*: Convert thread_cancelXXX to event_cancelXXX

[mirror_frr.git] / lib / zlog_5424.c

// SPDX-License-Identifier: ISC
/*
 * Copyright (c) 2015-21  David Lamparter, for NetDEF, Inc.
 */

/* when you work on this code, please install a fuzzer (e.g. AFL) and run
 * tests/lib/fuzz_zlog.c
 *
 * The most likely type of bug in this code is an off-by-one error in the
 * buffer management pieces, and this isn't easily covered by an unit test
 * or topotests.  Fuzzing is the best tool here, but the CI can't do that
 * since it's quite resource intensive.
 */

#include "zebra.h"

#include "zlog_5424.h"

#include <sys/un.h>
#include <syslog.h>

#include "memory.h"
#include "frrcu.h"
#include "printfrr.h"
#include "typerb.h"
#include "frr_pthread.h"
#include "command.h"
#include "monotime.h"
#include "event.h"

#include "lib/version.h"
#include "lib/lib_errors.h"

DEFINE_MTYPE_STATIC(LOG, LOG_5424, "extended log target");
DEFINE_MTYPE_STATIC(LOG, LOG_5424_ROTATE, "extended log rotate helper");

/* the actual log target data structure
 *
 * remember this is RCU'd by the core zlog functions.  Changing anything
 * works by allocating a new struct, filling it, adding it, and removing the
 * old one.
 */
struct zlt_5424 {
        struct zlog_target zt;

        atomic_uint_fast32_t fd;

        enum zlog_5424_format fmt;
        uint32_t ts_flags;
        int facility;

        /* the various extra pieces to add... */
        bool kw_version : 1;
        bool kw_location : 1;
        bool kw_uid : 1;
        bool kw_ec : 1;
        bool kw_args : 1;

        /* some formats may or may not include the trailing \n */
        bool use_nl : 1;

        /* for DGRAM & SEQPACKET sockets, send 1 log message per packet, since
         * the socket preserves packet boundaries.  On Linux, this uses
         * sendmmsg() for efficiency, on other systems we need a syscall each.
         */
        bool packets : 1;

        /* for DGRAM, in order to not have to reconnect, we need to use
         * sendto()/sendmsg() with the destination given; otherwise we'll get
         * ENOTCONN.  (We do a connect(), which serves to verify the type of
         * socket, but if the receiver goes away, the kernel disconnects the
         * socket so writev() no longer works since the destination is now
         * unspecified.)
         */
        struct sockaddr_storage sa;
        socklen_t sa_len;

        /* these are both getting set, but current_err is cleared on success,
         * so we know whether the error is current or past.
         */
        int last_err, current_err;
        atomic_size_t lost_msgs;
        struct timeval last_err_ts;

        struct rcu_head_close head_close;
};

static int zlog_5424_open(struct zlog_cfg_5424 *zcf, int sock_type);

/* rough header length estimate
 * ============================
 *
 *   ^ = might grow
 *
 *  49^ longest filename (pceplib/test/pcep_utils_double_linked_list_test.h)
 *   5^ highest line number (48530, bgpd/bgp_nb_config.c)
 *  65^ longest function name
 *      (lib_prefix_list_entry_ipv6_prefix_length_greater_or_equal_destroy)
 *  11  unique id ("XXXXX-XXXXX")
 *  10  EC ("4294967295" or "0xffffffff")
 *  35  ISO8601 TS at full length ("YYYY-MM-DD HH:MM:SS.NNNNNNNNN+ZZ:ZZ")
 * ---
 * 175
 *
 * rarely used (hopefully...):
 *  26^ FRR_VERSION ("10.10.10-dev-gffffffffffff")
 * ---
 * 201
 *
 * x16  highest number of format parameters currently
 *  40  estimate for hostname + 2*daemon + pid
 *
 * specific format overhead:
 *
 * RFC3164 - shorter than the others
 * RFC5424 - 175 + "<999>1 "=7 + 52 (location@50145) + 40 (host/...)
 *      rarely: + 65 + 26 (for [origin])
 *      args:  16 * (8 + per-arg (20?)) = ~448
 *
 * so without "args@", origin or (future) keywords, around 256 seems OK
 * with args@ and/or origin and/or keywords, 512 seems more reasonable
 *
 * but - note the code allocates this amount multiplied by the number of
 * messages in the incoming batch (minimum 3), this means short messages and
 * long messages smooth each other out.
 *
 * Since the code handles space-exceeded by grabbing a bunch of stack memory,
 * a reasonable middle ground estimate is desirable here, so ...
 * *drumroll*
 * let's go with 128 + args?128.  (remember the minimum 3 multiplier)
 *
 * low_space is the point where we don't try to fit another message in & just
 * submit what we have to the kernel.
 *
 * The zlog code only buffers debug & informational messages, so in production
 * usage most of the calls will be writing out only 1 message.  This makes
 * the min *3 multiplier quite useful.
 */

static inline size_t zlog_5424_bufsz(struct zlt_5424 *zte, size_t nmsgs,
                                     size_t *low_space)
{
        size_t ret = 128;

        if (zte->kw_args)
                ret += 128;
        *low_space = ret;
        return ret * MAX(nmsgs, 3);
}

struct state {
        struct fbuf *fbuf;
        struct iovec *iov;
};

