Optionally re-introduce bb_info_msg()

Between Busybox 1.24.2 and 1.25.0 the bb_info_msg() function was
eliminated and calls to it changed to be bb_error_msg(). The downside of
this is that daemons now log all messages to syslog at the LOG_ERR level
which makes it hard to filter errors from informational messages.

This change optionally re-introduces bb_info_msg(), controlled by a new
option FEATURE_SYSLOG_INFO, restores all the calls to bb_info_msg() that
were removed (only in applets that set logmode to LOGMODE_SYSLOG or
LOGMODE_BOTH), and also changes informational messages in ifplugd and
ntpd.

The code size change of this is as follows (using 'defconfig' on x86_64
with gcc 7.3.0-27ubuntu1~18.04)

function                                             old     new   delta
bb_info_msg                                            -     182    +182
bb_vinfo_msg                                           -      27     +27
static.log7                                          194     198      +4
log8                                                 190     191      +1
log5                                                 190     191      +1
crondlog                                              45       -     -45
------------------------------------------------------------------------------
(add/remove: 2/1 grow/shrink: 3/0 up/down: 215/-45)           Total: 170 bytes

If you don't care about everything being logged at LOG_ERR level
then when FEATURE_SYSLOG_INFO is disabled Busybox actually gets smaller:

function                                             old     new   delta
static.log7                                          194     200      +6
log8                                                 190     193      +3
log5                                                 190     193      +3
syslog_level                                           1       -      -1
bb_verror_msg                                        583     581      -2
crondlog                                              45       -     -45
------------------------------------------------------------------------------
(add/remove: 0/2 grow/shrink: 3/1 up/down: 12/-48)            Total: -36 bytes

Signed-off-by: James Byrne <james.byrne@origamienergy.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 20 insertions, 2 deletions

diff --git a/libbb/verror_msg.c b/libbb/verror_msg.c
index 22c30357b..6d3459905 100644
--- a/libbb/verror_msg.c
+++ b/libbb/verror_msg.c
@@ -12,7 +12,7 @@
 #endif
 
 #if ENABLE_FEATURE_SYSLOG
-smallint syslog_level = LOG_ERR;
+static smallint syslog_level = LOG_ERR;
 #endif
 smallint logmode = LOGMODE_STDIO;
 const char *msg_eol = "\n";
@@ -154,7 +154,7 @@ void FAST_FUNC bb_verror_msg(const char *s, va_list p, const char* strerr)
         }
 # if ENABLE_FEATURE_SYSLOG
         if (logmode & LOGMODE_SYSLOG) {
-                syslog(LOG_ERR, "%s", msgc);
+                syslog(syslog_level, "%s", msgc);
         }
 # endif
         free(msgc);
@@ -180,3 +180,21 @@ void FAST_FUNC bb_error_msg(const char *s, ...)
         bb_verror_msg(s, p, NULL);
         va_end(p);
 }
+
+#if ENABLE_FEATURE_SYSLOG_INFO
+void FAST_FUNC bb_vinfo_msg(const char *s, va_list p)
+{
+        syslog_level = LOG_INFO;
+        bb_verror_msg(s, p, NULL);
+        syslog_level = LOG_ERR;
+}
+
+void FAST_FUNC bb_info_msg(const char *s, ...)
+{
+        va_list p;
+
+        va_start(p, s);
+        bb_vinfo_msg(s, p);
+        va_end(p);
+}
+#endif