On Fri, Dec 13, 2019 at 12:42:03PM +0100, Alex Gladkov wrote:
> diff --git a/hasher-priv/logging.c b/hasher-priv/logging.c
> new file mode 100644
> index 0000000..9adac47
> --- /dev/null
> +++ b/hasher-priv/logging.c
> @@ -0,0 +1,64 @@
> +
> +/*
> +  Copyright (C) 2019  Alexey Gladkov <legion@altlinux.org>
> +
> +  A logging functions for the hasher-privd program.
> +
> +  SPDX-License-Identifier: GPL-2.0-or-later
> +*/
> +
> +#include <stdio.h>
> +#include <stdarg.h>
> +#include <strings.h>
> +#include <errno.h>
> +#include <syslog.h>
> +
> +#include "logging.h"
> +
> +int log_priority = -1;
> +
> +int logging_level(const char *name)
> +{
> +	if (!strcasecmp(name, "debug"))
> +		return LOG_DEBUG;
> +
> +	if (!strcasecmp(name, "info"))
> +		return LOG_INFO;
> +
> +	if (!strcasecmp(name, "warning"))
> +		return LOG_WARNING;
> +
> +	if (!strcasecmp(name, "error"))
> +		return LOG_ERR;
> +
> +	return 0;
> +}
> +
> +void logging_init(int loglevel, int stderr)
> +{
> +	int options = LOG_PID;
> +	if (stderr)
> +		options |= LOG_PERROR;
> +	log_priority = loglevel;
> +	openlog(program_invocation_short_name, options, LOG_DAEMON);
> +}
> +
> +void logging_close(void)
> +{
> +	closelog();
> +}
> +
> +void
> +message(int priority, const char *fmt, ...)
> +{
> +	va_list ap;
> +
> +	va_start(ap, fmt);
> +	if (priority <= log_priority)
> +		vsyslog(priority, fmt, ap);

If the daemon is invoked with `-f', why not log to stderr only,
prepending the message priority? That behaviour would fit better with
service managers that take care of process daemonization / pid tracking
themselves and direct the service's stderr to system log.

If log message duplication is desired, we can add a command line
argument to enforce that.

To produce messages of different priorities, we can prepend "<%d>" to
each log message.

> +	else if (log_priority < 0) {
> +		vfprintf(stderr, fmt, ap);
> +		fprintf(stderr, "\n");
> +	}
> +	va_end(ap);
> +}
> diff --git a/hasher-priv/logging.h b/hasher-priv/logging.h
> new file mode 100644
> index 0000000..9d28fc8
> --- /dev/null
> +++ b/hasher-priv/logging.h
> @@ -0,0 +1,55 @@
> +
> +/*
> +  Copyright (C) 2019  Alexey Gladkov <legion@altlinux.org>
> +
> +  A logging functions for the hasher-privd program.
> +
> +  SPDX-License-Identifier: GPL-2.0-or-later
> +*/
> +
> +#ifndef _LOGGING_H_
> +#define _LOGGING_H_
> +
> +#include <syslog.h>
> +#include <stdlib.h>
> +
> +void logging_init(int, int);
> +void logging_close(void);
> +int logging_level(const char *lvl) __attribute__((nonnull(1)));
> +
> +void message(int priority, const char *fmt, ...) __attribute__((format(printf, 2, 3)));
> +
> +#define fatal(format, arg...)                             \
> +	do {                                              \
> +		message(LOG_CRIT,                         \
> +		        "%s(%d): %s: " format,            \
> +		        __FILE__, __LINE__, __FUNCTION__, \
> +		        ##arg);                           \
> +		exit(EXIT_FAILURE);                       \
> +	} while (0)
> +
> +#define err(format, arg...)                               \
> +	do {                                              \
> +		message(LOG_ERR,                          \
> +		        "%s(%d): %s: " format,            \
> +		        __FILE__, __LINE__, __FUNCTION__, \
> +		        ##arg);                           \
> +	} while (0)
> +
> +#define info(format, arg...)                              \
> +	do {                                              \
> +		message(LOG_INFO,                         \
> +		        "%s(%d): %s: " format,            \
> +		        __FILE__, __LINE__, __FUNCTION__, \
> +		        ##arg);                           \
> +	} while (0)
> +
> +#define dbg(format, arg...)                               \
> +	do {                                              \
> +		message(LOG_DEBUG,                        \
> +		        "%s(%d): %s: " format,            \
> +		        __FILE__, __LINE__, __FUNCTION__, \
> +		        ##arg);                           \
> +	} while (0)
> +
> +#endif /* _LOGGING_H_ */