/* stack-based keyword support is likely to bump this to 3 or 4 */
#define IOV_PER_MSG 2
_Static_assert(IOV_MAX >= IOV_PER_MSG,
               "this code won't work with IOV_MAX < IOV_PER_MSG");

/* the following functions are quite similar, but trying to merge them just
 * makes a big mess.  check the others when touching one.
 *
 *              timestamp       keywords        hostname
 * RFC5424      ISO8601         yes             yes
 * RFC3164      RFC3164         no              yes
 * local        RFC3164         no              no
 * journald     ISO8601(unused) yes             (unused)
 */

static size_t zlog_5424_one(struct zlt_5424 *zte, struct zlog_msg *msg,
                            struct state *state)
{
        size_t textlen;
        struct fbuf *fbuf = state->fbuf;
        char *orig_pos = fbuf->pos;
        size_t need = 0;
        int prio = zlog_msg_prio(msg);
        intmax_t pid, tid;

        zlog_msg_pid(msg, &pid, &tid);

        need += bprintfrr(fbuf, "<%d>1 ", prio | zte->facility);
        need += zlog_msg_ts(msg, fbuf, zte->ts_flags);
        need += bprintfrr(fbuf, " %s %s %jd %.*s ", cmd_hostname_get() ?: "-",
                          zlog_progname, pid, (int)(zlog_prefixsz - 2),
                          zlog_prefix);

        if (zte->kw_version)
                need += bprintfrr(
                        fbuf,
                        "[origin enterpriseId=\"50145\" software=\"FRRouting\" swVersion=\"%s\"]",
                        FRR_VERSION);

        const struct xref_logmsg *xref;
        struct xrefdata *xrefdata;

        need += bprintfrr(fbuf, "[location@50145 tid=\"%jd\"", tid);
        if (zlog_instance > 0)
                need += bprintfrr(fbuf, " instance=\"%d\"", zlog_instance);

        xref = zlog_msg_xref(msg);
        xrefdata = xref ? xref->xref.xrefdata : NULL;
        if (xrefdata) {
                if (zte->kw_uid)
                        need += bprintfrr(fbuf, " id=\"%s\"", xrefdata->uid);
                if (zte->kw_ec && prio <= LOG_WARNING)
                        need += bprintfrr(fbuf, " ec=\"%u\"", xref->ec);
                if (zte->kw_location)
                        need += bprintfrr(
                                fbuf, " file=\"%s\" line=\"%d\" func=\"%s\"",
                                xref->xref.file, xref->xref.line,
                                xref->xref.func);
        }
        need += bputch(fbuf, ']');

        size_t hdrlen, n_argpos;
        const struct fmt_outpos *argpos;
        const char *text;

        text = zlog_msg_text(msg, &textlen);
        zlog_msg_args(msg, &hdrlen, &n_argpos, &argpos);

        if (zte->kw_args && n_argpos) {
                need += bputs(fbuf, "[args@50145");

                for (size_t i = 0; i < n_argpos; i++) {
                        int len = argpos[i].off_end - argpos[i].off_start;

                        need += bprintfrr(fbuf, " arg%zu=%*pSQsq", i + 1, len,
                                          text + argpos[i].off_start);
                }

                need += bputch(fbuf, ']');
        }

        need += bputch(fbuf, ' ');

        if (orig_pos + need > fbuf->buf + fbuf->len) {
                /* not enough space in the buffer for headers.  the loop in
                 * zlog_5424() will flush other messages that are already in
                 * the buffer, grab a bigger buffer if needed, and try again.
                 */
                fbuf->pos = orig_pos;
                return need;
        }

        /* NB: zlog_5424 below assumes we use max. IOV_PER_MSG iovs here */
        state->iov->iov_base = orig_pos;
        state->iov->iov_len = fbuf->pos - orig_pos;
        state->iov++;

        state->iov->iov_base = (char *)text + hdrlen;
        state->iov->iov_len = textlen - hdrlen + zte->use_nl;
        state->iov++;
        return 0;
}

static size_t zlog_3164_one(struct zlt_5424 *zte, struct zlog_msg *msg,
                            struct state *state)
{
        size_t textlen;
        struct fbuf *fbuf = state->fbuf;
        char *orig_pos = fbuf->pos;
        size_t need = 0;
        int prio = zlog_msg_prio(msg);
        intmax_t pid, tid;

        zlog_msg_pid(msg, &pid, &tid);

        need += bprintfrr(fbuf, "<%d>", prio | zte->facility);
        need += zlog_msg_ts_3164(msg, fbuf, zte->ts_flags);
        if (zte->fmt != ZLOG_FMT_LOCAL) {
                need += bputch(fbuf, ' ');
                need += bputs(fbuf, cmd_hostname_get() ?: "-");
        }
        need += bprintfrr(fbuf, " %s[%jd]: ", zlog_progname, pid);

        if (orig_pos + need > fbuf->buf + fbuf->len) {
                /* not enough space in the buffer for headers.  loop in
                 * zlog_5424() will flush other messages that are already in
                 * the buffer, grab a bigger buffer if needed, and try again.
                 */
                fbuf->pos = orig_pos;
                return need;
        }

