libmapid/common/mapid.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright (c) 2004, 2010, Oracle and/or its affiliates. All rights reserved.
 */

/*
 * PSARC/2004/154 nfsmapid DNS enhancements implementation.
 *
 * As per RFC 3530, file owner and group attributes in version 4 of the
 * NFS protocol are no longer exchanged between client and server as 32
 * bit integral values. Instead, owner and group file attributes are
 * exchanged between client and server as UTF8 strings of form
 *
 *      'user@domain'       (ie. "joeblow@central.sun.com")
 *      'group@domain'      (ie. "staff@central.sun.com")
 *
 * This NFSv4 feature is far beyond anything NFSv2/v3 ever provided, as
 * being able to describe a user with a unique string identifier provides
 * a much more powerful and administrative friendly way of dealing with
 * overlaps in the uid/gid number spaces. That notwithstanding, dealing
 * with issues of correctly mapping user and group ownership in a cross-
 * domain environment has proven a difficult problem to solve, since
 * dealing with different permutations of client naming configurations
 * (ie. NIS only, LDAP only, etc.) have bloated the problem. Thus, users
 * utilizing clients and servers that have the 'domain' portion of the
 * UTF8 attribute string configured differently than its peer server and
 * client accordingly, will experience watching their files owned by the
 * 'nobody' user and group. This is due to the fact that the 'domain's
 * don't match and the nfsmapid daemon treats the attribute strings as
 * unknown user(s) or group(s) (even though the actual uid/gid's may exist
 * in the executing daemon's system). Please refer to PSARC/2004/154 for
 * further background and motivation for these enhancements.
 *
 * The latest implementation of the nfsmapid daemon relies on a DNS TXT
 * record. The behavior of nfsmapid is to first use the NFSMAPID_DOMAIN
 * configuration option in /etc/default/nfs. If the option has not been
 * set, then the nfsmapid daemon queries the configured DNS domain server
 * for the _nfsv4idmapdomain TXT record. If the record exists, then the
 * record's value is used as the 'domain' portion of the UTF8 attribute
 * strings. If the TXT record has not been configured in the DNS server,
 * then the daemon falls back to using the DNS domain name itself as the
 * 'domain' portion of the attribute strings. Lastly, if the configured
 * DNS server is unresponsive, the nfsmapid daemon falls back to using
 * the DNS domain name as the 'domain' portion of the attribute strings,
 * and fires up a query thread to keep contacting the DNS server until
 * it responds with either a TXT record, or a lack thereof, in which
 * case, nfsmapid just continues to utilize the DNS domain name.
 */
#define __LIBMAPID_IMPL
#include <nfs/mapid.h>
#include <libshare.h>
#include <libscf.h>
#include <limits.h>
#include <rpcsvc/daemon_utils.h>
#include "smfcfg.h"

#pragma init(_lib_init)
#pragma fini(_lib_fini)

/*
 * DEBUG Only
 * Decode any resolver errors and print out message to log
 */
static int
resolv_error(void)
{
#ifndef DEBUG

    return (h_errno);

#else   /* DEBUG */

    static uint64_t  msg_done[NS_ERRS] = {0};

    switch (h_errno) {
    case NETDB_INTERNAL:
        syslog(LOG_ERR, EMSG_NETDB_INTERNAL, strerror(errno));
        break;

    case HOST_NOT_FOUND:
        (void) rw_rdlock(&s_dns_impl_lock);
        msg_done[h_errno]++;
        if (!(msg_done[h_errno] % NFSMAPID_SLOG_RATE))
            syslog(LOG_ERR, EMSG_HOST_NOT_FOUND, s_dname);
        (void) rw_unlock(&s_dns_impl_lock);
        break;

    case TRY_AGAIN:
        /*
         * Nameserver is not responding.
         * Try again after a given timeout.
         */
        (void) rw_rdlock(&s_dns_impl_lock);
        msg_done[h_errno]++;
        if (!(msg_done[h_errno] % NFSMAPID_SLOG_RATE))
            syslog(LOG_ERR, EMSG_TRY_AGAIN, s_dname);
        (void) rw_unlock(&s_dns_impl_lock);
        break;

    case NO_RECOVERY:
        /*
         * This msg only really happens once, due
         * to s_dns_disabled flag (see below)
         */
        syslog(LOG_ERR, EMSG_NO_RECOVERY, hstrerror(h_errno));
        break;

    case NO_DATA:
        /*
         * No entries in the nameserver for
         * the specific record or record type.
         */
        (void) rw_rdlock(&s_dns_impl_lock);
        msg_done[h_errno]++;
        if (!(msg_done[h_errno] % NFSMAPID_SLOG_RATE))
            syslog(LOG_ERR, EMSG_NO_DATA, NFSMAPID_DNS_RR, s_dname);
        (void) rw_unlock(&s_dns_impl_lock);
        break;

    case NETDB_SUCCESS:
    default:
        break;
    }
    return (h_errno);

