conf, passt: Make --stderr do nothing, and deprecate it

The original behaviour of printing messages to standard error by
default when running from a non-interactive terminal was introduced
because the first KubeVirt integration draft used to start passt in
foreground and get messages via standard error.

For development purposes, the system logger was more convenient at
that point, and passt was running from interactive terminals only if
not started by the KubeVirt integration.

This behaviour was introduced by 84a62b79a2 ("passt: Also log to
stderr, don't fork to background if not interactive").

Later, I added command-line options in 1e49d194d0 ("passt, pasta:
Introduce command-line options and port re-mapping") and accidentally
reversed this condition, which wasn't a problem as --stderr could
force printing to standard error anyway (and it was used by KubeVirt).

Nowadays, the KubeVirt integration uses a log file (requested via
libvirt configuration), and the same applies for Podman if one
actually needs to look at runtime logs. There are no use cases left,
as far as I know, where passt runs in foreground in non-interactive
terminals.

Seize the chance to reintroduce some sanity here. If we fork to
background, standard error is closed, so --stderr is useless in that
case.

If we run in foreground, there's no harm in printing messages to
standard error, and that accidentally became the default behaviour
anyway, so --stderr is not needed in that case.

It would be needed for non-interactive terminals, but there are no
use cases, and if there were, let's log to standard error anyway:
the user can always redirect standard error to /dev/null if needed.

Before we're up and running, we need to print to standard error anyway
if something happens, otherwise we can't report failure to start in
any kind of usage, stand-alone or in integrations.

So, make --stderr do nothing, and deprecate it.

While at it, drop a left-over comment about --foreground being the
default only for interactive terminals, because it's not the case
anymore.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

conf.c

@@ -727,9 +727,7 @@ static void usage(const char *name, FILE *f, int status)
 		"      --trace		Be extra verbose, implies --debug\n"
 		"  -q, --quiet		Don't print informational messages\n"
 		"  -f, --foreground	Don't run in background\n"
-		"    default: run in background if started from a TTY\n"
-		"  -e, --stderr		Log to stderr too\n"
-		"    default: log to system logger only if started from a TTY\n"
+		"    default: run in background\n"
 		"  -l, --log-file PATH	Log (only) to given file\n"
 		"  --log-size BYTES	Maximum size of log file\n"
 		"    default: 1 MiB\n"
@@ -1387,18 +1385,10 @@ void conf(struct ctx *c, int argc, char **argv)
 			c->quiet = 0;
 			break;
 		case 'e':
-			if (logfile)
-				die("Can't log to both file and stderr");
-
-			c->force_stderr = 1;
-			logfile = NULL;
+			warn("--stderr will be dropped soon");
 			break;
 		case 'l':
-			if (c->force_stderr)
-				die("Can't log to both stderr and file");
-
 			logfile = optarg;
-			c->force_stderr = 0;
 			break;
 		case 'q':
 			c->quiet = 1;
@@ -1631,9 +1621,6 @@ void conf(struct ctx *c, int argc, char **argv)
 
 	conf_ugid(runas, &uid, &gid);
 
-	if (!c->foreground && c->force_stderr)
-		die("Can't log to standard error if not running in foreground");
-
 	if (logfile) {
 		logfile_init(c->mode == MODE_PASTA ? "pasta" : "passt",
 			     logfile, logsize);

passt.1

@@ -96,21 +96,14 @@ Default is to fork into background.
 
 .TP
 .BR \-e ", " \-\-stderr
-Log to standard error too.
-Default is to log to the system logger only, if started from an interactive
-terminal, and to both system logger and standard error otherwise.
+This option has no effect, and is maintained for compatibility purposes only.
 
-This option cannot be specified together with \fB--log-file\fR, because there
-might be a reasonable expectation that messages are logged to standard error as
-well as to a file, which is however not supported.
+Note that this configuration option is \fBdeprecated\fR and will be removed in a
+future version.
 
 .TP
 .BR \-l ", " \-\-log-file " " \fIPATH\fR
-Log to file \fIPATH\fR, not to standard error, and not to the system logger.
-
-This option cannot be specified together with \fB--stderr\fR, because there
-might be a reasonable expectation that messages are logged to a file as well as
-to standard error, which is however not supported.
+Log to file \fIPATH\fR, and not to the system logger.
 
 Specifying this option multiple times does \fInot\fR lead to multiple log files:
 the last given option takes effect.

passt.c

@@ -302,7 +302,7 @@ int main(int argc, char **argv)
 	if (isolate_prefork(&c))
 		die("Failed to sandbox process, exiting");
 
-	if (!c.foreground || (!c.force_stderr && !isatty(fileno(stderr))))
+	if (!c.foreground)
 		__openlog(log_name, 0, LOG_DAEMON);
 
 	if (!c.foreground)

passt.h

@@ -180,7 +180,6 @@ struct ip6_ctx {
  * @trace:		Enable tracing (extra debug) mode
  * @quiet:		Don't print informational messages
  * @foreground:		Run in foreground, don't log to stderr by default
- * @force_stderr:	Force logging to stderr
  * @nofile:		Maximum number of open files (ulimit -n)
  * @sock_path:		Path for UNIX domain socket
  * @pcap:		Path for packet capture file
@@ -231,7 +230,6 @@ struct ctx {
 	int trace;
 	int quiet;
 	int foreground;
-	int force_stderr;
 	int nofile;
 	char sock_path[UNIX_PATH_MAX];
 	char pcap[PATH_MAX];