        /* NB: zlog_5424 below assumes we use max. IOV_PER_MSG iovs here */
        state->iov->iov_base = orig_pos;
        state->iov->iov_len = fbuf->pos - orig_pos;
        state->iov++;

        state->iov->iov_base = (char *)zlog_msg_text(msg, &textlen);
        state->iov->iov_len = textlen + zte->use_nl;
        state->iov++;
        return 0;
}

static size_t zlog_journald_one(struct zlt_5424 *zte, struct zlog_msg *msg,
                                struct state *state)
{
        size_t textlen;
        struct fbuf *fbuf = state->fbuf;
        char *orig_pos = fbuf->pos;
        size_t need = 0;
        int prio = zlog_msg_prio(msg);
        intmax_t pid, tid;

        zlog_msg_pid(msg, &pid, &tid);

        need += bprintfrr(fbuf,
                          "PRIORITY=%d\n"
                          "SYSLOG_FACILITY=%d\n"
                          "TID=%jd\n"
                          "FRR_DAEMON=%s\n"
                          "SYSLOG_TIMESTAMP=",
                          prio, zte->facility, tid, zlog_progname);
        need += zlog_msg_ts(msg, fbuf, zte->ts_flags);
        need += bputch(fbuf, '\n');
        if (zlog_instance > 0)
                need += bprintfrr(fbuf, "FRR_INSTANCE=%d\n", zlog_instance);

        const struct xref_logmsg *xref;
        struct xrefdata *xrefdata;

        xref = zlog_msg_xref(msg);
        xrefdata = xref ? xref->xref.xrefdata : NULL;
        if (xrefdata) {
                if (zte->kw_uid && xrefdata->uid[0])
                        need += bprintfrr(fbuf, "FRR_ID=%s\n", xrefdata->uid);
                if (zte->kw_ec && prio <= LOG_WARNING)
                        need += bprintfrr(fbuf, "FRR_EC=%d\n", xref->ec);
                if (zte->kw_location)
                        need += bprintfrr(fbuf,
                                          "CODE_FILE=%s\n"
                                          "CODE_LINE=%d\n"
                                          "CODE_FUNC=%s\n",
                                          xref->xref.file, xref->xref.line,
                                          xref->xref.func);
        }

        size_t hdrlen, n_argpos;
        const struct fmt_outpos *argpos;
        const char *text;

        text = zlog_msg_text(msg, &textlen);
        zlog_msg_args(msg, &hdrlen, &n_argpos, &argpos);

        if (zte->kw_args && n_argpos) {
                for (size_t i = 0; i < n_argpos; i++) {
                        int len = argpos[i].off_end - argpos[i].off_start;

                        /* rather than escape the value, we could use
                         * journald's binary encoding, but that seems a bit
                         * excessive/unnecessary.  99% of things we print here
                         * will just output 1:1 with %pSE.
                         */
                        need += bprintfrr(fbuf, "FRR_ARG%zu=%*pSE\n", i + 1,
                                          len, text + argpos[i].off_start);
                }
        }

        need += bputs(fbuf, "MESSAGE=");

        if (orig_pos + need > fbuf->buf + fbuf->len) {
                /* not enough space in the buffer for headers.  loop in
                 * zlog_5424() will flush other messages that are already in
                 * the buffer, grab a bigger buffer if needed, and try again.
                 */
                fbuf->pos = orig_pos;
                return need;
        }

        /* NB: zlog_5424 below assumes we use max. IOV_PER_MSG iovs here */
        state->iov->iov_base = orig_pos;
        state->iov->iov_len = fbuf->pos - orig_pos;
        state->iov++;

        state->iov->iov_base = (char *)text + hdrlen;
        state->iov->iov_len = textlen - hdrlen + 1;
        state->iov++;
        return 0;
}

static size_t zlog_one(struct zlt_5424 *zte, struct zlog_msg *msg,
                       struct state *state)
{
        switch (zte->fmt) {
        case ZLOG_FMT_5424:
                return zlog_5424_one(zte, msg, state);
        case ZLOG_FMT_3164:
        case ZLOG_FMT_LOCAL:
                return zlog_3164_one(zte, msg, state);
        case ZLOG_FMT_JOURNALD:
                return zlog_journald_one(zte, msg, state);
        }
        return 0;
}

static void zlog_5424_err(struct zlt_5424 *zte, size_t count)
{
        if (!count) {
                zte->current_err = 0;
                return;
        }