#endif  /* DEBUG */
}

/*
 * Reset the global state variables used for the TXT record.
 * Having these values reset to zero helps nfsmapid confirm
 * that a valid DNS TXT record was not found; in which case,
 * it would fall back to using the configured DNS domain name.
 *
 * If a valid DNS TXT record _was_ found, but subsequent contact
 * to the DNS server is somehow hindered, the previous DNS TXT
 * RR value continues to be used. Thus, in such instances, we
 * forego clearing the global config variables so nfsmapid can
 * continue to use a valid DNS TXT RR while contact to the DNS
 * server is reestablished.
 */
static void
resolv_txt_reset(void)
{
    (void) rw_wrlock(&s_dns_impl_lock);
    bzero(s_txt_rr, sizeof (s_txt_rr));
    (void) rw_unlock(&s_dns_impl_lock);

    (void) rw_wrlock(&s_dns_data_lock);
    if (!dns_txt_cached) {
        dns_txt_domain_len = 0;
        bzero(dns_txt_domain, DNAMEMAX);
    }
    (void) rw_unlock(&s_dns_data_lock);
}

/*
 * Initialize resolver and populate &s_res struct
 *
 * DNS Domain is saved off sysdns_domain in case we
 * need to fall back to using the DNS domain name as
 * the v4 attribute string domain.
 */
static int
resolv_init(void)
{
    size_t          len;
    int         n;
    struct __res_state  res;

    (void) mutex_lock(&s_res_lock);
    bzero(&s_res, sizeof (struct __res_state));
    n = h_errno = errno = 0;
    if ((n = res_ninit(&s_res)) < 0) {
        (void) mutex_unlock(&s_res_lock);
        (void) resolv_error();
        return (n);
    }
    res = s_res;
    (void) mutex_unlock(&s_res_lock);

    len = strlen(res.defdname) + 1;
    (void) rw_wrlock(&s_dns_impl_lock);
    bzero(s_dname, sizeof (s_dname));
    (void) snprintf(s_dname, len, "%s", res.defdname);
    (void) rw_unlock(&s_dns_impl_lock);

    (void) rw_wrlock(&s_dns_data_lock);
    (void) snprintf(sysdns_domain, len, "%s", res.defdname);
    (void) rw_unlock(&s_dns_data_lock);

    return (0);
}

/*
 * Search criteria assumptions:
 *
 * The onus will fall on the sysadmins to correctly configure the TXT
 * record in the DNS domain where the box currently resides in order
 * for the record to be found. However, if they sysadmin chooses to
 * add the 'search' key to /etc/resolv.conf, then resolv_search()
 * _will_ traverse up the DNS tree as specified in the 'search' key.
 * Otherwise, we'll default the domain to the DNS domain itself.
 */
static int
resolv_search(void)
{
    int         len;
    ans_t           ans = {0};
    struct __res_state  res;
    int         type = T_TXT;
    int         class = C_IN;

    (void) mutex_lock(&s_res_lock);
    res = s_res;
    (void) mutex_unlock(&s_res_lock);

    /*
     * Avoid holding locks across the res_nsearch() call to
     * prevent stalling threads during network partitions.
     */
    len = h_errno = errno = 0;
    if ((len = res_nsearch(&res, NFSMAPID_DNS_RR, class, type,
        ans.buf, sizeof (ans))) < 0)
        return (resolv_error());

    (void) rw_wrlock(&s_dns_impl_lock);
    s_ans = ans;
    s_anslen = len;
    (void) rw_unlock(&s_dns_impl_lock);

    return (NETDB_SUCCESS);
}

/*
 * Free all resolver state information stored in s_res
 */
static void
resolv_destroy(void)
{
    (void) mutex_lock(&s_res_lock);
    res_ndestroy(&s_res);
    (void) mutex_unlock(&s_res_lock);
}

/*
 * Skip one DNS record
 */
static uchar_t  *
resolv_skip_rr(uchar_t *p, uchar_t *eom)
{
    int t;
    int dlen;

    /*
     * Skip compressed name
     */
    errno = 0;
    if ((t = dn_skipname(p, eom)) < 0) {
#ifdef  DEBUG
        syslog(LOG_ERR, "%s", strerror(errno));
#endif
        return (NULL);
    }

