Re: [PATCH v4 1/9] log to stderr until process is daemonized, even if a log file is set

[Stefano Brivio <sbrivio@redhat.com>]

On Wed, 15 Feb 2023 03:24:29 -0500
Laine Stump <laine@redhat.com> wrote:

> Once a log file (specified on the commandline) is opened, the logging
> functions will stop sending error logs to stderr, which is annoying if
> passt has been started by another process that wants to collect error
> messages from stderr so it can report why passt failed to start. It
> would be much nicer if passt continued sending all log messages to
> stderr until it daemonizes itself (at which point the process that
> started passt can assume that it was started successfully).
> 
> The system log mask is set to LOG_EMERG when the process starts, and
> we're already using that to do "special" logging during the period
> from process start until the log level requested on the commandline is
> processed (setting the log mask to something else). This period
> *almost* matches with "the time before the process is daemonized"; if
> we just delay setting the log mask a tiny bit, then it will match
> exactly, and we can use it to determine if we need to send log
> messages to stderr even when a log file has been specified and opened.
> 
> This patch delays the setting of the log mask until immediately before
> the call to __daemon(). It also modifies logfn() slightly, so that it
> will log to stderr any time log mask is LOG_EMERG, even if a log file
> has been opened.
> 
> Signed-off-by: Laine Stump <laine@redhat.com>
> ---
>  log.c   |  4 ++--
>  passt.c | 17 ++++++++++-------
>  2 files changed, 12 insertions(+), 9 deletions(-)
> 
> diff --git a/log.c b/log.c
> index 468c730..6dc6673 100644
> --- a/log.c
> +++ b/log.c
> @@ -66,8 +66,8 @@ void name(const char *format, ...) {					\
>  		va_end(args);						\
>  	}								\
>  									\
> -	if ((setlogmask(0) & LOG_MASK(LOG_DEBUG) ||			\
> -	     setlogmask(0) == LOG_MASK(LOG_EMERG)) && log_file == -1) {	\
> +	if ((setlogmask(0) & LOG_MASK(LOG_DEBUG) && log_file == -1) ||	\
> +	     setlogmask(0) == LOG_MASK(LOG_EMERG)) {			\
>  		va_start(args, format);					\
>  		(void)vfprintf(stderr, format, args); 			\
>  		va_end(args);						\

Strictly speaking, I think this is correct, but it causes duplicate
messages to be printed on interactive terminals, or with -e/--stderr,
because in that case we already set LOG_PERROR in our __openlog()
wrapper.

I had a quick attempt at reworking this whole mess, with a table
clearly gathering conditions and logging outcomes, but it's actually
not that straightforward.

So I'd rather just post a follow-up patch for this, at least for the
moment.

-- 
Stefano