        /* only the counter is atomic because otherwise it'd be meaningless */
        atomic_fetch_add_explicit(&zte->lost_msgs, count, memory_order_relaxed);

        /* these are non-atomic and can provide wrong results when read, but
         * since they're only for debugging / display, that's OK.
         */
        zte->current_err = zte->last_err = errno;
        monotime(&zte->last_err_ts);
}

static void zlog_5424(struct zlog_target *zt, struct zlog_msg *msgs[],
                      size_t nmsgs)
{
        size_t i;
        struct zlt_5424 *zte = container_of(zt, struct zlt_5424, zt);
        int fd, ret;
        size_t niov = MIN(IOV_PER_MSG * nmsgs, IOV_MAX);
        struct iovec iov[niov], *iov_last = iov + niov;
        struct mmsghdr mmsg[zte->packets ? nmsgs : 1], *mpos = mmsg;
        size_t count = 0;

        /* refer to size estimate at top of file */
        size_t low_space;
        char hdr_buf[zlog_5424_bufsz(zte, nmsgs, &low_space)];
        struct fbuf hdr_pos = {
                .buf = hdr_buf,
                .pos = hdr_buf,
                .len = sizeof(hdr_buf),
        };
        struct state state = {
                .fbuf = &hdr_pos,
                .iov = iov,
        };

        fd = atomic_load_explicit(&zte->fd, memory_order_relaxed);

        memset(mmsg, 0, sizeof(mmsg));
        if (zte->sa_len) {
                for (i = 0; i < array_size(mmsg); i++) {
                        mmsg[i].msg_hdr.msg_name = (struct sockaddr *)&zte->sa;
                        mmsg[i].msg_hdr.msg_namelen = zte->sa_len;
                }
        }
        mmsg[0].msg_hdr.msg_iov = iov;

        for (i = 0; i < nmsgs; i++) {
                int prio = zlog_msg_prio(msgs[i]);
                size_t need = 0;

                if (prio <= zte->zt.prio_min) {
                        if (zte->packets)
                                mpos->msg_hdr.msg_iov = state.iov;

                        need = zlog_one(zte, msgs[i], &state);

                        if (zte->packets) {
                                mpos->msg_hdr.msg_iovlen =
                                        state.iov - mpos->msg_hdr.msg_iov;
                                mpos++;
                        }
                        count++;
                }

                /* clang-format off */
                if ((need
                     || (size_t)(hdr_pos.buf + hdr_pos.len - hdr_pos.pos)
                                < low_space
                     || i + 1 == nmsgs
                     || state.iov + IOV_PER_MSG > iov_last)
                    && state.iov > iov) {
                        /* clang-format on */

                        if (zte->packets) {
                                struct mmsghdr *sendpos;

                                for (sendpos = mmsg; sendpos < mpos;) {
                                        ret = sendmmsg(fd, sendpos,
                                                       mpos - sendpos, 0);
                                        if (ret <= 0)
                                                break;
                                        sendpos += ret;
                                }
                                zlog_5424_err(zte, mpos - sendpos);
                                mpos = mmsg;
                        } else {
                                if (!zte->sa_len)
                                        ret = writev(fd, iov, state.iov - iov);
                                else {
                                        mpos->msg_hdr.msg_iovlen =
                                                state.iov - iov;
                                        ret = sendmsg(fd, &mpos->msg_hdr, 0);
                                }

                                if (ret < 0)
                                        zlog_5424_err(zte, count);
                                else
                                        zlog_5424_err(zte, 0);
                        }

                        count = 0;
                        hdr_pos.pos = hdr_buf;
                        state.iov = iov;
                }

                /* if need == 0, we just put a message (or nothing) in the
                 * buffer and are continuing for more to batch in a single
                 * writev()
                 */
                if (need == 0)
                        continue;

                if (need && need <= sizeof(hdr_buf)) {
                        /* don't need to allocate, just try this msg
                         * again without other msgs already using up
                         * buffer space
                         */
                        i--;
                        continue;
                }

