[thirdparty/systemd.git] / src / basic / log.c

/* SPDX-License-Identifier: LGPL-2.1+ */

#include <errno.h>
#include <fcntl.h>
#include <inttypes.h>
#include <limits.h>
#include <stdarg.h>
#include <stddef.h>
#include <stdio.h>
#include <string.h>
#include <sys/signalfd.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <sys/uio.h>
#include <sys/un.h>
#include <time.h>
#include <unistd.h>

#include "sd-messages.h"

#include "alloc-util.h"
#include "fd-util.h"
#include "format-util.h"
#include "io-util.h"
#include "log.h"
#include "macro.h"
#include "missing.h"
#include "parse-util.h"
#include "proc-cmdline.h"
#include "process-util.h"
#include "signal-util.h"
#include "socket-util.h"
#include "stdio-util.h"
#include "string-table.h"
#include "string-util.h"
#include "syslog-util.h"
#include "terminal-util.h"
#include "time-util.h"
#include "utf8.h"
#include "util.h"

#define SNDBUF_SIZE (8*1024*1024)

static LogTarget log_target = LOG_TARGET_CONSOLE;
static int log_max_level[] = {LOG_INFO, LOG_INFO};
assert_cc(ELEMENTSOF(log_max_level) == _LOG_REALM_MAX);
static int log_facility = LOG_DAEMON;

static int console_fd = STDERR_FILENO;
static int syslog_fd = -1;
static int kmsg_fd = -1;
static int journal_fd = -1;

static bool syslog_is_stream = false;

static bool show_color = false;
static bool show_location = false;

static bool upgrade_syslog_to_journal = false;
static bool always_reopen_console = false;
static bool open_when_needed = false;
static bool prohibit_ipc = false;

/* Akin to glibc's __abort_msg; which is private and we hence cannot
 * use here. */
static char *log_abort_msg = NULL;

/* An assert to use in logging functions that does not call recursively
 * into our logging functions (since that might lead to a loop). */
#define assert_raw(expr)                                                \
        do {                                                            \
                if (_unlikely_(!(expr))) {                              \
                        fputs(#expr "\n", stderr);                      \
                        abort();                                        \
                }                                                       \
        } while (false)

static void log_close_console(void) {
        console_fd = safe_close_above_stdio(console_fd);
}

static int log_open_console(void) {

        if (!always_reopen_console) {
                console_fd = STDERR_FILENO;
                return 0;
        }

        if (console_fd < 3) {
                console_fd = open_terminal("/dev/console", O_WRONLY|O_NOCTTY|O_CLOEXEC);
                if (console_fd < 0)
                        return console_fd;

                console_fd = fd_move_above_stdio(console_fd);
        }

        return 0;
}

static void log_close_kmsg(void) {
        kmsg_fd = safe_close(kmsg_fd);
}

static int log_open_kmsg(void) {

        if (kmsg_fd >= 0)
                return 0;

        kmsg_fd = open("/dev/kmsg", O_WRONLY|O_NOCTTY|O_CLOEXEC);
        if (kmsg_fd < 0)
                return -errno;

        kmsg_fd = fd_move_above_stdio(kmsg_fd);
        return 0;
}

static void log_close_syslog(void) {
        syslog_fd = safe_close(syslog_fd);
}

static int create_log_socket(int type) {
        struct timeval tv;
        int fd;

        fd = socket(AF_UNIX, type|SOCK_CLOEXEC, 0);
        if (fd < 0)
                return -errno;

        fd = fd_move_above_stdio(fd);
        (void) fd_inc_sndbuf(fd, SNDBUF_SIZE);

        /* We need a blocking fd here since we'd otherwise lose messages way too early. However, let's not hang forever
         * in the unlikely case of a deadlock. */
        if (getpid_cached() == 1)
                timeval_store(&tv, 10 * USEC_PER_MSEC);
        else
                timeval_store(&tv, 10 * USEC_PER_SEC);
        (void) setsockopt(fd, SOL_SOCKET, SO_SNDTIMEO, &tv, sizeof(tv));

        return fd;
}

static int log_open_syslog(void) {

        static const union sockaddr_union sa = {
                .un.sun_family = AF_UNIX,
                .un.sun_path = "/dev/log",
        };

        int r;

        if (syslog_fd >= 0)
                return 0;

        syslog_fd = create_log_socket(SOCK_DGRAM);
        if (syslog_fd < 0) {
                r = syslog_fd;
                goto fail;
        }

        if (connect(syslog_fd, &sa.sa, SOCKADDR_UN_LEN(sa.un)) < 0) {
                safe_close(syslog_fd);

