/*
 * 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 2008 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*
 * This module adds support to the RCM framework for mounted filesystems.
 *
 * The module provides this functionality:
 *      1) reports device usage for mounted filesystems
 *      2) prevents offline operations for mounted resources
 *      3) prevents suspend operations (unless forced) of those filesystems
 *         deemed critical for the continued operation of the OS
 *      4) propagates RCM operations from mounted resources to the consumers
 *         of files within the mounted filesystems
 */

#include <stdio.h>
#include <assert.h>
#include <string.h>
#include <synch.h>
#include <libintl.h>
#include <errno.h>
#include <sys/mnttab.h>
#include <sys/param.h>
#include <sys/stat.h>
#include <sys/utssys.h>
#include <unistd.h>
#include <limits.h>

#include "rcm_module.h"

/* Definitions */

#define HASH_DEFAULT            4
#define HASH_THRESHOLD          256

#define OPT_IGNORE              "ignore"

#define MSG_HDR_STD             gettext("mounted filesystem")
#define MSG_HDR_STD_MULTI       gettext("mounted filesystems")
#define MSG_HDR_CRIT            gettext("cannot suspend filesystem")
#define MSG_HDR_CRIT_MULTI      gettext("cannot suspend filesystems")
#define MSG_SEPARATOR           gettext(", ")
#define MSG_FAIL_USAGE          gettext("failed to construct usage string.")
#define MSG_FAIL_DEPENDENTS     gettext("failed while calling dependents.")
#define MSG_FAIL_REMOVE         gettext("filesystems cannot be removed.")
#define MSG_FAIL_INTERNAL       gettext("internal processing failure.")

typedef struct hashentry {
        int n_mounts;
        char *special;
        char *fstype;
        char **mountps;
        struct hashentry *next;
} hashentry_t;

typedef struct {
        time_t timestamp;
        uint32_t hash_size;
        hashentry_t **mounts;
} cache_t;

/* Forward Declarations */

/* module interface routines */
static int mnt_register(rcm_handle_t *);
static int mnt_unregister(rcm_handle_t *);
static int mnt_getinfo(rcm_handle_t *, char *, id_t, uint_t, char **, char **,
    nvlist_t *, rcm_info_t **);
static int mnt_suspend(rcm_handle_t *, char *, id_t, timespec_t *,
    uint_t, char **, rcm_info_t **);
static int mnt_resume(rcm_handle_t *, char *, id_t, uint_t, char **,
    rcm_info_t **);
static int mnt_offline(rcm_handle_t *, char *, id_t, uint_t, char **,
    rcm_info_t **);
static int mnt_online(rcm_handle_t *, char *, id_t, uint_t, char **,
    rcm_info_t **);
static int mnt_remove(rcm_handle_t *, char *, id_t, uint_t, char **,
    rcm_info_t **);

/* cache functions */
static cache_t *cache_create();
static int cache_insert(cache_t *, struct mnttab *);
static int cache_sync(rcm_handle_t *, cache_t **);
static hashentry_t *cache_lookup(cache_t *, char *);
static void free_cache(cache_t **);
static void free_entry(hashentry_t **);
static void free_list(char **);

/* miscellaneous functions */
static uint32_t hash(uint32_t, char *);
static void register_rsrc(rcm_handle_t *, char *);
static void unregister_rsrc(rcm_handle_t *, char *);
static char *create_message(char *, char *, char **);
static int detect_critical_failure(char **, uint_t, char **);
static int is_critical(char *);
static int use_cache(char *, char **, char ***);
static void prune_dependents(char **, char *);
static char **create_dependents(hashentry_t *);

/* Module-Private data */

static struct rcm_mod_ops mnt_ops =
{
        RCM_MOD_OPS_VERSION,
        mnt_register,
        mnt_unregister,
        mnt_getinfo,
        mnt_suspend,
        mnt_resume,
        mnt_offline,
        mnt_online,
        mnt_remove
};

static cache_t *mnt_cache;
static mutex_t cache_lock;

/* Module Interface Routines */

/*
 * rcm_mod_init()
 *
 *      Called when module is loaded.  Returns the ops vector.
 */
struct rcm_mod_ops *
rcm_mod_init()
{
        return (&mnt_ops);
}

/*
 * rcm_mod_info()
 *
 *      Returns a string identifying this module.
 */
const char *
rcm_mod_info()
{
        return ("File system module 1.9");
}

/*
 * rcm_mod_fini()
 *
 *      Called when module is unloaded.  Frees up all used memory.
 *
 *      Locking: the cache is locked for the duration of this function.
 */
int
rcm_mod_fini()
{
        (void) mutex_lock(&cache_lock);
        free_cache(&mnt_cache);
        (void) mutex_unlock(&cache_lock);

        return (RCM_SUCCESS);
}

/*
 * mnt_register()
 *
 *      Called to synchronize the module's registrations.  Results in the
 *      construction of a new cache, destruction of any old cache data,
 *      and a full synchronization of the module's registrations.
 *
 *      Locking: the cache is locked for the duration of this function.
 */
int
mnt_register(rcm_handle_t *hd)
{
        assert(hd != NULL);

        rcm_log_message(RCM_TRACE1, "FILESYS: register()\n");