    /*
     * Advance pointer and make sure
     * we're still within the message
     */
    p += t;
    if ((p + RRFIXEDSZ) > eom)
        return (NULL);

    /*
     * Now, just skip over the rr fields
     */
    p += INT16SZ;   /* type */
    p += INT16SZ;   /* class */
    p += INT32SZ;   /* ttl */
    dlen = ns_get16(p);
    p += INT16SZ;
    p += dlen;  /* dlen */
    if (p > eom)
        return (NULL);

    return (p);
}

/*
 * Process one TXT record.
 *
 * nfsmapid queries the DNS server for the specific _nfsv4idmapdomain
 * TXT record. Thus, if the TXT record exists, the answer section of
 * the DNS response carries the TXT record's value. Thus, we check that
 * the value is indeed a valid domain and set the modular s_txt_rr
 * global to the domain value.
 */
static void
resolve_process_txt(uchar_t *p, int dlen)
{
    char        *rr_base = (char *)(p + 1);
    char        *rr_end = (char *)(p + dlen);
    size_t       len = rr_end - rr_base;
#ifdef  DEBUG
    static uint64_t  msg_done = 0;
#endif
    char         tmp_txt_rr[DNAMEMAX];

    if (len >= DNAMEMAX)
        return;     /* process next TXT RR */

    /*
     * make sure we have a clean buf since
     * we may've processed several TXT rr's
     */
    (void) rw_wrlock(&s_dns_impl_lock);
    bzero(s_txt_rr, sizeof (s_txt_rr));
    (void) rw_unlock(&s_dns_impl_lock);

    (void) strncpy(tmp_txt_rr, rr_base, len);
    tmp_txt_rr[len] = '\0';

    /*
     * If there is a record and it's a valid domain, we're done.
     */
    if (rr_base[0] != '\0' && mapid_stdchk_domain(tmp_txt_rr) > 0) {
        (void) rw_wrlock(&s_dns_impl_lock);
        (void) strncpy(s_txt_rr, rr_base, len);
        (void) rw_unlock(&s_dns_impl_lock);
#ifdef  DEBUG
        syslog(LOG_ERR, "TXT (Rec):\t%s", s_txt_rr);

    } else if (!(msg_done++ % NFSMAPID_SLOG_RATE)) {
        /*
         * Otherwise, log the error
         */
        (void) rw_rdlock(&s_dns_impl_lock);
        syslog(LOG_ERR, EMSG_DNS_RR_INVAL, NFSMAPID_DNS_RR, s_dname);
        (void) rw_unlock(&s_dns_impl_lock);
#endif
    }
}

/*
 * Decode any answer received from the DNS server. This interface is
 * capable of much more than just decoding TXT records. We maintain
 * focus on TXT rr's for now, but this will probably change once we
 * get the IETF approved application specific DNS RR.
 *
 * Here's an example of the TXT record we're decoding (as would appear
 * in the DNS zone file):
 *
 *            _nfsv4idmapdomain    IN    TXT    "sun.com"
 *
 * Once the IETF application specific DNS RR is granted, we should only
 * be changing the record flavor, but all should pretty much stay the
 * same.
 */
static void
resolv_decode(void)
{
    uchar_t     *buf;
    HEADER      *hp;
    uchar_t      name[DNAMEMAX];
    uchar_t     *eom;
    uchar_t     *p;
    int      n;
    uint_t       qd_cnt;
    uint_t       an_cnt;
    uint_t       ns_cnt;
    uint_t       ar_cnt;
    uint_t       cnt;
    uint_t       type;
    int      dlen;
    ans_t        answer = {0};
    int      answer_len = 0;

    /*
     * Check the HEADER for any signs of errors
     * and extract the answer counts for later.
     */
    (void) rw_rdlock(&s_dns_impl_lock);
    answer = s_ans;
    answer_len = s_anslen;
    (void) rw_unlock(&s_dns_impl_lock);

    buf = (uchar_t *)&answer.buf;
    hp = (HEADER *)&answer.hdr;
    eom = (uchar_t *)(buf + answer_len);
    if (hp->rcode !=  NOERROR) {
#ifdef  DEBUG
        syslog(LOG_ERR, "errno: %s", strerror(errno));
        syslog(LOG_ERR, "h_errno: %s", hstrerror(h_errno));
#endif
        return;
    }
    qd_cnt = ntohs(hp->qdcount);
    an_cnt = ntohs(hp->ancount);
    ns_cnt = ntohs(hp->nscount);
    ar_cnt = ntohs(hp->arcount);