                /* Some legacy syslog systems still use stream
                 * sockets. They really shouldn't. But what can we
                 * do... */
                syslog_fd = create_log_socket(SOCK_STREAM);
                if (syslog_fd < 0) {
                        r = syslog_fd;
                        goto fail;
                }

                if (connect(syslog_fd, &sa.sa, SOCKADDR_UN_LEN(sa.un)) < 0) {
                        r = -errno;
                        goto fail;
                }

                syslog_is_stream = true;
        } else
                syslog_is_stream = false;

        return 0;

fail:
        log_close_syslog();
        return r;
}

static void log_close_journal(void) {
        journal_fd = safe_close(journal_fd);
}

static int log_open_journal(void) {

        static const union sockaddr_union sa = {
                .un.sun_family = AF_UNIX,
                .un.sun_path = "/run/systemd/journal/socket",
        };

        int r;

        if (journal_fd >= 0)
                return 0;

        journal_fd = create_log_socket(SOCK_DGRAM);
        if (journal_fd < 0) {
                r = journal_fd;
                goto fail;
        }

        if (connect(journal_fd, &sa.sa, SOCKADDR_UN_LEN(sa.un)) < 0) {
                r = -errno;
                goto fail;
        }

        return 0;

fail:
        log_close_journal();
        return r;
}

int log_open(void) {
        int r;

        /* Do not call from library code. */

        /* If we don't use the console we close it here, to not get
         * killed by SAK. If we don't use syslog we close it here so
         * that we are not confused by somebody deleting the socket in
         * the fs, and to make sure we don't use it if prohibit_ipc is
         * set. If we don't use /dev/kmsg we still keep it open,
         * because there is no reason to close it. */

        if (log_target == LOG_TARGET_NULL) {
                log_close_journal();
                log_close_syslog();
                log_close_console();
                return 0;
        }

        if (log_target != LOG_TARGET_AUTO ||
            getpid_cached() == 1 ||
            isatty(STDERR_FILENO) <= 0) {

                if (!prohibit_ipc &&
                    IN_SET(log_target, LOG_TARGET_AUTO,
                                       LOG_TARGET_JOURNAL_OR_KMSG,
                                       LOG_TARGET_JOURNAL)) {
                        r = log_open_journal();
                        if (r >= 0) {
                                log_close_syslog();
                                log_close_console();
                                return r;
                        }
                }

                if (!prohibit_ipc &&
                    IN_SET(log_target, LOG_TARGET_SYSLOG_OR_KMSG,
                                       LOG_TARGET_SYSLOG)) {
                        r = log_open_syslog();
                        if (r >= 0) {
                                log_close_journal();
                                log_close_console();
                                return r;
                        }
                }

                if (IN_SET(log_target, LOG_TARGET_AUTO,
                                       LOG_TARGET_JOURNAL_OR_KMSG,
                                       LOG_TARGET_SYSLOG_OR_KMSG,
                                       LOG_TARGET_KMSG)) {
                        r = log_open_kmsg();
                        if (r >= 0) {
                                log_close_journal();
                                log_close_syslog();
                                log_close_console();
                                return r;
                        }
                }
        }

        log_close_journal();
        log_close_syslog();

        return log_open_console();
}

void log_set_target(LogTarget target) {
        assert(target >= 0);
        assert(target < _LOG_TARGET_MAX);

        if (upgrade_syslog_to_journal) {
                if (target == LOG_TARGET_SYSLOG)
                        target = LOG_TARGET_JOURNAL;
                else if (target == LOG_TARGET_SYSLOG_OR_KMSG)
                        target = LOG_TARGET_JOURNAL_OR_KMSG;
        }

        log_target = target;
}

void log_close(void) {
        /* Do not call from library code. */

        log_close_journal();
        log_close_syslog();
        log_close_kmsg();
        log_close_console();
}

void log_forget_fds(void) {
        /* Do not call from library code. */

        console_fd = kmsg_fd = syslog_fd = journal_fd = -1;
}

void log_set_max_level_realm(LogRealm realm, int level) {
        assert((level & LOG_PRIMASK) == level);
        assert(realm < ELEMENTSOF(log_max_level));

        log_max_level[realm] = level;
}

void log_set_facility(int facility) {
        log_facility = facility;
}

static int write_to_console(
                int level,
                int error,
                const char *file,
                int line,
                const char *func,
                const char *buffer) {

        char location[256], prefix[1 + DECIMAL_STR_MAX(int) + 2];
        struct iovec iovec[6] = {};
        bool highlight;
        size_t n = 0;

        if (console_fd < 0)
                return 0;

        if (log_target == LOG_TARGET_CONSOLE_PREFIXED) {
                xsprintf(prefix, "<%i>", level);
                iovec[n++] = IOVEC_MAKE_STRING(prefix);
        }

        highlight = LOG_PRI(level) <= LOG_ERR && show_color;

        if (show_location) {
                (void) snprintf(location, sizeof location, "(%s:%i) ", file, line);
                iovec[n++] = IOVEC_MAKE_STRING(location);
        }

        if (highlight)
                iovec[n++] = IOVEC_MAKE_STRING(ANSI_HIGHLIGHT_RED);
        iovec[n++] = IOVEC_MAKE_STRING(buffer);
        if (highlight)
                iovec[n++] = IOVEC_MAKE_STRING(ANSI_NORMAL);
        iovec[n++] = IOVEC_MAKE_STRING("\n");

        if (writev(console_fd, iovec, n) < 0) {

                if (errno == EIO && getpid_cached() == 1) {

                        /* If somebody tried to kick us from our
                         * console tty (via vhangup() or suchlike),
                         * try to reconnect */

