Re: [PATCH v2] passt, log: Call __openlog() earlier, log to stderr until we detach

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, Mar 13, 2024 at 12:58:10PM +0100, Stefano Brivio wrote:
> Paul reports that, with commit 15001b39ef1d ("conf: set the log level
> much earlier"), early messages aren't reported to standard error
> anymore.
> 
> The reason is that, once the log mask is changed from LOG_EARLY, we
> don't force logging to stderr, and this mechanism was abused to have
> early errors on stderr. Now that we drop LOG_EARLY earlier on, this
> doesn't work anymore.
> 
> Call __openlog() as soon as we know the mode we're running as, using
> LOG_PERROR. Then, once we detach, if we're not running from an
> interactive terminal and logging to standard error is not forced,
> drop LOG_PERROR from the options.
> 
> While at it, check if the standard error descriptor refers to a
> terminal, instead of checking standard output: if the user redirects
> standard output to /dev/null, they might still want to see messages
> from standard error.
> 
> Further, make sure we don't print messages to standard error reporting
> that we couldn't log to the system logger, if we didn't open a
> connection yet. That's expected.
> 
> Reported-by: Paul Holzinger <pholzing@redhat.com>
> Fixes: 15001b39ef1d ("conf: set the log level much earlier")
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
> v2: Change the isatty() test to use stderr instead of stdout
> 
>  log.c   |  2 +-
>  passt.c | 14 +++++++-------
>  2 files changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/log.c b/log.c
> index eafaca2..bdd31b4 100644
> --- a/log.c
> +++ b/log.c
> @@ -174,7 +174,7 @@ void passt_vsyslog(int pri, const char *format, va_list ap)
>  	if (log_opt & LOG_PERROR)
>  		fprintf(stderr, "%s", buf + prefix_len);
>  
> -	if (send(log_sock, buf, n, 0) != n)
> +	if (log_sock >= 0 && send(log_sock, buf, n, 0) != n)
>  		fprintf(stderr, "Failed to send %i bytes to syslog\n", n);
>  }
>  
> diff --git a/passt.c b/passt.c
> index f430648..59ab501 100644
> --- a/passt.c
> +++ b/passt.c
> @@ -225,6 +225,8 @@ int main(int argc, char **argv)
>  	strncpy(argv0, argv[0], PATH_MAX - 1);
>  	name = basename(argv0);
>  	if (strstr(name, "pasta")) {
> +		__openlog(log_name = "pasta", LOG_PERROR, LOG_DAEMON);
> +
>  		sa.sa_handler = pasta_child_handler;
>  		if (sigaction(SIGCHLD, &sa, NULL)) {
>  			die("Couldn't install signal handlers: %s",
> @@ -237,18 +239,16 @@ int main(int argc, char **argv)
>  		}
>  
>  		c.mode = MODE_PASTA;
> -		log_name = "pasta";
>  	} else if (strstr(name, "passt")) {
> +		__openlog(log_name = "passt", LOG_PERROR, LOG_DAEMON);
> +
>  		c.mode = MODE_PASST;
> -		log_name = "passt";
>  	} else {
>  		exit(EXIT_FAILURE);
>  	}
>  
>  	madvise(pkt_buf, TAP_BUF_BYTES, MADV_HUGEPAGE);
>  
> -	__openlog(log_name, 0, LOG_DAEMON);
> -
>  	c.epollfd = epoll_create1(EPOLL_CLOEXEC);
>  	if (c.epollfd == -1) {
>  		perror("epoll_create1");
> @@ -269,9 +269,6 @@ int main(int argc, char **argv)
>  	conf(&c, argc, argv);
>  	trace_init(c.trace);
>  
> -	if (c.force_stderr || isatty(fileno(stdout)))
> -		__openlog(log_name, LOG_PERROR, LOG_DAEMON);
> -
>  	pasta_netns_quit_init(&c);
>  
>  	tap_sock_init(&c);
> @@ -314,6 +311,9 @@ int main(int argc, char **argv)
>  	if (isolate_prefork(&c))
>  		die("Failed to sandbox process, exiting");
>  
> +	if (!c.force_stderr && !isatty(fileno(stderr)))
> +		__openlog(log_name, 0, LOG_DAEMON);
> +
>  	if (!c.foreground)
>  		__daemon(pidfile_fd, devnull_fd);
>  	else

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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