    /*
     * skip query entries
     */
    p = (uchar_t *)(buf + HFIXEDSZ);
    errno = 0;
    while (qd_cnt-- > 0) {
        n = dn_skipname(p, eom);
        if (n < 0) {
#ifdef  DEBUG
            syslog(LOG_ERR, "%s", strerror(errno));
#endif
            return;
        }
        p += n;
        p += INT16SZ;   /* type */
        p += INT16SZ;   /* class */
    }

#ifdef  DEBUG
    /*
     * If debugging... print query only once.
     * NOTE: Don't advance pointer... this is done
     *   in while() loop on a per record basis !
     */
    n = h_errno = errno = 0;
    n = dn_expand(buf, eom, p, (char *)name, sizeof (name));
    if (n < 0) {
        (void) resolv_error();
        return;
    }
    syslog(LOG_ERR, "Query:\t\t%-30s", name);
#endif

    /*
     * Process actual answer(s).
     */
    cnt = an_cnt;
    while (cnt-- > 0 && p < eom) {
        /* skip the name field */
        n = dn_expand(buf, eom, p, (char *)name, sizeof (name));
        if (n < 0) {
            (void) resolv_error();
            return;
        }
        p += n;

        if ((p + 3 * INT16SZ + INT32SZ) > eom)
            return;

        type = ns_get16(p);
        p += INT16SZ;
        p += INT16SZ + INT32SZ; /* skip class & ttl */
        dlen = ns_get16(p);
        p += INT16SZ;

        if ((p + dlen) > eom)
            return;

        switch (type) {
            case T_TXT:
                resolve_process_txt(p, dlen);
                break;

            default:
                /*
                 * Advance to next answer record for any
                 * other record types. Again, this will
                 * probably change (see block comment).
                 */
                p += dlen;
                break;
        }
    }

    /*
     * Skip name server and additional records for now.
     */
    cnt = ns_cnt + ar_cnt;
    if (cnt > 0) {
        while (--cnt != 0 && p < eom) {
            p = resolv_skip_rr(p, eom);
            if (p == NULL)
                return;
        }
    }
}

/*
 * If a valid TXT record entry exists, s_txt_rr contains the domain
 * value (as set in resolv_process_txt) and we extract the value into
 * dns_txt_domain (the exported global). If there was _no_ valid TXT
 * entry, we simply return and check_domain() will default to the
 * DNS domain since we did resolv_txt_reset() first.
 */
static void
resolv_get_txt_data()
{
    (void) rw_rdlock(&s_dns_impl_lock);
    if (s_txt_rr[0] != '\0') {
        (void) rw_wrlock(&s_dns_data_lock);
        (void) snprintf(dns_txt_domain, strlen(s_txt_rr) + 1, "%s",
            s_txt_rr);
        dns_txt_domain_len = strlen(dns_txt_domain);
        dns_txt_cached = 1;
        (void) rw_unlock(&s_dns_data_lock);
    }
    (void) rw_unlock(&s_dns_impl_lock);
}

static void
domain_sync(cb_t *argp, char *dname)
{
    int dlen = 0;
    void    *(*fcn)(void *) = NULL;
    int sighup = 0;
    int domchg = 0;

    /*
     * Make sure values passed are sane and initialize accordingly.
     */
    if (dname != NULL)
        dlen = strlen(dname);
    if (argp) {
        if (argp->fcn)
            fcn = argp->fcn;
        if (argp->signal)
            sighup = argp->signal;
    }

    /*
     * Update the library's mapid_domain variable if 'dname' is different.
     */
    if (dlen != 0 && strncasecmp(dname, mapid_domain, NS_MAXCDNAME)) {
        (void) rw_wrlock(&mapid_domain_lock);
        (void) strncpy(mapid_domain, dname, NS_MAXCDNAME);
        mapid_domain_len = dlen;
        (void) rw_unlock(&mapid_domain_lock);
        domchg++;
    }

    /*
     * If the caller gave us a valid callback routine, we
     * instantiate it to announce the domain change, but
     * only if either the domain changed _or_ the caller
     * was issued a SIGHUP.
     */
    if (fcn != NULL && (sighup || domchg))
        (void) fcn((void *)mapid_domain);
}

/*
 * Thread to keep pinging  DNS  server for  TXT  record if nfsmapid's
 * initial attempt at contact with server failed. We could potentially
 * have a substantial number of NFSv4 clients and having all of them
 * hammering on an already unresponsive DNS server would not help
 * things. So, we limit the number of live query threads to at most
 * 1 at any one time to keep things from getting out of hand.
 */
/* ARGSUSED */
static void *
resolv_query_thread(void *arg)
{
    unsigned int     nap_time;