                        log_close_console();
                        log_open_console();

                        if (console_fd < 0)
                                return 0;

                        if (writev(console_fd, iovec, n) < 0)
                                return -errno;
                } else
                        return -errno;
        }

        return 1;
}

static int write_to_syslog(
                int level,
                int error,
                const char *file,
                int line,
                const char *func,
                const char *buffer) {

        char header_priority[2 + DECIMAL_STR_MAX(int) + 1],
             header_time[64],
             header_pid[4 + DECIMAL_STR_MAX(pid_t) + 1];
        struct iovec iovec[5] = {};
        struct msghdr msghdr = {
                .msg_iov = iovec,
                .msg_iovlen = ELEMENTSOF(iovec),
        };
        time_t t;
        struct tm tm;

        if (syslog_fd < 0)
                return 0;

        xsprintf(header_priority, "<%i>", level);

        t = (time_t) (now(CLOCK_REALTIME) / USEC_PER_SEC);
        if (!localtime_r(&t, &tm))
                return -EINVAL;

        if (strftime(header_time, sizeof(header_time), "%h %e %T ", &tm) <= 0)
                return -EINVAL;

        xsprintf(header_pid, "["PID_FMT"]: ", getpid_cached());

        iovec[0] = IOVEC_MAKE_STRING(header_priority);
        iovec[1] = IOVEC_MAKE_STRING(header_time);
        iovec[2] = IOVEC_MAKE_STRING(program_invocation_short_name);
        iovec[3] = IOVEC_MAKE_STRING(header_pid);
        iovec[4] = IOVEC_MAKE_STRING(buffer);

        /* When using syslog via SOCK_STREAM separate the messages by NUL chars */
        if (syslog_is_stream)
                iovec[4].iov_len++;

        for (;;) {
                ssize_t n;

                n = sendmsg(syslog_fd, &msghdr, MSG_NOSIGNAL);
                if (n < 0)
                        return -errno;

                if (!syslog_is_stream ||
                    (size_t) n >= IOVEC_TOTAL_SIZE(iovec, ELEMENTSOF(iovec)))
                        break;

                IOVEC_INCREMENT(iovec, ELEMENTSOF(iovec), n);
        }

        return 1;
}

static int write_to_kmsg(
                int level,
                int error,
                const char *file,
                int line,
                const char *func,
                const char *buffer) {

        char header_priority[2 + DECIMAL_STR_MAX(int) + 1],
             header_pid[4 + DECIMAL_STR_MAX(pid_t) + 1];
        struct iovec iovec[5] = {};

        if (kmsg_fd < 0)
                return 0;

        xsprintf(header_priority, "<%i>", level);
        xsprintf(header_pid, "["PID_FMT"]: ", getpid_cached());

        iovec[0] = IOVEC_MAKE_STRING(header_priority);
        iovec[1] = IOVEC_MAKE_STRING(program_invocation_short_name);
        iovec[2] = IOVEC_MAKE_STRING(header_pid);
        iovec[3] = IOVEC_MAKE_STRING(buffer);
        iovec[4] = IOVEC_MAKE_STRING("\n");

        if (writev(kmsg_fd, iovec, ELEMENTSOF(iovec)) < 0)
                return -errno;

        return 1;
}

static int log_do_header(
                char *header,
                size_t size,
                int level,
                int error,
                const char *file, int line, const char *func,
                const char *object_field, const char *object,
                const char *extra_field, const char *extra) {
        int r;

        error = IS_SYNTHETIC_ERRNO(error) ? 0 : ERRNO_VALUE(error);