        (void) mutex_lock(&cache_lock);

        /* cache_sync() does all of the necessary work */
        if (cache_sync(hd, &mnt_cache) < 0) {
                rcm_log_message(RCM_ERROR,
                    "FILESYS: failed to synchronize cache (%s).\n",
                    strerror(errno));
                (void) mutex_unlock(&cache_lock);
                return (RCM_FAILURE);
        }

        (void) mutex_unlock(&cache_lock);

        return (RCM_SUCCESS);
}

/*
 * mnt_unregister()
 *
 *      Manually walk through the cache, unregistering all the special
 *      files and mount points.
 *
 *      Locking: the cache is locked throughout the execution of this
 *      routine because it reads and modifies cache links continuously.
 */
int
mnt_unregister(rcm_handle_t *hd)
{
        uint32_t index;
        hashentry_t *entry;

        assert(hd != NULL);

        rcm_log_message(RCM_TRACE1, "FILESYS: unregister()\n");

        (void) mutex_lock(&cache_lock);

        /* Unregister everything in the cache */
        if (mnt_cache) {
                for (index = 0; index < mnt_cache->hash_size; index++) {
                        for (entry = mnt_cache->mounts[index]; entry != NULL;
                            entry = entry->next) {
                                unregister_rsrc(hd, entry->special);
                        }
                }
        }

        /* Destroy the cache */
        free_cache(&mnt_cache);

        (void) mutex_unlock(&cache_lock);

        return (RCM_SUCCESS);
}

/*
 * mnt_offline()
 *
 *      Filesystem resources cannot be offlined. They can however be retired
 *      if they don't provide a critical service. The offline entry point
 *      checks if this is a retire operation and if it is and the filesystem
 *      doesn't provide a critical service, the entry point returns success
 *      For all other cases, failure is returned.
 *      Since no real action is taken, QUERY or not doesn't matter.
 */
int
mnt_offline(rcm_handle_t *hd, char *rsrc, id_t id, uint_t flags,
    char **errorp, rcm_info_t **dependent_info)
{
        char **dependents;
        hashentry_t *entry;
        int retval;
        int i;

        assert(hd != NULL);
        assert(rsrc != NULL);
        assert(id == (id_t)0);
        assert(errorp != NULL);

        *errorp = NULL;

        rcm_log_message(RCM_TRACE1, "FILESYS: offline(%s)\n", rsrc);

        /* Retrieve necessary info from the cache */
        if (use_cache(rsrc, errorp, &dependents) < 0) {
                if (flags & RCM_RETIRE_REQUEST)
                        return (RCM_NO_CONSTRAINT);
                else
                        return (RCM_FAILURE);
        }

        if (flags & RCM_RETIRE_REQUEST) {
                (void) mutex_lock(&cache_lock);
                if ((entry = cache_lookup(mnt_cache, rsrc)) == NULL) {
                        rcm_log_message(RCM_ERROR, "FILESYS: "
                            "failed to look up \"%s\" in cache (%s).\n",
                            rsrc, strerror(errno));
                        (void) mutex_unlock(&cache_lock);
                        retval = RCM_NO_CONSTRAINT;
                        goto out;
                }

                if (strcmp(entry->fstype, "zfs") == 0) {
                        retval = RCM_NO_CONSTRAINT;
                        rcm_log_message(RCM_TRACE1,
                            "FILESYS: zfs: NO_CONSTRAINT: %s\n", rsrc);
                } else {
                        retval = RCM_SUCCESS;
                        for (i = 0; dependents[i] != NULL; i++) {
                                if (is_critical(dependents[i])) {
                                        retval = RCM_FAILURE;
                                        rcm_log_message(RCM_TRACE1, "FILESYS: "
                                            "CRITICAL %s\n", rsrc);
                                        break;
                                }
                        }
                }
                (void) mutex_unlock(&cache_lock);
                goto out;
        }

        retval = RCM_FAILURE;

        /* Convert the gathered dependents into an error message */
        *errorp = create_message(MSG_HDR_STD, MSG_HDR_STD_MULTI, dependents);
        if (*errorp == NULL) {
                rcm_log_message(RCM_ERROR,
                    "FILESYS: failed to construct offline message (%s).\n",
                    strerror(errno));
        }

out:
        free_list(dependents);
        return (retval);
}

/*
 * mnt_online()
 *
 *      Filesystem resources aren't offlined, so there's really nothing to do
 *      here.
 */
int
mnt_online(rcm_handle_t *hd, char *rsrc, id_t id, uint_t flag, char **errorp,
    rcm_info_t **dependent_reason)
{
        assert(hd != NULL);
        assert(rsrc != NULL);
        assert(id == (id_t)0);
        assert(errorp != NULL);

        rcm_log_message(RCM_TRACE1, "FILESYS: online(%s)\n", rsrc);

        return (RCM_SUCCESS);
}

/*
 * mnt_getinfo()
 *
 *      Report how a given resource is in use by this module.  And also
 *      possibly include dependent consumers of the mounted filesystems.
 */
int
mnt_getinfo(rcm_handle_t *hd, char *rsrc, id_t id, uint_t flag, char **usagep,
    char **errorp, nvlist_t *props, rcm_info_t **depend_info)
{
        int rv = RCM_SUCCESS;
        char **dependents;

        assert(hd != NULL);
        assert(rsrc != NULL);
        assert(id == (id_t)0);
        assert(usagep != NULL);
        assert(errorp != NULL);
        assert(props != NULL);

        rcm_log_message(RCM_TRACE1, "FILESYS: getinfo(%s)\n", rsrc);