                /* need > sizeof(hdr_buf), need to grab some memory.  Taking
                 * it off the stack is fine here.
                 */
                char buf2[need];
                struct fbuf fbuf2 = {
                        .buf = buf2,
                        .pos = buf2,
                        .len = sizeof(buf2),
                };

                state.fbuf = &fbuf2;
                need = zlog_one(zte, msgs[i], &state);
                assert(need == 0);

                if (!zte->sa_len)
                        ret = writev(fd, iov, state.iov - iov);
                else {
                        mpos->msg_hdr.msg_iovlen = state.iov - iov;
                        ret = sendmsg(fd, &mpos->msg_hdr, 0);
                }

                if (ret < 0)
                        zlog_5424_err(zte, 1);
                else
                        zlog_5424_err(zte, 0);

                count = 0;
                state.fbuf = &hdr_pos;
                state.iov = iov;
                mpos = mmsg;
        }

        assert(state.iov == iov);
}

/* strftime(), gmtime_r() and localtime_r() aren't AS-Safe (they access locale
 * data), but we need an AS-Safe timestamp below :(
 */
static void gmtime_assafe(time_t ts, struct tm *res)
{
        res->tm_sec = ts % 60;
        ts /= 60;
        res->tm_min = ts % 60;
        ts /= 60;
        res->tm_hour = ts % 24;
        ts /= 24;

        ts -= 11017; /* start on 2020-03-01, 11017 days since 1970-01-01 */

        /* 1461 days = 3 regular years + 1 leap year
         * this works until 2100, which isn't a leap year
         *
         * struct tm.tm_year starts at 1900.
         */
        res->tm_year = 2000 - 1900 + 4 * (ts / 1461);
        ts = ts % 1461;

        if (ts == 1460) {
                res->tm_year += 4;
                res->tm_mon = 1;
                res->tm_mday = 29;
                return;
        }
        res->tm_year += ts / 365;
        ts %= 365;

        /* note we're starting in march like the romans did... */
        if (ts >= 306) /* Jan 1 of next year */
                res->tm_year++;

        static time_t months[13] = {
                0, 31, 61, 92, 122, 153, 184, 214, 245, 275, 306, 337, 365,
        };
        const size_t month_max = array_size(months) - 1;

        for (size_t i = 0; i < month_max; i++) {
                if (ts < months[i + 1]) {
                        res->tm_mon = ((i + 2) % 12);
                        res->tm_mday = 1 + ts - months[i];
                        break;
                }
        }
}

/* one of the greatest advantages of this logging target:  unlike syslog(),
 * which is not AS-Safe, we can send crashlogs to syslog here.
 */
static void zlog_5424_sigsafe(struct zlog_target *zt, const char *text,
                              size_t len)
{
        static const char *const months_3164[12] = {
                "Jan", "Feb", "Mar", "Apr", "May", "Jun",
                "Jul", "Aug", "Sep", "Oct", "Nov", "Dec",
        };

        struct zlt_5424 *zte = container_of(zt, struct zlt_5424, zt);
        struct iovec iov[3], *iovp = iov;
        char buf[256];
        struct fbuf fbuf = {
                .buf = buf,
                .pos = buf,
                .len = sizeof(buf),
        };
        int fd;
        intmax_t pid = (intmax_t)getpid();
        struct tm tm;

        switch (zte->fmt) {
        case ZLOG_FMT_5424:
                gmtime_assafe(time(NULL), &tm);
                bprintfrr(
                        &fbuf,
                        "<%d>1 %04u-%02u-%02uT%02u:%02u:%02uZ - %s %jd %.*s  ",
                        zte->facility | LOG_CRIT, tm.tm_year + 1900,
                        tm.tm_mon + 1, tm.tm_mday, tm.tm_hour, tm.tm_min,
                        tm.tm_sec, zlog_progname, pid, (int)(zlog_prefixsz - 2),
                        zlog_prefix);
                break;

        case ZLOG_FMT_3164:
        case ZLOG_FMT_LOCAL:
                /* this will unfortuantely be wrong by the timezone offset
                 * if the user selected non-UTC.  But not much we can do
                 * about that...
                 */
                gmtime_assafe(time(NULL), &tm);
                bprintfrr(&fbuf, "<%d>%3s %2u %02u:%02u:%02u %s%s[%jd]: ",
                          zte->facility | LOG_CRIT, months_3164[tm.tm_mon],
                          tm.tm_mday, tm.tm_hour, tm.tm_min, tm.tm_sec,
                          (zte->fmt == ZLOG_FMT_LOCAL) ? "" : "- ",
                          zlog_progname, pid);
                break;

        case ZLOG_FMT_JOURNALD:
                bprintfrr(&fbuf,
                          "PRIORITY=%d\n"
                          "SYSLOG_FACILITY=%d\n"
                          "FRR_DAEMON=%s\n"
                          "MESSAGE=",
                          LOG_CRIT, zte->facility, zlog_progname);
                break;
        }

        iovp->iov_base = fbuf.buf;
        iovp->iov_len = fbuf.pos - fbuf.buf;
        iovp++;

        iovp->iov_base = (char *)text;
        iovp->iov_len = len;
        iovp++;

        if (zte->use_nl) {
                iovp->iov_base = (char *)"\n";
                iovp->iov_len = 1;
                iovp++;
        }

        fd = atomic_load_explicit(&zte->fd, memory_order_relaxed);

        if (!zte->sa_len)
                writev(fd, iov, iovp - iov);
        else {
                struct msghdr mh = {};

                mh.msg_name = (struct sockaddr *)&zte->sa;
                mh.msg_namelen = zte->sa_len;
                mh.msg_iov = iov;
                mh.msg_iovlen = iovp - iov;
                sendmsg(fd, &mh, 0);
        }
}