        r = snprintf(header, size,
                     "PRIORITY=%i\n"
                     "SYSLOG_FACILITY=%i\n"
                     "%s%.256s%s"        /* CODE_FILE */
                     "%s%.*i%s"          /* CODE_LINE */
                     "%s%.256s%s"        /* CODE_FUNC */
                     "%s%.*i%s"          /* ERRNO */
                     "%s%.256s%s"        /* object */
                     "%s%.256s%s"        /* extra */
                     "SYSLOG_IDENTIFIER=%.256s\n",
                     LOG_PRI(level),
                     LOG_FAC(level),
                     isempty(file) ? "" : "CODE_FILE=",
                     isempty(file) ? "" : file,
                     isempty(file) ? "" : "\n",
                     line ? "CODE_LINE=" : "",
                     line ? 1 : 0, line, /* %.0d means no output too, special case for 0 */
                     line ? "\n" : "",
                     isempty(func) ? "" : "CODE_FUNC=",
                     isempty(func) ? "" : func,
                     isempty(func) ? "" : "\n",
                     error ? "ERRNO=" : "",
                     error ? 1 : 0, error,
                     error ? "\n" : "",
                     isempty(object) ? "" : object_field,
                     isempty(object) ? "" : object,
                     isempty(object) ? "" : "\n",
                     isempty(extra) ? "" : extra_field,
                     isempty(extra) ? "" : extra,
                     isempty(extra) ? "" : "\n",
                     program_invocation_short_name);
        assert_raw((size_t) r < size);

        return 0;
}

static int write_to_journal(
                int level,
                int error,
                const char *file,
                int line,
                const char *func,
                const char *object_field,
                const char *object,
                const char *extra_field,
                const char *extra,
                const char *buffer) {

        char header[LINE_MAX];
        struct iovec iovec[4] = {};
        struct msghdr mh = {};

        if (journal_fd < 0)
                return 0;

        log_do_header(header, sizeof(header), level, error, file, line, func, object_field, object, extra_field, extra);

        iovec[0] = IOVEC_MAKE_STRING(header);
        iovec[1] = IOVEC_MAKE_STRING("MESSAGE=");
        iovec[2] = IOVEC_MAKE_STRING(buffer);
        iovec[3] = IOVEC_MAKE_STRING("\n");

        mh.msg_iov = iovec;
        mh.msg_iovlen = ELEMENTSOF(iovec);

        if (sendmsg(journal_fd, &mh, MSG_NOSIGNAL) < 0)
                return -errno;

        return 1;
}

int log_dispatch_internal(
                int level,
                int error,
                const char *file,
                int line,
                const char *func,
                const char *object_field,
                const char *object,
                const char *extra_field,
                const char *extra,
                char *buffer) {

        assert_raw(buffer);

        if (log_target == LOG_TARGET_NULL)
                return -ERRNO_VALUE(error);

        /* Patch in LOG_DAEMON facility if necessary */
        if ((level & LOG_FACMASK) == 0)
                level |= log_facility;

        if (open_when_needed)
                log_open();

        do {
                char *e;
                int k = 0;

                buffer += strspn(buffer, NEWLINE);

                if (buffer[0] == 0)
                        break;

                if ((e = strpbrk(buffer, NEWLINE)))
                        *(e++) = 0;

                if (IN_SET(log_target, LOG_TARGET_AUTO,
                                       LOG_TARGET_JOURNAL_OR_KMSG,
                                       LOG_TARGET_JOURNAL)) {

                        k = write_to_journal(level, error, file, line, func, object_field, object, extra_field, extra, buffer);
                        if (k < 0 && k != -EAGAIN)
                                log_close_journal();
                }

                if (IN_SET(log_target, LOG_TARGET_SYSLOG_OR_KMSG,
                                       LOG_TARGET_SYSLOG)) {

                        k = write_to_syslog(level, error, file, line, func, buffer);
                        if (k < 0 && k != -EAGAIN)
                                log_close_syslog();
                }

                if (k <= 0 &&
                    IN_SET(log_target, LOG_TARGET_AUTO,
                                       LOG_TARGET_SYSLOG_OR_KMSG,
                                       LOG_TARGET_JOURNAL_OR_KMSG,
                                       LOG_TARGET_KMSG)) {

                        if (k < 0)
                                log_open_kmsg();

                        k = write_to_kmsg(level, error, file, line, func, buffer);
                        if (k < 0) {
                                log_close_kmsg();
                                log_open_console();
                        }
                }

                if (k <= 0)
                        (void) write_to_console(level, error, file, line, func, buffer);

                buffer = e;
        } while (buffer);

        if (open_when_needed)
                log_close();

        return -ERRNO_VALUE(error);
}

int log_dump_internal(
                int level,
                int error,
                const char *file,
                int line,
                const char *func,
                char *buffer) {

        LogRealm realm = LOG_REALM_REMOVE_LEVEL(level);
        PROTECT_ERRNO;

        /* This modifies the buffer... */

        if (_likely_(LOG_PRI(level) > log_max_level[realm]))
                return -ERRNO_VALUE(error);

        return log_dispatch_internal(level, error, file, line, func, NULL, NULL, NULL, NULL, buffer);
}

int log_internalv_realm(
                int level,
                int error,
                const char *file,
                int line,
                const char *func,
                const char *format,
                va_list ap) {