        /* Retrieve necessary info from the cache */
        if (use_cache(rsrc, errorp, &dependents) < 0)
                return (RCM_FAILURE);

        /* Convert the gathered dependents into a usage message */
        *usagep = create_message(MSG_HDR_STD, MSG_HDR_STD_MULTI, dependents);
        if (*usagep == NULL) {
                rcm_log_message(RCM_ERROR,
                    "FILESYS: failed to construct usage message (%s).\n",
                    strerror(errno));
                *errorp = strdup(MSG_FAIL_USAGE);
                free_list(dependents);
                return (RCM_FAILURE);
        }

        /* Recurse on dependents if necessary */
        if ((flag & RCM_INCLUDE_DEPENDENT) && (dependents != NULL)) {
                prune_dependents(dependents, rsrc);
                if (dependents[0] != NULL) {
                        if ((rv = rcm_get_info_list(hd, dependents, flag,
                            depend_info)) != RCM_SUCCESS) {
                                *errorp = strdup(MSG_FAIL_DEPENDENTS);
                        }
                }
        }

        /* Free up info retrieved from the cache */
        free_list(dependents);

        return (rv);
}

/*
 * mnt_suspend()
 *
 *      Notify all dependents that the resource is being suspended.
 *      Since no real action is taken, QUERY or not doesn't matter.
 */
int
mnt_suspend(rcm_handle_t *hd, char *rsrc, id_t id, timespec_t *interval,
    uint_t flag, char **errorp, rcm_info_t **depend_info)
{
        int rv = RCM_SUCCESS;
        char **dependents;

        assert(hd != NULL);
        assert(rsrc != NULL);
        assert(id == (id_t)0);
        assert(interval != NULL);
        assert(errorp != NULL);

        rcm_log_message(RCM_TRACE1, "FILESYS: suspend(%s)\n", rsrc);

        /* Retrieve necessary info from the cache */
        if (use_cache(rsrc, errorp, &dependents) < 0)
                return (RCM_FAILURE);

        /* Unforced suspensions fail if any of the dependents are critical */
        if (detect_critical_failure(errorp, flag, dependents)) {
                free_list(dependents);
                return (RCM_FAILURE);
        }

        /* Recurse on dependents if necessary */
        if ((flag & RCM_INCLUDE_DEPENDENT) && (dependents != NULL)) {
                prune_dependents(dependents, rsrc);
                if (dependents[0] != NULL)
                        if ((rv = rcm_request_suspend_list(hd, dependents, flag,
                            interval, depend_info)) != RCM_SUCCESS) {
                                *errorp = strdup(MSG_FAIL_DEPENDENTS);
                        }
        }
        free_list(dependents);

        return (rv);
}

/*
 * mnt_resume()
 *
 *      Resume all the dependents of a suspended filesystem.
 */
int
mnt_resume(rcm_handle_t *hd, char *rsrc, id_t id, uint_t flag, char **errorp,
    rcm_info_t **depend_info)
{
        int rv = RCM_SUCCESS;
        char **dependents;

        assert(hd != NULL);
        assert(rsrc != NULL);
        assert(id == (id_t)0);
        assert(errorp != NULL);

        rcm_log_message(RCM_TRACE1, "FILESYS: resume(%s)\n", rsrc);

        /* Retrieve necessary info from the cache */
        if (use_cache(rsrc, errorp, &dependents) < 0)
                return (RCM_FAILURE);

        /* Recurse on dependents if necessary */
        if ((flag & RCM_INCLUDE_DEPENDENT) && (dependents != NULL)) {
                prune_dependents(dependents, rsrc);
                if (dependents[0] != NULL) {
                        if ((rv = rcm_notify_resume_list(hd, dependents, flag,
                            depend_info)) != RCM_SUCCESS) {
                                *errorp = strdup(MSG_FAIL_DEPENDENTS);
                        }
                }
        }
        free_list(dependents);

        return (rv);
}

static int
get_spec(char *line, char *spec, size_t ssz)
{
        char    *cp;
        char    *start;

        if (strlcpy(spec, line, ssz) >= ssz) {
                rcm_log_message(RCM_ERROR, "FILESYS: get_spec() failed: "
                    "line: %s\n", line);
                return (-1);
        }

        cp = spec;
        while (*cp == ' ' || *cp == '\t')
                cp++;

        if (*cp == '#')
                return (-1);

        start = cp;

        while (*cp != ' ' && *cp != '\t' && *cp != '\0')
                cp++;
        *cp = '\0';