#ifdef  DEBUG
    char        *whoami = "query_thread";

    syslog(LOG_ERR, "%s active !", whoami);
#endif
    (void) rw_rdlock(&s_dns_impl_lock);
    nap_time = s_dns_tout;
    (void) rw_unlock(&s_dns_impl_lock);

    for (;;) {
        (void) sleep(nap_time);

        resolv_txt_reset();
        if (resolv_init() < 0) {
            /*
             * Failed to initialize resolver. Do not
             * query DNS server.
             */
            goto thr_reset;
        }
        switch (resolv_search()) {
        case NETDB_SUCCESS:
            resolv_decode();
            resolv_get_txt_data();

            /*
             * This is a bit different than what we
             * do in get_dns_txt_domain(), where we
             * simply return and let the caller
             * access dns_txt_domain directly.
             *
             * Here we invoke the callback routine
             * provided by the caller to the
             * mapid_reeval_domain() interface via
             * the cb_t's fcn param.
             */
            domain_sync((cb_t *)arg, dns_txt_domain);
            goto thr_okay;

        case NO_DATA:
            /*
             * DNS is up now, but does not have
             * the NFSV4IDMAPDOMAIN TXT record.
             */
#ifdef  DEBUG
            syslog(LOG_ERR, "%s: DNS has no TXT Record", whoami);
#endif
            goto thr_reset;

        case NO_RECOVERY:
            /*
             * Non-Recoverable error occurred. No sense
             * in keep pinging the DNS server at this
             * point, so we disable any further contact.
             */
#ifdef  DEBUG
            syslog(LOG_ERR, EMSG_DNS_DISABLE, whoami);
#endif
            (void) rw_wrlock(&s_dns_impl_lock);
            s_dns_disabled = TRUE;
            (void) rw_unlock(&s_dns_impl_lock);
            goto thr_reset;

        case HOST_NOT_FOUND:
            /*
             * Authoritative NS not responding...
             * keep trying for non-authoritative reply
             */
            /*FALLTHROUGH*/

        case TRY_AGAIN:
            /* keep trying */
#ifdef  DEBUG
            syslog(LOG_ERR, "%s: retrying...", whoami);
#endif
            break;

        case NETDB_INTERNAL:
        default:
#ifdef  DEBUG
            syslog(LOG_ERR, "%s: Internal resolver error: %s",
                whoami, strerror(errno));
#endif
            goto thr_reset;
        }

        resolv_destroy();
    }
thr_reset:
    (void) rw_wrlock(&s_dns_data_lock);
    dns_txt_cached = 0;
    (void) rw_unlock(&s_dns_data_lock);
    resolv_txt_reset();

thr_okay:
    resolv_destroy();
    /* mark thread as done */
    (void) rw_wrlock(&s_dns_impl_lock);
    s_dns_qthr_created = FALSE;
    (void) rw_unlock(&s_dns_impl_lock);

    (void) thr_exit(NULL);
    /*NOTREACHED*/
    return (NULL);
}

/*
 * nfsmapid's interface into the resolver for getting the TXT record.
 *
 * Key concepts:
 *
 * o If the DNS server is available and the TXT record is found, we
 *   simply decode the output and fill the exported dns_txt_domain
 *   global, so our caller can configure the daemon appropriately.
 *
 * o If the TXT record is not found, then having done resolv_txt_reset()
 *   first will allow our caller to recognize that the exported globals
 *   are empty and thus configure nfsmapid to use the default DNS domain.
 *
 * o Having no /etc/resolv.conf file is pretty much a show stopper, since
 *   there is no name server address information. We return since we've
 *   already have reset the TXT global state.
 *
 * o If a previous call to the DNS server resulted in an unrecoverable
 *   error, then we disable further contact to the DNS server and return.
 *   Having the TXT global state already reset guarantees that our caller
 *   will fall back to the right configuration.
 *
 * o Query thread creation is throttled by s_dns_qthr_created. We mitigate
 *   the problem of an already unresponsive DNS server by allowing at most
 *   1 outstanding query thread since we could potentially have a substantial
 *   amount of clients hammering on the same DNS server attempting to get
 *   the TXT record.
 */
static void
get_dns_txt_domain(cb_t *argp)
{
    int     err;
#ifdef  DEBUG
    static uint64_t msg_done = 0;
    char        *whoami = "get_dns_txt_domain";
#endif
    long        thr_flags = THR_DETACHED;
    struct stat st;