        LogRealm realm = LOG_REALM_REMOVE_LEVEL(level);
        char buffer[LINE_MAX];
        PROTECT_ERRNO;

        if (_likely_(LOG_PRI(level) > log_max_level[realm]))
                return -ERRNO_VALUE(error);

        /* Make sure that %m maps to the specified error (or "Success"). */
        errno = ERRNO_VALUE(error);

        (void) vsnprintf(buffer, sizeof buffer, format, ap);

        return log_dispatch_internal(level, error, file, line, func, NULL, NULL, NULL, NULL, buffer);
}

int log_internal_realm(
                int level,
                int error,
                const char *file,
                int line,
                const char *func,
                const char *format, ...) {

        va_list ap;
        int r;

        va_start(ap, format);
        r = log_internalv_realm(level, error, file, line, func, format, ap);
        va_end(ap);

        return r;
}

_printf_(10,0)
static int log_object_internalv(
                int level,
                int error,
                const char *file,
                int line,
                const char *func,
                const char *object_field,
                const char *object,
                const char *extra_field,
                const char *extra,
                const char *format,
                va_list ap) {

        PROTECT_ERRNO;
        char *buffer, *b;

        if (_likely_(LOG_PRI(level) > log_max_level[LOG_REALM_SYSTEMD]))
                return -ERRNO_VALUE(error);

        /* Make sure that %m maps to the specified error (or "Success"). */
        errno = ERRNO_VALUE(error);

        /* Prepend the object name before the message */
        if (object) {
                size_t n;

                n = strlen(object);
                buffer = newa(char, n + 2 + LINE_MAX);
                b = stpcpy(stpcpy(buffer, object), ": ");
        } else
                b = buffer = newa(char, LINE_MAX);

        (void) vsnprintf(b, LINE_MAX, format, ap);

        return log_dispatch_internal(level, error, file, line, func,
                                     object_field, object, extra_field, extra, buffer);
}

int log_object_internal(
                int level,
                int error,
                const char *file,
                int line,
                const char *func,
                const char *object_field,
                const char *object,
                const char *extra_field,
                const char *extra,
                const char *format, ...) {

        va_list ap;
        int r;

        va_start(ap, format);
        r = log_object_internalv(level, error, file, line, func, object_field, object, extra_field, extra, format, ap);
        va_end(ap);

        return r;
}

static void log_assert(
                int level,
                const char *text,
                const char *file,
                int line,
                const char *func,
                const char *format) {

        static char buffer[LINE_MAX];
        LogRealm realm = LOG_REALM_REMOVE_LEVEL(level);

        if (_likely_(LOG_PRI(level) > log_max_level[realm]))
                return;

        DISABLE_WARNING_FORMAT_NONLITERAL;
        (void) snprintf(buffer, sizeof buffer, format, text, file, line, func);
        REENABLE_WARNING;

        log_abort_msg = buffer;

        log_dispatch_internal(level, 0, file, line, func, NULL, NULL, NULL, NULL, buffer);
}

_noreturn_ void log_assert_failed_realm(
                LogRealm realm,
                const char *text,
                const char *file,
                int line,
                const char *func) {
        log_open();
        log_assert(LOG_REALM_PLUS_LEVEL(realm, LOG_CRIT), text, file, line, func,
                   "Assertion '%s' failed at %s:%u, function %s(). Aborting.");
        abort();
}

_noreturn_ void log_assert_failed_unreachable_realm(
                LogRealm realm,
                const char *text,
                const char *file,
                int line,
                const char *func) {
        log_open();
        log_assert(LOG_REALM_PLUS_LEVEL(realm, LOG_CRIT), text, file, line, func,
                   "Code should not be reached '%s' at %s:%u, function %s(). Aborting.");
        abort();
}

void log_assert_failed_return_realm(
                LogRealm realm,
                const char *text,
                const char *file,
                int line,
                const char *func) {
        PROTECT_ERRNO;
        log_assert(LOG_REALM_PLUS_LEVEL(realm, LOG_DEBUG), text, file, line, func,
                   "Assertion '%s' failed at %s:%u, function %s(). Ignoring.");
}

int log_oom_internal(LogRealm realm, const char *file, int line, const char *func) {
        return log_internal_realm(LOG_REALM_PLUS_LEVEL(realm, LOG_ERR),
                                  ENOMEM, file, line, func, "Out of memory.");
}

int log_format_iovec(
                struct iovec *iovec,
                size_t iovec_len,
                size_t *n,
                bool newline_separator,
                int error,
                const char *format,
                va_list ap) {

        static const char nl = '\n';

        while (format && *n + 1 < iovec_len) {
                va_list aq;
                char *m;
                int r;

                /* We need to copy the va_list structure,
                 * since vasprintf() leaves it afterwards at
                 * an undefined location */

                errno = ERRNO_VALUE(error);

                va_copy(aq, ap);
                r = vasprintf(&m, format, aq);
                va_end(aq);
                if (r < 0)
                        return -EINVAL;