        (void) memmove(spec, start, strlen(start) + 1);

        return (0);
}

static int
path_match(char *rsrc, char *spec)
{
        char r[PATH_MAX];
        char s[PATH_MAX];
        size_t len;

        if (realpath(rsrc, r) == NULL)
                goto error;

        if (realpath(spec, s) == NULL)
                goto error;

        len = strlen("/devices/");

        if (strncmp(r, "/devices/", len) != 0) {
                errno = ENXIO;
                goto error;
        }

        if (strncmp(s, "/devices/", len) != 0) {
                errno = ENXIO;
                goto error;
        }

        len = strlen(r);
        if (strncmp(r, s, len) == 0 && (s[len] == '\0' || s[len] == ':'))
                return (0);
        else
                return (1);

error:
        rcm_log_message(RCM_DEBUG, "FILESYS: path_match() failed "
            "rsrc=%s spec=%s: %s\n", rsrc, spec, strerror(errno));
        return (-1);
}

#define VFSTAB          "/etc/vfstab"
#define RETIRED_PREFIX  "## RETIRED ##"

static int
disable_vfstab_entry(char *rsrc)
{
        FILE    *vfp;
        FILE    *tfp;
        int     retval;
        int     update;
        char    tmp[PATH_MAX];
        char    line[MNT_LINE_MAX + 1];

        vfp = fopen(VFSTAB, "r");
        if (vfp == NULL) {
                rcm_log_message(RCM_ERROR, "FILESYS: failed to open /etc/vfstab"
                    " for reading: %s\n", strerror(errno));
                return (RCM_FAILURE);
        }

        (void) snprintf(tmp, sizeof (tmp), "/etc/vfstab.retire.%lu", getpid());

        tfp = fopen(tmp, "w");
        if (tfp == NULL) {
                rcm_log_message(RCM_ERROR, "FILESYS: failed to open "
                    "/etc/vfstab.retire for writing: %s\n", strerror(errno));
                (void) fclose(vfp);
                return (RCM_FAILURE);
        }

        retval = RCM_SUCCESS;
        update = 0;
        while (fgets(line, sizeof (line), vfp)) {

                char    spec[MNT_LINE_MAX + 1];
                char    newline[MNT_LINE_MAX + 1];
                char    *l;

                if (get_spec(line, spec, sizeof (spec)) == -1) {
                        l = line;
                        goto foot;
                }

                if (path_match(rsrc, spec) != 0) {
                        l = line;
                        goto foot;
                }

                update = 1;

                /* Paths match. Disable this entry */
                (void) snprintf(newline, sizeof (newline), "%s %s",
                    RETIRED_PREFIX, line);

                rcm_log_message(RCM_TRACE1, "FILESYS: disabling line\n\t%s\n",
                    line);

                l = newline;
foot:
                if (fputs(l, tfp) == EOF) {
                        rcm_log_message(RCM_ERROR, "FILESYS: failed to write "
                            "new vfstab: %s\n", strerror(errno));
                        update = 0;
                        retval = RCM_FAILURE;
                        break;
                }
        }

        if (vfp)
                (void) fclose(vfp);
        if (tfp)
                (void) fclose(tfp);

        if (update) {
                if (rename(tmp, VFSTAB) != 0) {
                        rcm_log_message(RCM_ERROR, "FILESYS: vfstab rename "
                            "failed: %s\n", strerror(errno));
                        retval = RCM_FAILURE;
                }
        }

        (void) unlink(tmp);

        return (retval);
}

/*
 * mnt_remove()
 *
 *      Remove will only be called in the retire case i.e. if RCM_RETIRE_NOTIFY
 *      flag is set.
 *
 *      If the flag is not set, then return failure and log the mistake if a
 *      remove is ever received for a mounted filesystem resource.
 */
int
mnt_remove(rcm_handle_t *hd, char *rsrc, id_t id, uint_t flag, char **errorp,
    rcm_info_t **depend_info)
{
        assert(hd != NULL);
        assert(rsrc != NULL);
        assert(id == (id_t)0);
        assert(errorp != NULL);

        rcm_log_message(RCM_TRACE1, "FILESYS: remove(%s)\n", rsrc);

        if (!(flag & RCM_RETIRE_NOTIFY)) {
                /* Log the mistake */
                rcm_log_message(RCM_ERROR, "FILESYS: invalid remove of "
                    "\"%s\"\n", rsrc);
                *errorp = strdup(MSG_FAIL_REMOVE);
                return (RCM_FAILURE);
        }

        return (disable_vfstab_entry(rsrc));
}

/*
 * Cache management routines
 */

/*
 * cache_create()
 *
 *      This routine constructs a new cache of the current mnttab file.
 *
 *      Locking: the cache must be locked prior to calling this function.
 *
 *      Return Values: NULL with errno set on failure, new cache point on
 *      success.
 */
static cache_t *
cache_create()
{
        FILE *fp;
        cache_t *cache;
        int i;
        uint32_t size;
        struct stat st;
        struct mnttab mt;

        /*
         * To keep the hash table relatively sparse, default values are
         * used for smaller mnttab files and these values are scaled up
         * as a fraction of the total mnttab file size for larger ones.
         */
        if (stat(MNTTAB, &st) < 0) {
                rcm_log_message(RCM_ERROR,
                    "FILESYS: failed to stat \"%s\" (%s).\n", MNTTAB,
                    strerror(errno));
                errno = EBADF;
                return (NULL);
        }
        if (st.st_size > HASH_THRESHOLD) {
                size = st.st_size / HASH_THRESHOLD;
                for (i = 0; size > 1; i++, size >>= 1);
                for (; i > -1; i--, size <<= 1);
        } else {
                size = HASH_DEFAULT;
        }