/* housekeeping & configuration */

void zlog_5424_init(struct zlog_cfg_5424 *zcf)
{
        pthread_mutex_init(&zcf->cfg_mtx, NULL);
}

static void zlog_5424_target_free(struct zlt_5424 *zlt)
{
        if (!zlt)
                return;

        rcu_close(&zlt->head_close, zlt->fd);
        rcu_free(MTYPE_LOG_5424, zlt, zt.rcu_head);
}

void zlog_5424_fini(struct zlog_cfg_5424 *zcf, bool keepopen)
{
        if (keepopen)
                zcf->active = NULL;

        if (zcf->active) {
                struct zlt_5424 *ztf;
                struct zlog_target *zt;

                zt = zlog_target_replace(&zcf->active->zt, NULL);
                ztf = container_of(zt, struct zlt_5424, zt);
                zlog_5424_target_free(ztf);
        }
        pthread_mutex_destroy(&zcf->cfg_mtx);
}

static void zlog_5424_cycle(struct zlog_cfg_5424 *zcf, int fd)
{
        struct zlog_target *old;
        struct zlt_5424 *zlt = NULL, *oldt;

        if (fd >= 0) {
                struct zlog_target *zt;

                /* all of this is swapped in by zlog_target_replace() below,
                 * the old target is RCU-freed afterwards.
                 */
                zt = zlog_target_clone(MTYPE_LOG_5424, &zcf->active->zt,
                                       sizeof(*zlt));
                zlt = container_of(zt, struct zlt_5424, zt);

                zlt->fd = fd;
                zlt->kw_version = zcf->kw_version;
                zlt->kw_location = zcf->kw_location;
                zlt->kw_uid = zcf->kw_uid;
                zlt->kw_ec = zcf->kw_ec;
                zlt->kw_args = zcf->kw_args;
                zlt->use_nl = true;
                zlt->facility = zcf->facility;

                /* DGRAM & SEQPACKET = 1 log message per packet */
                zlt->packets = (zcf->sock_type == SOCK_DGRAM) ||
                               (zcf->sock_type == SOCK_SEQPACKET);
                zlt->sa = zcf->sa;
                zlt->sa_len = zcf->sa_len;
                zlt->fmt = zcf->fmt;
                zlt->zt.prio_min = zcf->prio_min;
                zlt->zt.logfn = zlog_5424;
                zlt->zt.logfn_sigsafe = zlog_5424_sigsafe;

                switch (zcf->fmt) {
                case ZLOG_FMT_5424:
                case ZLOG_FMT_JOURNALD:
                        zlt->ts_flags = zcf->ts_flags;
                        zlt->ts_flags &= ZLOG_TS_PREC | ZLOG_TS_UTC;
                        zlt->ts_flags |= ZLOG_TS_ISO8601;
                        break;
                case ZLOG_FMT_3164:
                case ZLOG_FMT_LOCAL:
                        zlt->ts_flags = zcf->ts_flags & ZLOG_TS_UTC;
                        if (zlt->packets)
                                zlt->use_nl = false;
                        break;
                }
        }

        old = zcf->active ? &zcf->active->zt : NULL;
        old = zlog_target_replace(old, &zlt->zt);
        zcf->active = zlt;

        /* oldt->fd == fd happens for zlog_5424_apply_meta() */
        oldt = container_of(old, struct zlt_5424, zt);
        if (oldt && oldt->fd != (unsigned int)fd)
                rcu_close(&oldt->head_close, oldt->fd);
        rcu_free(MTYPE_LOG_5424, oldt, zt.rcu_head);
}

static void zlog_5424_reconnect(struct event *t)
{
        struct zlog_cfg_5424 *zcf = THREAD_ARG(t);
        int fd = THREAD_FD(t);
        char dummy[256];
        ssize_t ret;

        if (zcf->active) {
                ret = read(fd, dummy, sizeof(dummy));
                if (ret > 0) {
                        /* logger is sending us something?!?! */
                        event_add_read(t->master, zlog_5424_reconnect, zcf, fd,
                                       &zcf->t_reconnect);
                        return;
                }

                if (ret == 0)
                        zlog_warn("logging socket %pSE closed by peer",
                                  zcf->filename);
                else
                        zlog_warn("logging socket %pSE error: %m",
                                  zcf->filename);
        }