                /* Now, jump enough ahead, so that we point to
                 * the next format string */
                VA_FORMAT_ADVANCE(format, ap);

                iovec[(*n)++] = IOVEC_MAKE_STRING(m);

                if (newline_separator) {
                        iovec[*n].iov_base = (char*) &nl;
                        iovec[*n].iov_len = 1;
                        (*n)++;
                }

                format = va_arg(ap, char *);
        }
        return 0;
}

int log_struct_internal(
                int level,
                int error,
                const char *file,
                int line,
                const char *func,
                const char *format, ...) {

        LogRealm realm = LOG_REALM_REMOVE_LEVEL(level);
        char buf[LINE_MAX];
        bool found = false;
        PROTECT_ERRNO;
        va_list ap;

        if (_likely_(LOG_PRI(level) > log_max_level[realm]) ||
            log_target == LOG_TARGET_NULL)
                return -ERRNO_VALUE(error);

        if ((level & LOG_FACMASK) == 0)
                level |= log_facility;

        if (IN_SET(log_target,
                   LOG_TARGET_AUTO,
                   LOG_TARGET_JOURNAL_OR_KMSG,
                   LOG_TARGET_JOURNAL)) {

                if (open_when_needed)
                        log_open_journal();

                if (journal_fd >= 0) {
                        char header[LINE_MAX];
                        struct iovec iovec[17] = {};
                        size_t n = 0, i;
                        int r;
                        struct msghdr mh = {
                                .msg_iov = iovec,
                        };
                        bool fallback = false;

                        /* If the journal is available do structured logging.
                         * Do not report the errno if it is synthetic. */
                        log_do_header(header, sizeof(header), level, error, file, line, func, NULL, NULL, NULL, NULL);
                        iovec[n++] = IOVEC_MAKE_STRING(header);

                        va_start(ap, format);
                        r = log_format_iovec(iovec, ELEMENTSOF(iovec), &n, true, error, format, ap);
                        if (r < 0)
                                fallback = true;
                        else {
                                mh.msg_iovlen = n;
                                (void) sendmsg(journal_fd, &mh, MSG_NOSIGNAL);
                        }

                        va_end(ap);
                        for (i = 1; i < n; i += 2)
                                free(iovec[i].iov_base);

                        if (!fallback) {
                                if (open_when_needed)
                                        log_close();

                                return -ERRNO_VALUE(error);
                        }
                }
        }

        /* Fallback if journal logging is not available or didn't work. */

        va_start(ap, format);
        while (format) {
                va_list aq;

                errno = ERRNO_VALUE(error);

                va_copy(aq, ap);
                (void) vsnprintf(buf, sizeof buf, format, aq);
                va_end(aq);

                if (startswith(buf, "MESSAGE=")) {
                        found = true;
                        break;
                }

                VA_FORMAT_ADVANCE(format, ap);

                format = va_arg(ap, char *);
        }
        va_end(ap);

        if (!found) {
                if (open_when_needed)
                        log_close();

                return -ERRNO_VALUE(error);
        }

        return log_dispatch_internal(level, error, file, line, func, NULL, NULL, NULL, NULL, buf + 8);
}

int log_struct_iovec_internal(
                int level,
                int error,
                const char *file,
                int line,
                const char *func,
                const struct iovec input_iovec[],
                size_t n_input_iovec) {

        LogRealm realm = LOG_REALM_REMOVE_LEVEL(level);
        PROTECT_ERRNO;
        size_t i;
        char *m;

        if (_likely_(LOG_PRI(level) > log_max_level[realm]) ||
            log_target == LOG_TARGET_NULL)
                return -ERRNO_VALUE(error);

        if ((level & LOG_FACMASK) == 0)
                level |= log_facility;

        if (IN_SET(log_target, LOG_TARGET_AUTO,
                               LOG_TARGET_JOURNAL_OR_KMSG,
                               LOG_TARGET_JOURNAL) &&
            journal_fd >= 0) {

                struct iovec iovec[1 + n_input_iovec*2];
                char header[LINE_MAX];
                struct msghdr mh = {
                        .msg_iov = iovec,
                        .msg_iovlen = 1 + n_input_iovec*2,
                };

                log_do_header(header, sizeof(header), level, error, file, line, func, NULL, NULL, NULL, NULL);
                iovec[0] = IOVEC_MAKE_STRING(header);

                for (i = 0; i < n_input_iovec; i++) {
                        iovec[1+i*2] = input_iovec[i];
                        iovec[1+i*2+1] = IOVEC_MAKE_STRING("\n");
                }

                if (sendmsg(journal_fd, &mh, MSG_NOSIGNAL) >= 0)
                        return -ERRNO_VALUE(error);
        }