        /* Allocate a new empty cache */
        if ((cache = (cache_t *)calloc(1, sizeof (cache_t))) == NULL) {
                rcm_log_message(RCM_ERROR,
                    "FILESYS: failed to allocate cache (%s).\n",
                    strerror(errno));
                errno = ENOMEM;
                return (NULL);
        }
        cache->hash_size = size;
        cache->timestamp = st.st_mtime;

        /* Allocate an empty hash table for the registered special devices */
        cache->mounts = (hashentry_t **)calloc(size, sizeof (hashentry_t *));
        if (cache->mounts == NULL) {
                rcm_log_message(RCM_ERROR,
                    "FILESYS: failed to allocate mount table (%s).\n",
                    strerror(errno));
                free_cache(&cache);
                errno = ENOMEM;
                return (NULL);
        }

        /* Open the mnttab file */
        if ((fp = fopen(MNTTAB, "r")) == NULL) {
                rcm_log_message(RCM_ERROR,
                    "FILESYS: failed to open \"%s\" (%s).\n", MNTTAB,
                    strerror(errno));
                free_cache(&cache);
                errno = EIO;
                return (NULL);
        }

        /* Insert each mnttab entry into the cache */
        while (getmntent(fp, &mt) == 0) {

                /* Well, not each entry... some are meant to be ignored */
                if ((mt.mnt_mntopts != NULL) &&
                    (hasmntopt(&mt, OPT_IGNORE) != NULL))
                        continue;

                if (cache_insert(cache, &mt) < 0) {
                        rcm_log_message(RCM_ERROR,
                            "FILESYS: cache insertion failure (%s).\n",
                            strerror(errno));
                        free_cache(&cache);
                        (void) fclose(fp);
                        errno = EFAULT;
                        return (NULL);
                }
        }

        /* Close the mnttab file */
        (void) fclose(fp);

        return (cache);
}

/*
 * free_cache()
 *
 *      Free up all the memory associated with a cache.
 *
 *      Locking: the cache must be locked before calling this function.
 */
static void
free_cache(cache_t **cachep)
{
        uint32_t index;
        hashentry_t *entry;
        hashentry_t *entry_tmp;

        /* Do nothing with empty caches */
        if ((cachep == NULL) || (*cachep == NULL))
                return;

        if ((*cachep)->mounts) {
                /* Walk through the hashtable, emptying it */
                for (index = 0; index < (*cachep)->hash_size; index++) {
                        entry = (*cachep)->mounts[index];
                        while (entry) {
                                entry_tmp = entry->next;
                                free_entry(&entry);
                                entry = entry_tmp;
                        }
                }
                free((*cachep)->mounts);
        }

        free(*cachep);
        *cachep = NULL;
}

/*
 * free_entry()
 *
 *      Free up memory associated with a hashtable entry.
 *
 *      Locking: the cache must be locked before calling this function.
 */
static void
free_entry(hashentry_t **entryp)
{
        if (entryp) {
                if (*entryp) {
                        if ((*entryp)->special)
                                free((*entryp)->special);
                        if ((*entryp)->fstype)
                                free((*entryp)->fstype);
                        free_list((*entryp)->mountps);
                        free(*entryp);
                }
                *entryp = NULL;
        }
}

/*
 * free_list()
 *
 *      Free up memory associated with a null terminated list of names.
 */
static void
free_list(char **list)
{
        int i;

        if (list) {
                for (i = 0; list[i] != NULL; i++)
                        free(list[i]);
                free(list);
        }
}

/*
 * cache_sync()
 *
 *      Resynchronize the mnttab cache with the mnttab file.
 *
 *      Locking: the cache must be locked before calling this function.
 *
 *      Return Values: -1 with errno set on failure, 0 on success.
 */
static int
cache_sync(rcm_handle_t *hd, cache_t **cachep)
{
        uint32_t index;
        cache_t *new_cache;
        cache_t *old_cache;
        hashentry_t *entry;
        struct stat st;

        /* Only accept valid arguments */
        if ((hd == NULL) || (cachep == NULL)) {
                rcm_log_message(RCM_ERROR,
                    "FILESYS: invalid arguments to cache_sync().\n");
                errno = EINVAL;
                return (-1);
        }

        /* Do nothing if there's already an up-to-date cache */
        old_cache = *cachep;
        if (old_cache) {
                if (stat(MNTTAB, &st) == 0) {
                        if (old_cache->timestamp >= st.st_mtime) {
                                return (0);
                        }
                } else {
                        rcm_log_message(RCM_WARNING,
                            "FILESYS: failed to stat \"%s\", cache is stale "
                            "(%s).\n", MNTTAB, strerror(errno));
                        errno = EIO;
                        return (-1);
                }
        }

        /* Create a new cache based on the new mnttab file.  */
        if ((new_cache = cache_create()) == NULL) {
                rcm_log_message(RCM_WARNING,
                    "FILESYS: failed creating cache, cache is stale (%s).\n",
                    strerror(errno));
                errno = EIO;
                return (-1);
        }