        /* do NOT close() anything here;  other threads may still be writing
         * and their messages need to be lost rather than end up on a random
         * other fd that got reassigned the same number, like a BGP session!
         */
        fd = zlog_5424_open(zcf, -1);

        frr_with_mutex (&zcf->cfg_mtx) {
                zlog_5424_cycle(zcf, fd);
        }
}

static int zlog_5424_unix(struct sockaddr_un *suna, int sock_type)
{
        int fd;
        int size = 1 * 1024 * 1024, prev_size;
        socklen_t opt_size;
        int save_errno;

        fd = socket(AF_UNIX, sock_type, 0);
        if (fd < 0)
                return -1;

        if (connect(fd, (struct sockaddr *)suna, sizeof(*suna))) {
                /* zlog_5424_open() will print the error for connect() */
                save_errno = errno;
                close(fd);
                errno = save_errno;
                return -1;
        }

        opt_size = sizeof(prev_size);
        if (getsockopt(fd, SOL_SOCKET, SO_SNDBUF, &prev_size, &opt_size))
                return fd;

        /* setsockopt_so_sendbuf() logs on error; we don't really care that
         * much here.  Also, never shrink the buffer below the initial size.
         */
        while (size > prev_size &&
               setsockopt(fd, SOL_SOCKET, SO_SNDBUF, &size, sizeof(size)) == -1)
                size /= 2;

        return fd;
}

static int zlog_5424_open(struct zlog_cfg_5424 *zcf, int sock_type)
{
        int fd = -1;
        int flags = 0;
        int err;
        socklen_t optlen;
        bool do_chown = false;
        bool need_reconnect = false;
        static const int unix_types[] = {
                SOCK_STREAM,
                SOCK_SEQPACKET,
                SOCK_DGRAM,
        };
        struct sockaddr_un sa;

        zcf->sock_type = -1;
        zcf->sa_len = 0;

        switch (zcf->dst) {
        case ZLOG_5424_DST_NONE:
                break;

        case ZLOG_5424_DST_FD:
                fd = dup(zcf->fd);

                optlen = sizeof(sock_type);
                if (!getsockopt(fd, SOL_SOCKET, SO_TYPE, &sock_type, &optlen)) {
                        zcf->sock_type = sock_type;
                        need_reconnect = (zcf->sock_type != SOCK_DGRAM);
                }
                break;

        case ZLOG_5424_DST_FIFO:
                if (!zcf->filename)
                        break;

                if (!zcf->file_nocreate) {
                        frr_with_privs (lib_privs) {
                                mode_t prevmask;

                                prevmask = umask(0777 ^ zcf->file_mode);
                                err = mkfifo(zcf->filename, 0666);
                                umask(prevmask);
                        }
                        if (err == 0)
                                do_chown = true;
                        else if (errno != EEXIST)
                                break;
                }

                flags = O_NONBLOCK;
                /* fallthru */

        case ZLOG_5424_DST_FILE:
                if (!zcf->filename)
                        break;

                frr_with_privs (lib_privs) {
                        fd = open(zcf->filename, flags | O_WRONLY | O_APPEND |
                                                         O_CLOEXEC | O_NOCTTY);
                }
                if (fd >= 0)
                        break;
                if (zcf->file_nocreate || flags) {
                        flog_err_sys(EC_LIB_SYSTEM_CALL,
                                     "could not open log file %pSE: %m",
                                     zcf->filename);
                        break;
                }

                frr_with_privs (lib_privs) {
                        mode_t prevmask;

                        prevmask = umask(0777 ^ zcf->file_mode);
                        fd = open(zcf->filename,
                                  O_WRONLY | O_APPEND | O_CLOEXEC | O_NOCTTY |
                                          O_CREAT | O_EXCL,
                                  zcf->file_mode);
                        umask(prevmask);
                }
                if (fd >= 0) {
                        do_chown = true;
                        break;
                }

                frr_with_privs (lib_privs) {
                        fd = open(zcf->filename,
                                  O_WRONLY | O_APPEND | O_CLOEXEC | O_NOCTTY);
                }
                if (fd >= 0)
                        break;

                flog_err_sys(EC_LIB_SYSTEM_CALL,
                             "could not open or create log file %pSE: %m",
                             zcf->filename);
                break;

        case ZLOG_5424_DST_UNIX:
                if (!zcf->filename)
                        break;

                memset(&sa, 0, sizeof(sa));
                sa.sun_family = AF_UNIX;
                strlcpy(sa.sun_path, zcf->filename, sizeof(sa.sun_path));

                /* check if ZLOG_5424_DST_FD needs a touch when changing
                 * something here.  the user can pass in a pre-opened unix
                 * socket through a fd at startup.
                 */
                frr_with_privs (lib_privs) {
                        if (sock_type != -1)
                                fd = zlog_5424_unix(&sa, sock_type);
                        else {
                                for (size_t i = 0; i < array_size(unix_types);
                                     i++) {
                                        fd = zlog_5424_unix(&sa, unix_types[i]);
                                        if (fd != -1) {
                                                zcf->sock_type = unix_types[i];
                                                break;
                                        }
                                }
                        }
                }
                if (fd == -1) {
                        zcf->sock_type = -1;