        for (i = 0; i < n_input_iovec; i++)
                if (memory_startswith(input_iovec[i].iov_base, input_iovec[i].iov_len, "MESSAGE="))
                        break;

        if (_unlikely_(i >= n_input_iovec)) /* Couldn't find MESSAGE=? */
                return -ERRNO_VALUE(error);

        m = strndupa(input_iovec[i].iov_base + STRLEN("MESSAGE="),
                     input_iovec[i].iov_len - STRLEN("MESSAGE="));

        return log_dispatch_internal(level, error, file, line, func, NULL, NULL, NULL, NULL, m);
}

int log_set_target_from_string(const char *e) {
        LogTarget t;

        t = log_target_from_string(e);
        if (t < 0)
                return -EINVAL;

        log_set_target(t);
        return 0;
}

int log_set_max_level_from_string_realm(LogRealm realm, const char *e) {
        int t;

        t = log_level_from_string(e);
        if (t < 0)
                return -EINVAL;

        log_set_max_level_realm(realm, t);
        return 0;
}

static int parse_proc_cmdline_item(const char *key, const char *value, void *data) {

        /*
         * The systemd.log_xyz= settings are parsed by all tools, and
         * so is "debug".
         *
         * However, "quiet" is only parsed by PID 1, and only turns of
         * status output to /dev/console, but does not alter the log
         * level.
         */

        if (streq(key, "debug") && !value)
                log_set_max_level(LOG_DEBUG);

        else if (proc_cmdline_key_streq(key, "systemd.log_target")) {

                if (proc_cmdline_value_missing(key, value))
                        return 0;

                if (log_set_target_from_string(value) < 0)
                        log_warning("Failed to parse log target '%s'. Ignoring.", value);

        } else if (proc_cmdline_key_streq(key, "systemd.log_level")) {

                if (proc_cmdline_value_missing(key, value))
                        return 0;

                if (log_set_max_level_from_string(value) < 0)
                        log_warning("Failed to parse log level '%s'. Ignoring.", value);

        } else if (proc_cmdline_key_streq(key, "systemd.log_color")) {

                if (log_show_color_from_string(value ?: "1") < 0)
                        log_warning("Failed to parse log color setting '%s'. Ignoring.", value);

        } else if (proc_cmdline_key_streq(key, "systemd.log_location")) {

                if (log_show_location_from_string(value ?: "1") < 0)
                        log_warning("Failed to parse log location setting '%s'. Ignoring.", value);
        }

        return 0;
}

void log_parse_environment_realm(LogRealm realm) {
        /* Do not call from library code. */

        const char *e;

        if (get_ctty_devnr(0, NULL) < 0)
                /* Only try to read the command line in daemons.  We assume that anything that has a controlling tty is
                   user stuff. */
                (void) proc_cmdline_parse(parse_proc_cmdline_item, NULL, PROC_CMDLINE_STRIP_RD_PREFIX);

        e = getenv("SYSTEMD_LOG_TARGET");
        if (e && log_set_target_from_string(e) < 0)
                log_warning("Failed to parse log target '%s'. Ignoring.", e);

        e = getenv("SYSTEMD_LOG_LEVEL");
        if (e && log_set_max_level_from_string_realm(realm, e) < 0)
                log_warning("Failed to parse log level '%s'. Ignoring.", e);

        e = getenv("SYSTEMD_LOG_COLOR");
        if (e && log_show_color_from_string(e) < 0)
                log_warning("Failed to parse bool '%s'. Ignoring.", e);

        e = getenv("SYSTEMD_LOG_LOCATION");
        if (e && log_show_location_from_string(e) < 0)
                log_warning("Failed to parse bool '%s'. Ignoring.", e);
}

LogTarget log_get_target(void) {
        return log_target;
}

int log_get_max_level_realm(LogRealm realm) {
        return log_max_level[realm];
}

void log_show_color(bool b) {
        show_color = b;
}

bool log_get_show_color(void) {
        return show_color;
}

void log_show_location(bool b) {
        show_location = b;
}

bool log_get_show_location(void) {
        return show_location;
}

int log_show_color_from_string(const char *e) {
        int t;

        t = parse_boolean(e);
        if (t < 0)
                return t;

        log_show_color(t);
        return 0;
}

int log_show_location_from_string(const char *e) {
        int t;

        t = parse_boolean(e);
        if (t < 0)
                return t;

        log_show_location(t);
        return 0;
}

bool log_on_console(void) {
        if (IN_SET(log_target, LOG_TARGET_CONSOLE,
                               LOG_TARGET_CONSOLE_PREFIXED))
                return true;

        return syslog_fd < 0 && kmsg_fd < 0 && journal_fd < 0;
}

static const char *const log_target_table[_LOG_TARGET_MAX] = {
        [LOG_TARGET_CONSOLE] = "console",
        [LOG_TARGET_CONSOLE_PREFIXED] = "console-prefixed",
        [LOG_TARGET_KMSG] = "kmsg",
        [LOG_TARGET_JOURNAL] = "journal",
        [LOG_TARGET_JOURNAL_OR_KMSG] = "journal-or-kmsg",
        [LOG_TARGET_SYSLOG] = "syslog",
        [LOG_TARGET_SYSLOG_OR_KMSG] = "syslog-or-kmsg",
        [LOG_TARGET_AUTO] = "auto",
        [LOG_TARGET_NULL] = "null",
};