    /*
     * We reset TXT variables first in case /etc/resolv.conf
     * is missing or we've had unrecoverable resolver errors,
     * we'll default to get_dns_domain(). If a previous DNS
     * TXT RR was found, don't clear it until we're certain
     * that contact can be made to the DNS server (see block
     * comment atop resolv_txt_reset). If we're responding to
     * a SIGHUP signal, force a reset of the cached copy.
     */
    if (argp && argp->signal) {
        (void) rw_wrlock(&s_dns_data_lock);
        dns_txt_cached = 0;
        (void) rw_unlock(&s_dns_data_lock);
    }
    resolv_txt_reset();

    errno = 0;
    if (stat(_PATH_RESCONF, &st) < 0 && errno == ENOENT) {
        /*
         * If /etc/resolv.conf is not there, then we'll
         * get the domain from domainname(1M). No real
         * reason to query DNS or fire a thread since we
         * have no nameserver addresses.
         */
        (void) rw_wrlock(&s_dns_data_lock);
        dns_txt_cached = 0;
        (void) rw_unlock(&s_dns_data_lock);
        resolv_txt_reset();
        return;
    }

    (void) rw_rdlock(&s_dns_impl_lock);
    if (s_dns_disabled) {
        /*
         * If there were non-recoverable problems with DNS,
         * we have stopped querying DNS entirely. See
         * NO_RECOVERY clause below.
         */
#ifdef  DEBUG
        syslog(LOG_ERR, "%s: DNS queries disabled", whoami);
#endif
        (void) rw_unlock(&s_dns_impl_lock);
        return;
    }
    (void) rw_unlock(&s_dns_impl_lock);

    if (resolv_init() < 0) {
        /*
         * Failed to initialize resolver. Do not
         * query DNS server.
         */
        (void) rw_wrlock(&s_dns_data_lock);
        dns_txt_cached = 0;
        (void) rw_unlock(&s_dns_data_lock);
        resolv_txt_reset();
        return;
    }
    switch (resolv_search()) {
    case NETDB_SUCCESS:
        /*
         * If there _is_ a TXT record, we let
         * our caller set the global state.
         */
        resolv_decode();
        resolv_get_txt_data();
        break;

    case TRY_AGAIN:
        if (argp == NULL || argp->fcn == NULL)
            /*
             * If no valid argument was passed or
             * callback defined, don't fire thread
             */
            break;

        (void) rw_wrlock(&s_dns_impl_lock);
        if (s_dns_qthr_created) {
            /*
             * We may have lots of clients, so we don't
             * want to bog down the DNS server with tons
             * of requests... lest it becomes even more
             * unresponsive, so limit 1 thread to query
             * DNS at a time.
             */
#ifdef  DEBUG
            syslog(LOG_ERR, "%s: query thread already active",
                whoami);
#endif
            (void) rw_unlock(&s_dns_impl_lock);
            break;
        }

        /*
         * DNS did not respond ! Set timeout and kick off
         * thread to try op again after s_dns_tout seconds.
         * We've made sure that we don't have an already
         * running thread above.
         */
        s_dns_tout = NFSMAPID_DNS_TOUT_SECS;
        err = thr_create(NULL, 0, resolv_query_thread, (void *)argp,
            thr_flags, &s_dns_qthread);
        if (!err) {
            s_dns_qthr_created = TRUE;
        }
#ifdef DEBUG
        else {
            msg_done++;
            if (!(msg_done % NFSMAPID_SLOG_RATE))
                syslog(LOG_ERR, EMSG_DNS_THREAD_ERROR);
        }
#endif
        (void) rw_unlock(&s_dns_impl_lock);
        break;

    case NO_RECOVERY:
#ifdef  DEBUG
        syslog(LOG_ERR, EMSG_DNS_DISABLE, whoami);
#endif
        (void) rw_wrlock(&s_dns_impl_lock);
        s_dns_disabled = TRUE;
        (void) rw_unlock(&s_dns_impl_lock);

        /*FALLTHROUGH*/

    default:
        /*
         * For any other errors... DNS is responding, but
         * either it has no data, or some other problem is
         * occuring. At any rate, the TXT domain should not
         * be used, so we default to the DNS domain.
         */
        (void) rw_wrlock(&s_dns_data_lock);
        dns_txt_cached = 0;
        (void) rw_unlock(&s_dns_data_lock);
        resolv_txt_reset();
        break;
    }

    resolv_destroy();
}

static int
get_mtime(const char *fname, timestruc_t *mtim)
{
    struct stat st;
    int err;

    if ((err = stat(fname, &st)) != 0)
        return (err);

    *mtim = st.st_mtim;
    return (0);
}


/*
 * trim_wspace is a destructive interface; it is up to
 * the caller to save off an original copy if needed.
 */
static char *
trim_wspace(char *dp)
{
    char    *r;
    char    *ndp;