                        flog_err_sys(
                                EC_LIB_SYSTEM_CALL,
                                "could not connect to log unix path %pSE: %m",
                                zcf->filename);
                        need_reconnect = true;
                } else {
                        /* datagram sockets are connectionless, restarting
                         * the receiver may lose some packets but will resume
                         * working afterwards without any action from us.
                         */
                        need_reconnect = (zcf->sock_type != SOCK_DGRAM);
                }
                break;
        }

        /* viable on both DST_FD and DST_UNIX path */
        if (zcf->sock_type == SOCK_DGRAM) {
                zcf->sa_len = sizeof(zcf->sa);
                if (getpeername(fd, (struct sockaddr *)&zcf->sa,
                                &zcf->sa_len)) {
                        flog_err_sys(
                                EC_LIB_SYSTEM_CALL,
                                "could not get remote address for log socket.  logging may break if log receiver restarts.");
                        zcf->sa_len = 0;
                }
        }

        if (do_chown) {
                uid_t uid = zcf->file_uid;
                gid_t gid = zcf->file_gid;

                if (uid != (uid_t)-1 || gid != (gid_t)-1) {
                        frr_with_privs (lib_privs) {
                                err = fchown(fd, uid, gid);
                        }
                        if (err)
                                flog_err_sys(
                                        EC_LIB_SYSTEM_CALL,
                                        "failed to chown() log file %pSE: %m",
                                        zcf->filename);
                }
        }

        if (need_reconnect) {
                assert(zcf->master);

                if (fd != -1) {
                        event_add_read(zcf->master, zlog_5424_reconnect, zcf,
                                       fd, &zcf->t_reconnect);
                        zcf->reconn_backoff_cur = zcf->reconn_backoff;

                } else {
                        event_add_timer_msec(zcf->master, zlog_5424_reconnect,
                                             zcf, zcf->reconn_backoff_cur,
                                             &zcf->t_reconnect);

                        zcf->reconn_backoff_cur += zcf->reconn_backoff_cur / 2;
                        if (zcf->reconn_backoff_cur > zcf->reconn_backoff_max)
                                zcf->reconn_backoff_cur =
                                        zcf->reconn_backoff_max;
                }
        }

        return fd;
}

bool zlog_5424_apply_dst(struct zlog_cfg_5424 *zcf)
{
        int fd = -1;

        event_cancel(&zcf->t_reconnect);

        if (zcf->prio_min != ZLOG_DISABLED)
                fd = zlog_5424_open(zcf, -1);

        frr_with_mutex (&zcf->cfg_mtx) {
                zlog_5424_cycle(zcf, fd);
        }
        return fd != -1;
}


bool zlog_5424_apply_meta(struct zlog_cfg_5424 *zcf)
{
        frr_with_mutex (&zcf->cfg_mtx) {
                if (zcf->active)
                        zlog_5424_cycle(zcf, zcf->active->fd);
        }

        return true;
}

void zlog_5424_state(struct zlog_cfg_5424 *zcf, size_t *lost_msgs,
                     int *last_errno, bool *stale_errno, struct timeval *err_ts)
{
        if (lost_msgs)
                *lost_msgs =
                        zcf->active
                                ? atomic_load_explicit(&zcf->active->lost_msgs,
                                                       memory_order_relaxed)
                                : 0;
        if (last_errno)
                *last_errno = zcf->active ? zcf->active->last_err : 0;
        if (stale_errno)
                *stale_errno = zcf->active ? !zcf->active->current_err : 0;
        if (err_ts && zcf->active)
                *err_ts = zcf->active->last_err_ts;
}

struct rcu_close_rotate {
        struct rcu_head_close head_close;
        struct rcu_head head_self;
};

bool zlog_5424_rotate(struct zlog_cfg_5424 *zcf)
{
        struct rcu_close_rotate *rcr;
        int fd;

        frr_with_mutex (&zcf->cfg_mtx) {
                if (!zcf->active)
                        return true;

                event_cancel(&zcf->t_reconnect);

                /* need to retain the socket type because it also influences
                 * other fields (packets) and we can't atomically swap these
                 * out.  But we really want the atomic swap so we neither lose
                 * nor duplicate log messages, particularly for file targets.
                 *
                 * (zlog_5424_apply_dst / zlog_target_replace will cause
                 * duplicate log messages if another thread logs something
                 * while we're right in the middle of swapping out the log
                 * target)
                 */
                fd = zlog_5424_open(zcf, zcf->sock_type);
                if (fd < 0)
                        return false;

                fd = atomic_exchange_explicit(&zcf->active->fd,
                                              (uint_fast32_t)fd,
                                              memory_order_relaxed);
        }

        rcr = XCALLOC(MTYPE_LOG_5424_ROTATE, sizeof(*rcr));
        rcu_close(&rcr->head_close, fd);
        rcu_free(MTYPE_LOG_5424_ROTATE, rcr, head_self);

        return true;
}