        /* Register any specials found in the new cache but not the old one */
        for (index = 0; index < new_cache->hash_size; index++) {
                for (entry = new_cache->mounts[index]; entry != NULL;
                    entry = entry->next) {
                        if (cache_lookup(old_cache, entry->special) == NULL) {
                                register_rsrc(hd, entry->special);
                        }
                }
        }

        /* Pass the new cache pointer to the calling function */
        *cachep = new_cache;

        /* If there wasn't an old cache, return successfully now */
        if (old_cache == NULL)
                return (0);

        /*
         * If there was an old cache, then unregister whatever specials it
         * contains that aren't in the new cache.  And then destroy the old
         * cache.
         */
        for (index = 0; index < old_cache->hash_size; index++) {
                for (entry = old_cache->mounts[index]; entry != NULL;
                    entry = entry->next) {
                        if (cache_lookup(new_cache, entry->special) == NULL) {
                                unregister_rsrc(hd, entry->special);
                        }
                }
        }
        free_cache(&old_cache);

        return (0);
}

/*
 * cache_insert()
 *
 *      Given a cache and a mnttab entry, this routine inserts that entry in
 *      the cache.  The mnttab entry's special device and filesystem type
 *      is added to the 'mounts' hashtable of the cache, and the entry's
 *      mountp value is added to the list of associated mountpoints for the
 *      corresponding hashtable entry.
 *
 *      Locking: the cache must be locked before calling this function.
 *
 *      Return Values: -1 with errno set on failure, 0 on success.
 */
static int
cache_insert(cache_t *cache, struct mnttab *mt)
{
        uint32_t index;
        hashentry_t *entry;
        char **mountps;

        /* Only accept valid arguments */
        if ((cache == NULL) ||
            (cache->mounts == NULL) ||
            (mt == NULL) ||
            (mt->mnt_special == NULL) ||
            (mt->mnt_mountp == NULL) ||
            (mt->mnt_fstype == NULL)) {
                errno = EINVAL;
                return (-1);
        }

        /*
         * Disregard any non-loopback mounts whose special device names
         * don't begin with "/dev".
         */
        if ((strncmp(mt->mnt_special, "/dev", strlen("/dev")) != 0) &&
            (strcmp(mt->mnt_fstype, "lofs") != 0))
                return (0);

        /*
         * Find the special device's entry in the mounts hashtable, allocating
         * a new entry if necessary.
         */
        index = hash(cache->hash_size, mt->mnt_special);
        for (entry = cache->mounts[index]; entry != NULL; entry = entry->next) {
                if (strcmp(entry->special, mt->mnt_special) == 0)
                        break;
        }
        if (entry == NULL) {
                entry = (hashentry_t *)calloc(1, sizeof (hashentry_t));
                if ((entry == NULL) ||
                    ((entry->special = strdup(mt->mnt_special)) == NULL) ||
                    ((entry->fstype = strdup(mt->mnt_fstype)) == NULL)) {
                        rcm_log_message(RCM_ERROR,
                            "FILESYS: failed to allocate special device name "
                            "or filesystem type: (%s).\n", strerror(errno));
                        free_entry(&entry);
                        errno = ENOMEM;
                        return (-1);
                }
                entry->next = cache->mounts[index];
                cache->mounts[index] = entry;
        }

        /*
         * Keep entries in the list of mounts unique, so exit early if the
         * mount is already in the list.
         */
        for (index = 0; index < entry->n_mounts; index++) {
                if (strcmp(entry->mountps[index], mt->mnt_mountp) == 0)
                        return (0);
        }

        /*
         * Add this mountpoint to the list of mounts associated with the
         * special device.
         */
        mountps = (char **)realloc(entry->mountps,
            (entry->n_mounts + 2) * sizeof (char *));
        if ((mountps == NULL) ||
            ((mountps[entry->n_mounts] = strdup(mt->mnt_mountp)) == NULL)) {
                rcm_log_message(RCM_ERROR,
                    "FILESYS: failed to allocate mountpoint name (%s).\n",
                    strerror(errno));
                if (entry->n_mounts == 0) {
                        cache->mounts[index] = entry->next;
                        free_entry(&entry);
                }
                errno = ENOMEM;
                return (-1);
        }
        mountps[entry->n_mounts + 1] = NULL;
        entry->n_mounts++;
        entry->mountps = mountps;

        return (0);
}

/*
 * cache_lookup()
 *
 *      Searches the cached table of mounts for a special device entry.
 *
 *      Locking: the cache must be locked before calling this function.
 *
 *      Return Value: NULL with errno set if failure, pointer to existing
 *      cache entry when successful.
 */
static hashentry_t *
cache_lookup(cache_t *cache, char *rsrc)
{
        uint32_t index;
        hashentry_t *entry;

        /* Only accept valid arguments */
        if ((cache == NULL) || (cache->mounts == NULL) || (rsrc == NULL)) {
                errno = EINVAL;
                return (NULL);
        }