DEFINE_STRING_TABLE_LOOKUP(log_target, LogTarget);

void log_received_signal(int level, const struct signalfd_siginfo *si) {
        assert(si);

        if (pid_is_valid(si->ssi_pid)) {
                _cleanup_free_ char *p = NULL;

                (void) get_process_comm(si->ssi_pid, &p);

                log_full(level,
                         "Received SIG%s from PID %"PRIu32" (%s).",
                         signal_to_string(si->ssi_signo),
                         si->ssi_pid, strna(p));
        } else
                log_full(level,
                         "Received SIG%s.",
                         signal_to_string(si->ssi_signo));
}

int log_syntax_internal(
                const char *unit,
                int level,
                const char *config_file,
                unsigned config_line,
                int error,
                const char *file,
                int line,
                const char *func,
                const char *format, ...) {

        PROTECT_ERRNO;
        char buffer[LINE_MAX];
        va_list ap;
        const char *unit_fmt = NULL;

        if (_likely_(LOG_PRI(level) > log_max_level[LOG_REALM_SYSTEMD]) ||
            log_target == LOG_TARGET_NULL)
                return -ERRNO_VALUE(error);

        errno = error;

        va_start(ap, format);
        (void) vsnprintf(buffer, sizeof buffer, format, ap);
        va_end(ap);

        if (unit)
                unit_fmt = getpid_cached() == 1 ? "UNIT=%s" : "USER_UNIT=%s";

        return log_struct_internal(
                        LOG_REALM_PLUS_LEVEL(LOG_REALM_SYSTEMD, level),
                        error,
                        file, line, func,
                        "MESSAGE_ID=" SD_MESSAGE_INVALID_CONFIGURATION_STR,
                        "CONFIG_FILE=%s", config_file,
                        "CONFIG_LINE=%u", config_line,
                        LOG_MESSAGE("%s:%u: %s", config_file, config_line, buffer),
                        unit_fmt, unit,
                        NULL);
}

int log_syntax_invalid_utf8_internal(
                const char *unit,
                int level,
                const char *config_file,
                unsigned config_line,
                const char *file,
                int line,
                const char *func,
                const char *rvalue) {

        _cleanup_free_ char *p = NULL;

        if (rvalue)
                p = utf8_escape_invalid(rvalue);

        log_syntax_internal(unit, level, config_file, config_line, 0, file, line, func,
                            "String is not UTF-8 clean, ignoring assignment: %s", strna(p));

        return -EINVAL;
}

void log_set_upgrade_syslog_to_journal(bool b) {
        upgrade_syslog_to_journal = b;

        /* Make the change effective immediately */
        if (b) {
                if (log_target == LOG_TARGET_SYSLOG)
                        log_target = LOG_TARGET_JOURNAL;
                else if (log_target == LOG_TARGET_SYSLOG_OR_KMSG)
                        log_target = LOG_TARGET_JOURNAL_OR_KMSG;
        }
}

void log_set_always_reopen_console(bool b) {
        always_reopen_console = b;
}

void log_set_open_when_needed(bool b) {
        open_when_needed = b;
}

void log_set_prohibit_ipc(bool b) {
        prohibit_ipc = b;
}

int log_emergency_level(void) {
        /* Returns the log level to use for log_emergency() logging. We use LOG_EMERG only when we are PID 1, as only
         * then the system of the whole system is obviously affected. */

        return getpid_cached() == 1 ? LOG_EMERG : LOG_ERR;
}

int log_dup_console(void) {
        int copy;

        /* Duplicate the fd we use for fd logging if it's < 3 and use the copy from now on. This call is useful
         * whenever we want to continue logging through the original fd, but want to rearrange stderr. */

        if (console_fd >= 3)
                return 0;

        copy = fcntl(console_fd, F_DUPFD_CLOEXEC, 3);
        if (copy < 0)
                return -errno;

        console_fd = copy;
        return 0;
}

void log_setup_service(void) {
        /* Sets up logging the way it is most appropriate for running a program as a service. Note that using this
         * doesn't make the binary unsuitable for invocation on the command line, as log output will still go to the
         * terminal if invoked interactively. */

        log_set_target(LOG_TARGET_AUTO);
        log_parse_environment();
        log_open();
}