    /*
     * Any empty domain is not valid
     */
    if (dp == NULL)
        return (NULL);

    /*
     * Skip leading blanks
     */
    for (ndp = dp; *ndp != '\0'; ndp++) {
        if (!isspace(*ndp))
            break;
    }

    /*
     * If we reached the end of the string w/o
     * finding a non-blank char, return error
     */
    if (*ndp == '\0')
        return (NULL);

    /*
     * Find next blank in string
     */
    for (r = ndp; *r != '\0'; r++) {
        if (isspace(*r))
            break;
    }

    /*
     * No more blanks found, we are done
     */
    if (*r == '\0')
        return (ndp);

    /*
     * Terminate string at blank
     */
    *r++ = '\0';

    /*
     * Skip any trailing spaces
     */
    while (*r != '\0') {
        /*
         * If a non-blank is found, it is an
         * illegal domain (embedded blanks).
         */
        if (!isspace(*r))
            return (NULL);
        r++;
    }
    return (ndp);
}

static void
get_nfs_domain(void)
{
    char value[NS_MAXCDNAME];
    int ret, bufsz = NS_MAXCDNAME;

    /*
     * Get NFSMAPID_DOMAIN property value from SMF.
     */
    bzero(value, NS_MAXCDNAME);
    ret = nfs_smf_get_prop("nfsmapid_domain", value, DEFAULT_INSTANCE,
        SCF_TYPE_ASTRING, NFSMAPID, &bufsz);
    if (ret == SA_OK && *value != NULL) {
        char *dp = NULL;
#ifdef DEBUG
        char    *whoami = "get_nfs_domain";
        char    orig[NS_MAXCDNAME] = {0};
        (void) strncpy(orig, value, NS_MAXCDNAME);
#endif
        /*
         * NFSMAPID_DOMAIN was set, so it's time for validation. If
         * it's okay, then update NFS domain and return. If not,
         * bail (syslog in DEBUG). We make nfsmapid more a bit
         * more forgiving of trailing and leading white space.
         */
        if ((dp = trim_wspace(value)) != NULL) {
            if (mapid_stdchk_domain(dp) > 0) {
                nfs_domain_len = strlen(dp);
                (void) strncpy(nfs_domain, dp, NS_MAXCDNAME);
                nfs_domain[NS_MAXCDNAME] = '\0';
                return;
            }
        }
#ifdef  DEBUG
        if (orig[0] != '\0') {
            syslog(LOG_ERR, gettext("%s: Invalid domain name \"%s\""
                " found in SMF."), whoami, orig);
        }
#endif
    }
    /*
     * So the NFS SMF parameter nfsmapid_domain cannot be obtained or
     * there is an invalid nfsmapid_domain property value.
     * Time to zap current NFS domain info.
     */
    ZAP_DOMAIN(nfs);
}

static void
get_dns_domain(void)
{
    timestruc_t  ntime = {0};

    /*
     * If we can't get stats for the config file, then
     * zap the DNS domain info.  If mtime hasn't changed,
     * then there's no work to do, so just return.
     */
    errno = 0;
    if (get_mtime(_PATH_RESCONF, &ntime) != 0) {
        switch (errno) {
            case ENOENT:
                /*
                 * The resolver defaults to obtaining the
                 * domain off of the NIS domainname(1M) if
                 * /etc/resolv.conf does not exist, so we
                 * move forward.
                 */
                break;

            default:
                ZAP_DOMAIN(dns);
                return;
        }
    } else if (TIMESTRUC_EQ(ntime, dns_mtime))
        return;

    /*
     * Re-initialize resolver to zap DNS domain from previous
     * resolv_init() calls.
     */
    (void) resolv_init();

    /*
     * Update cached DNS domain.  No need for validation since
     * domain comes from resolver.  If resolver doesn't return the
     * domain, then zap the DNS domain.  This shouldn't ever happen,
     * and if it does, the machine has bigger problems (so no need
     * to generate a message that says DNS appears to be broken).
     */
    (void) rw_rdlock(&s_dns_data_lock);
    if (sysdns_domain[0] != '\0') {
        (void) strncpy(dns_domain, sysdns_domain, NS_MAXCDNAME);
        dns_domain_len = strlen(sysdns_domain);
        (void) rw_unlock(&s_dns_data_lock);
        dns_mtime = ntime;
        resolv_destroy();
        return;
    }
    (void) rw_unlock(&s_dns_data_lock);

    ZAP_DOMAIN(dns);

    resolv_destroy();

