KERN == 0) */
+	if ((logfac & ~LOG_FACMASK) == 0) /* if we don't have invalid bits */
+		LogFacility = (unsigned)logfac >> 3;
+
+	if (logstat & LOG_NDELAY)
+		openlog_intern();
+
 	__UCLIBC_MUTEX_UNLOCK(mylock);
 }
 
@@ -206,7 +209,7 @@ __vsyslog(int pri, const char *fmt, va_list ap)
 	if ((LogMask & LOG_MASK(LOG_PRI(pri))) == 0)
 		goto getout;
 	if (LogFile < 0 || !connected)
-		openlog_intern(NULL, LogStat | LOG_NDELAY, (int)LogFacility << 3);
+		openlog_intern();
 
 	/* Set default facility if none specified. */
 	if ((pri & LOG_FACMASK) == 0)
@@ -266,14 +269,23 @@ __vsyslog(int pri, const char *fmt, va_list ap)
 	/* Output the message to the local logger using NUL as a message delimiter. */
 	p = tbuf;
 	*last_chr = '\0';
+ retry:
 	if (LogFile >= 0) {
 		do {
 			/* can't just use write, it can result in SIGPIPE */
 			rc = send(LogFile, p, last_chr + 1 - p, MSG_NOSIGNAL);
 			if (rc < 0) {
-				/* I don't think looping forever on EAGAIN is a good idea.
-				 * Imagine that syslogd is SIGSTOPed... */
-				if (/* (errno != EAGAIN) && */ (errno != EINTR)) {
+				switch (errno) {
+				case EINTR:
+					break;
+				case ECONNRESET:
+					/* syslogd restarted, reopen log */
+					closelog_intern(1);
+					openlog_intern();
+					goto retry;
+				case EAGAIN:
+					/* syslogd stalled, noting we can do */
+				default:
 					closelog_intern(1); /* 1: do not reset LogXXX globals to default */
 					goto write_err;
 				}