        /* Search the cached mounts table for the resource's entry */
        index = hash(cache->hash_size, rsrc);
        if (cache->mounts[index]) {
                for (entry = cache->mounts[index]; entry != NULL;
                    entry = entry->next) {
                        if (strcmp(entry->special, rsrc) == 0)
                                return (entry);
                }
        }

        errno = ENOENT;
        return (NULL);
}

/*
 * Miscellaneous Functions
 */

/*
 * hash()
 *
 *      A naive hashing function that converts a string 's' to an index in a
 *      hash table of size 'h'.  It seems to spread entries around well enough.
 */
static uint32_t
hash(uint32_t h, char *s)
{
        uint32_t sum = 0;
        unsigned char *byte;

        if ((byte = (unsigned char *)s) != NULL) {
                while (*byte) {
                        sum += 0x3F & (uint32_t)*byte;
                        byte++;
                }
        }

        return (sum % h);
}

/*
 * register_rsrc()
 *
 *      Registers for any given resource, unless it's "/".
 */
static void
register_rsrc(rcm_handle_t *hd, char *rsrc)
{
        /* Only accept valid arguments */
        if ((hd == NULL) || (rsrc == NULL))
                return;

        /*
         * Register any resource other than "/" or "/devices"
         */
        if ((strcmp(rsrc, "/") != 0) && (strcmp(rsrc, "/devices") != 0)) {
                rcm_log_message(RCM_DEBUG, "FILESYS: registering %s\n", rsrc);
                if (rcm_register_interest(hd, rsrc, 0, NULL) != RCM_SUCCESS) {
                        rcm_log_message(RCM_WARNING,
                            "FILESYS: failed to register %s\n", rsrc);
                }
        }

}

/*
 * unregister_rsrc()
 *
 *      Unregister a resource.  This does a little filtering since we know
 *      "/" can't be registered, so we never bother unregistering for it.
 */
static void
unregister_rsrc(rcm_handle_t *hd, char *rsrc)
{
        assert(hd != NULL);
        assert(rsrc != NULL);

        /* Unregister any resource other than "/" */
        if (strcmp(rsrc, "/") != 0) {
                rcm_log_message(RCM_DEBUG, "FILESYS: unregistering %s\n", rsrc);
                (void) rcm_unregister_interest(hd, rsrc, 0);
        }
}

/*
 * create_message()
 *
 *      Given some header strings and a list of dependent names, this
 *      constructs a single string.  If there's only one dependent, the
 *      string consists of the first header and the only dependent appended
 *      to the end of the string enclosed in quotemarks.  If there are
 *      multiple dependents, then the string uses the second header and the
 *      full list of dependents is appended at the end as a comma separated
 *      list of names enclosed in quotemarks.
 */
static char *
create_message(char *header, char *header_multi, char **dependents)
{
        int i;
        size_t len;
        int ndependents;
        char *msg_buf;
        char *msg_header;
        char *separator = MSG_SEPARATOR;

        assert(header != NULL);
        assert(header_multi != NULL);
        assert(dependents != NULL);

        /* Count the number of dependents */
        for (ndependents = 0; dependents[ndependents] != NULL; ndependents++);

        /* If there are no dependents, fail */
        if (ndependents == 0) {
                errno = ENOENT;
                return (NULL);
        }

        /* Pick the appropriate header to use based on amount of dependents */
        if (ndependents == 1) {
                msg_header = header;
        } else {
                msg_header = header_multi;
        }

        /* Compute the size required for the message buffer */
        len = strlen(msg_header) + 2;   /* +2 for the space and a NULL */
        for (i = 0; dependents[i] != NULL; i++)
                len += strlen(dependents[i]) + 2;       /* +2 for quotemarks */
        len += strlen(separator) * (ndependents - 1);

        /* Allocate the message buffer */
        if ((msg_buf = (char *)calloc(len, sizeof (char))) == NULL) {
                rcm_log_message(RCM_ERROR,
                    "FILESYS: failed to allocate message buffer (%s).\n",
                    strerror(errno));
                errno = ENOMEM;
                return (NULL);
        }

        /* Fill in the message buffer */
        (void) snprintf(msg_buf, len, "%s ", msg_header);
        for (i = 0; dependents[i] != NULL; i++) {
                (void) strlcat(msg_buf, "\"", len);
                (void) strlcat(msg_buf, dependents[i], len);
                (void) strlcat(msg_buf, "\"", len);
                if ((i + 1) < ndependents)
                        (void) strlcat(msg_buf, separator, len);
        }

        return (msg_buf);
}

/*
 * create_dependents()
 *
 *      Creates a copy of the list of dependent mounts associated with a
 *      given hashtable entry from the cache.
 *
 *      Return Values: NULL with errno set on failure, the resulting list of
 *      dependent resources when successful.
 */
static char **
create_dependents(hashentry_t *entry)
{
        int i;
        char **dependents;

        if (entry == NULL) {
                errno = EINVAL;
                return (NULL);
        }

        if (entry->n_mounts == 0) {
                errno = ENOENT;
                return (NULL);
        }

        /* Allocate space for the full dependency list */
        dependents = (char **)calloc(entry->n_mounts + 1, sizeof (char *));
        if (dependents == NULL) {
                rcm_log_message(RCM_ERROR,
                    "FILESYS: failed to allocate dependents (%s).\n",
                    strerror(errno));
                errno = ENOMEM;
                return (NULL);
        }