}

/*
 * PSARC 2005/487 Contracted Sun Private Interface
 * mapid_stdchk_domain()
 * Changes must be reviewed by Solaris File Sharing
 * Changes must be communicated to contract-2005-487-01@sun.com
 *
 * Based on the recommendations from RFC1033 and RFC1035, check
 * if a given domain name string is valid. Return values are:
 *
 *       1 = valid domain name
 *       0 = invalid domain name (or invalid embedded character)
 *      -1 = domain length > NS_MAXCDNAME
 */
int
mapid_stdchk_domain(const char *ds)
{
    int i;
    size_t  len;

    if (ds[0] == '\0')
        return (0);
    else
        len = strlen(ds) - 1;

    /*
     * 1st _AND_ last char _must_ be alphanumeric.
     * We check for other valid chars below.
     */
    if ((!isalpha(ds[0]) && !isdigit(ds[0])) ||
        (!isalpha(ds[len]) && !isdigit(ds[len])))
        return (0);

    for (i = 0; *ds && i <= NS_MAXCDNAME; i++, ds++) {
        if (!isalpha(*ds) && !isdigit(*ds) &&
            (*ds != '.') && (*ds != '-') && (*ds != '_'))
            return (0);
    }
    return (i == (NS_MAXCDNAME + 1) ? -1 : 1);
}

/*
 * PSARC 2005/487 Consolidation Private
 * mapid_reeval_domain()
 * Changes must be reviewed by Solaris File Sharing
 */
void
mapid_reeval_domain(cb_t *arg)
{
    char    *domain = NULL;

    get_nfs_domain();
    if (nfs_domain_len != 0) {
        domain = nfs_domain;
        goto dsync;
    }

    get_dns_txt_domain(arg);
    if (dns_txt_domain_len != 0)
        domain = dns_txt_domain;
    else {
        /*
         * We're either here because:
         *
         *  . NFSMAPID_DOMAIN was not set in /etc/default/nfs
         *  . No suitable DNS TXT resource record exists
         *  . DNS server is not responding to requests
         *
         * in either case, we want to default to using the
         * system configured DNS domain. If this fails, then
         * dns_domain will be empty and dns_domain_len will
         * be 0.
         */
        get_dns_domain();
        domain = dns_domain;
    }

dsync:
    domain_sync(arg, domain);
}

/*
 * PSARC 2005/487 Consolidation Private
 * mapid_get_domain()
 * Changes must be reviewed by Solaris File Sharing
 *
 * The use of TSD in mapid_get_domain() diverges slightly from the typical
 * TSD use, since here, the benefit of doing TSD is mostly to allocate
 * a per-thread buffer that will be utilized by other up-calls to the
 * daemon.
 *
 * In doors, the thread used for the upcall never really exits, hence
 * the typical destructor function defined via thr_keycreate() will
 * never be called. Thus, we only use TSD to allocate the per-thread
 * buffer and fill it up w/the configured 'mapid_domain' on each call.
 * This still alleviates the problem of having the caller free any
 * malloc'd space.
 */
char *
mapid_get_domain(void)
{
    void    *tsd = NULL;

    (void) thr_getspecific(s_thr_key, &tsd);
    if (tsd == NULL) {
        tsd = malloc(NS_MAXCDNAME+1);
        if (tsd != NULL) {
            (void) rw_rdlock(&mapid_domain_lock);
            (void) strncpy((char *)tsd, mapid_domain, NS_MAXCDNAME);
            (void) rw_unlock(&mapid_domain_lock);
            (void) thr_setspecific(s_thr_key, tsd);
        }
    } else {
        (void) rw_rdlock(&mapid_domain_lock);
        (void) strncpy((char *)tsd, mapid_domain, NS_MAXCDNAME);
        (void) rw_unlock(&mapid_domain_lock);
    }
    return ((char *)tsd);
}

/*
 * PSARC 2005/487 Contracted Sun Private Interface
 * mapid_derive_domain()
 * Changes must be reviewed by Solaris File Sharing
 * Changes must be communicated to contract-2005-487-01@sun.com
 *
 * This interface is called solely via sysidnfs4 iff no
 * NFSMAPID_DOMAIN was found. So, there is no ill effect
 * of having the reeval function call get_nfs_domain().
 */
char *
mapid_derive_domain(void)
{
    cb_t    cb = {0};

    _lib_init();
    mapid_reeval_domain(&cb);
    return (mapid_get_domain());
}

void
_lib_init(void)
{
    (void) resolv_init(); /* May fail! */
    (void) rwlock_init(&mapid_domain_lock, USYNC_THREAD, NULL);
    (void) thr_keycreate(&s_thr_key, NULL);
    lib_init_done++;
    resolv_destroy();
}

void
_lib_fini(void)
{
    resolv_destroy();
}