log: introduce "none" logging backendbg/log-none

In initrd, the NM service should write logs to both the active console
and the journal. To achieve that, NetworkManager is started with
"--debug" to output logs to stderr, and the systemd unit is configured
with "StandardError=tty" to redirect messages to the console. NM is
configured with "logging.backend=journal" to also save logs in the
journal. The problem of this approach is that when the system doesn't
have a console, the NM service fails to start [1].

This can be solved by using "StandardError=journal+console" which
forwards messages from stderr to journald (which in turn also writes
them to the console if available). To avoid duplicates entries in the
journal, we need a way to disable all logging backends in NM and only
write to stderr.

Introduce a "none" logging backend. Of course, it's not recommended to
start NM without logging; therefore the "none" backend can't be used
as build-time default. "none" only makes some sense when also starting
NM with "--debug".

[1] https://github.com/coreos/fedora-coreos-tracker/issues/943

3 files changed, 18 insertions, 7 deletions

diff --git a/man/NetworkManager.conf.xml b/man/NetworkManager.conf.xml
index 7eaa4cb2a1..1ebeaabaf4 100644
--- a/man/NetworkManager.conf.xml
+++ b/man/NetworkManager.conf.xml
@@ -717,11 +717,13 @@ unmanaged-devices=mac:00:22:68:1c:59:b1;mac:00:1E:65:30:D1:C4;interface-name:eth
         </varlistentry>
         <varlistentry>
           <term><varname>backend</varname></term>
-          <listitem><para>The logging backend. Supported values
-          are "<literal>syslog</literal>" and "<literal>journal</literal>".
-          When NetworkManager is started with "<literal>--debug</literal>"
-          in addition all messages will be printed to stderr.
-          If unspecified, the default is "<literal>&NM_CONFIG_DEFAULT_LOGGING_BACKEND_TEXT;</literal>".
+          <listitem><para>The logging backend. Supported values are
+          "<literal>syslog</literal>", "<literal>journal</literal>"
+          and "<literal>none</literal>".  When NetworkManager is
+          started with "<literal>--debug</literal>" in addition all
+          messages will be printed to stderr.  If unspecified, the
+          default is
+          "<literal>&NM_CONFIG_DEFAULT_LOGGING_BACKEND_TEXT;</literal>".
           </para></listitem>
         </varlistentry>
         <varlistentry>
diff --git a/src/libnm-log-core/nm-logging.c b/src/libnm-log-core/nm-logging.c
index 6d2c085eee..da82cd0238 100644
--- a/src/libnm-log-core/nm-logging.c
+++ b/src/libnm-log-core/nm-logging.c
@@ -75,6 +75,7 @@ G_STATIC_ASSERT(sizeof(NMLogDomain) >= sizeof(guint64));
 /*****************************************************************************/
 
 typedef enum {
+    LOG_BACKEND_NONE,
     LOG_BACKEND_GLIB,
     LOG_BACKEND_SYSLOG,
     LOG_BACKEND_JOURNAL,
@@ -794,6 +795,8 @@ _nm_log_impl(const char *file,
     case LOG_BACKEND_SYSLOG:
         syslog(nm_log_level_desc[level].syslog_level, MESSAGE_FMT, MESSAGE_ARG(g->prefix, tv, msg));
         break;
+    case LOG_BACKEND_NONE:
+        break;
     default:
         g_log(syslog_identifier_domain(g->syslog_identifier),
               nm_log_level_desc[level].g_log_level,
@@ -867,6 +870,8 @@ nm_log_handler(const char *log_domain, GLogLevelFlags level, const char *message
         g_printerr("%s%s\n", gl.imm.prefix, message ?: "");
 
     switch (gl.imm.log_backend) {
+    case LOG_BACKEND_NONE:
+        break;
 #if SYSTEMD_JOURNAL
     case LOG_BACKEND_JOURNAL:
     {
@@ -980,8 +985,11 @@ nm_logging_init(const char *logging_backend, gboolean debug)
 
     G_LOCK(log);
 
+    if (nm_streq(logging_backend, NM_LOG_CONFIG_BACKEND_NONE)) {
+        x_log_backend = LOG_BACKEND_NONE;
+    } else
 #if SYSTEMD_JOURNAL
-    if (!nm_streq(logging_backend, NM_LOG_CONFIG_BACKEND_SYSLOG)) {
+        if (!nm_streq(logging_backend, NM_LOG_CONFIG_BACKEND_SYSLOG)) {
         x_log_backend = LOG_BACKEND_JOURNAL;
 
         /* We only log the monotonic-timestamp with structured logging (journal).
@@ -1017,7 +1025,7 @@ nm_logging_init(const char *logging_backend, gboolean debug)
                    "config: ignore deprecated logging backend 'debug', fallback to '%s'",
                    logging_backend);
 
-    if (nm_streq(logging_backend, NM_LOG_CONFIG_BACKEND_SYSLOG)) {
+    if (NM_IN_STRSET(logging_backend, NM_LOG_CONFIG_BACKEND_SYSLOG, NM_LOG_CONFIG_BACKEND_NONE)) {
         /* good */
     } else if (nm_streq(logging_backend, NM_LOG_CONFIG_BACKEND_JOURNAL)) {
 #if !SYSTEMD_JOURNAL
diff --git a/src/libnm-log-core/nm-logging.h b/src/libnm-log-core/nm-logging.h
index 8071967552..739473a1ad 100644
--- a/src/libnm-log-core/nm-logging.h
+++ b/src/libnm-log-core/nm-logging.h
@@ -16,6 +16,7 @@
 #define NM_LOG_CONFIG_BACKEND_DEBUG   "debug"
 #define NM_LOG_CONFIG_BACKEND_SYSLOG  "syslog"
 #define NM_LOG_CONFIG_BACKEND_JOURNAL "journal"
+#define NM_LOG_CONFIG_BACKEND_NONE    "none"
 
 #define nm_log_err(domain, ...)   nm_log(LOGL_ERR, (domain), NULL, NULL, __VA_ARGS__)
 #define nm_log_warn(domain, ...)  nm_log(LOGL_WARN, (domain), NULL, NULL, __VA_ARGS__)