        /* Copy all the dependent names into the new list of dependents */
        for (i = 0; i < entry->n_mounts; i++) {
                if ((dependents[i] = strdup(entry->mountps[i])) == NULL) {
                        rcm_log_message(RCM_ERROR,
                            "FILESYS: failed to allocate dependent \"%s\" "
                            "(%s).\n", entry->mountps[i], strerror(errno));
                        free_list(dependents);
                        errno = ENOMEM;
                        return (NULL);
                }
        }

        return (dependents);
}

/*
 * detect_critical_failure()
 *
 *      Given a list of dependents, a place to store an error message, and
 *      the flags associated with an operation, this function detects whether
 *      or not the operation should fail due to the presence of any critical
 *      filesystem resources.  When a failure is detected, an appropriate
 *      error message is constructed and passed back to the caller.  This is
 *      called during a suspend request operation.
 *
 *      Return Values: 0 when a critical resource failure shouldn't prevent
 *      the operation, and 1 when such a failure condition does exist.
 */
static int
detect_critical_failure(char **errorp, uint_t flags, char **dependents)
{
        int i;
        int n_critical;
        char *tmp;

        /* Do nothing if the operation is forced or there are no dependents */
        if ((errorp == NULL) || (flags & RCM_FORCE) || (dependents == NULL))
                return (0);

        /*
         * Count how many of the dependents are critical, and shift the
         * critical resources to the head of the list.
         */
        if (dependents) {
                for (i = 0, n_critical = 0; dependents[i] != NULL; i++) {
                        if (is_critical(dependents[i])) {
                                if (n_critical != i) {
                                        tmp = dependents[n_critical];
                                        dependents[n_critical] = dependents[i];
                                        dependents[i] = tmp;
                                }
                                n_critical++;
                        }
                }
        }

        /* If no criticals were found, do nothing and return */
        if (n_critical == 0)
                return (0);

        /*
         * Criticals were found.  Prune the list appropriately and construct
         * an error message.
         */

        /* Prune non-criticals out of the list */
        for (i = n_critical; dependents[i] != NULL; i++) {
                free(dependents[i]);
                dependents[i] = NULL;
        }

        /* Construct the critical resource error message */
        *errorp = create_message(MSG_HDR_CRIT, MSG_HDR_CRIT_MULTI, dependents);

        return (1);
}

/*
 * is_critical()
 *
 *      Test a resource to determine if it's critical to the system and thus
 *      cannot be suspended.
 *
 *      Return Values: 1 if the named resource is critical, 0 if not.
 */
static int
is_critical(char *rsrc)
{
        assert(rsrc != NULL);

        if ((strcmp(rsrc, "/") == 0) ||
            (strcmp(rsrc, "/usr") == 0) ||
            (strcmp(rsrc, "/lib") == 0) ||
            (strcmp(rsrc, "/usr/lib") == 0) ||
            (strcmp(rsrc, "/bin") == 0) ||
            (strcmp(rsrc, "/usr/bin") == 0) ||
            (strcmp(rsrc, "/tmp") == 0) ||
            (strcmp(rsrc, "/var") == 0) ||
            (strcmp(rsrc, "/var/run") == 0) ||
            (strcmp(rsrc, "/etc") == 0) ||
            (strcmp(rsrc, "/etc/mnttab") == 0) ||
            (strcmp(rsrc, "/platform") == 0) ||
            (strcmp(rsrc, "/usr/platform") == 0) ||
            (strcmp(rsrc, "/sbin") == 0) ||
            (strcmp(rsrc, "/usr/sbin") == 0))
                return (1);

        return (0);
}


/*
 * use_cache()
 *
 *      This routine handles all the tasks necessary to lookup a resource
 *      in the cache and extract a separate list of dependents for that
 *      entry.  If an error occurs while doing this, an appropriate error
 *      message is passed back to the caller.
 *
 *      Locking: the cache is locked for the whole duration of this function.
 */
static int
use_cache(char *rsrc, char **errorp, char ***dependentsp)
{
        hashentry_t *entry;

        (void) mutex_lock(&cache_lock);
        if ((entry = cache_lookup(mnt_cache, rsrc)) == NULL) {
                rcm_log_message(RCM_ERROR,
                    "FILESYS: failed looking up \"%s\" in cache (%s).\n",
                    rsrc, strerror(errno));
                *errorp = strdup(MSG_FAIL_INTERNAL);
                (void) mutex_unlock(&cache_lock);
                return (-1);
        }
        *dependentsp = create_dependents(entry);
        (void) mutex_unlock(&cache_lock);

        return (0);
}

/*
 * prune_dependents()
 *
 *      Before calling back into RCM with a list of dependents, the list
 *      must be cleaned up a little.  To avoid infinite recursion, "/" and
 *      the named resource must be pruned out of the list.
 */
static void
prune_dependents(char **dependents, char *rsrc)
{
        int i;
        int n;

        if (dependents) {

                /* Set 'n' to the total length of the list */
                for (n = 0; dependents[n] != NULL; n++);

                /*
                 * Move offending dependents to the tail of the list and
                 * then truncate the list.
                 */
                for (i = 0; dependents[i] != NULL; i++) {
                        if ((strcmp(dependents[i], rsrc) == 0) ||
                            (strcmp(dependents[i], "/") == 0)) {
                                free(dependents[i]);
                                dependents[i] = dependents[n - 1];
                                dependents[n] = NULL;
                                i--;
                                n--;
                        }
                }
        }
}