// SPDX-License-Identifier: GPL-2.0
/*
 * DFS referral cache routines
 *
 * Copyright (c) 2018-2019 Paulo Alcantara <palcantara@suse.de>
 */

#include <linux/jhash.h>
#include <linux/ktime.h>
#include <linux/slab.h>
#include <linux/proc_fs.h>
#include <linux/nls.h>
#include <linux/workqueue.h>
#include "cifsglob.h"
#include "smb2pdu.h"
#include "smb2proto.h"
#include "cifsproto.h"
#include "cifs_debug.h"
#include "cifs_unicode.h"
#include "smb2glob.h"
#include "fs_context.h"

#include "dfs_cache.h"

#define CACHE_HTABLE_SIZE 32
#define CACHE_MAX_ENTRIES 64

#define IS_INTERLINK_SET(v) ((v) & (DFSREF_REFERRAL_SERVER | \
                                    DFSREF_STORAGE_SERVER))

struct cache_dfs_tgt {
        char *name;
        int path_consumed;
        struct list_head list;
};

struct cache_entry {
        struct hlist_node hlist;
        const char *path;
        int ttl;
        int srvtype;
        int flags;
        struct timespec64 etime;
        int path_consumed;
        int numtgts;
        struct list_head tlist;
        struct cache_dfs_tgt *tgthint;
};

struct vol_info {
        char *fullpath;
        spinlock_t ctx_lock;
        struct smb3_fs_context ctx;
        char *mntdata;
        struct list_head list;
        struct list_head rlist;
        struct kref refcnt;
};

static struct kmem_cache *cache_slab __read_mostly;
static struct workqueue_struct *dfscache_wq __read_mostly;

static int cache_ttl;
static DEFINE_SPINLOCK(cache_ttl_lock);

static struct nls_table *cache_nlsc;

/*
 * Number of entries in the cache
 */
static atomic_t cache_count;

static struct hlist_head cache_htable[CACHE_HTABLE_SIZE];
static DECLARE_RWSEM(htable_rw_lock);

static LIST_HEAD(vol_list);
static DEFINE_SPINLOCK(vol_list_lock);

static void refresh_cache_worker(struct work_struct *work);

static DECLARE_DELAYED_WORK(refresh_task, refresh_cache_worker);

static int get_normalized_path(const char *path, char **npath)
{
        if (!path || strlen(path) < 3 || (*path != '\\' && *path != '/'))
                return -EINVAL;

        if (*path == '\\') {
                *npath = (char *)path;
        } else {
                *npath = kstrndup(path, strlen(path), GFP_KERNEL);
                if (!*npath)
                        return -ENOMEM;
                convert_delimiter(*npath, '\\');
        }
        return 0;
}

static inline void free_normalized_path(const char *path, char *npath)
{
        if (path != npath)
                kfree(npath);
}

static inline bool cache_entry_expired(const struct cache_entry *ce)
{
        struct timespec64 ts;

        ktime_get_coarse_real_ts64(&ts);
        return timespec64_compare(&ts, &ce->etime) >= 0;
}

static inline void free_tgts(struct cache_entry *ce)
{
        struct cache_dfs_tgt *t, *n;

        list_for_each_entry_safe(t, n, &ce->tlist, list) {
                list_del(&t->list);
                kfree(t->name);
                kfree(t);
        }
}

static inline void flush_cache_ent(struct cache_entry *ce)
{
        hlist_del_init(&ce->hlist);
        kfree(ce->path);
        free_tgts(ce);
        atomic_dec(&cache_count);
        kmem_cache_free(cache_slab, ce);
}

static void flush_cache_ents(void)
{
        int i;

        for (i = 0; i < CACHE_HTABLE_SIZE; i++) {
                struct hlist_head *l = &cache_htable[i];
                struct hlist_node *n;
                struct cache_entry *ce;

                hlist_for_each_entry_safe(ce, n, l, hlist) {
                        if (!hlist_unhashed(&ce->hlist))
                                flush_cache_ent(ce);
                }
        }
}

/*
 * dfs cache /proc file
 */
static int dfscache_proc_show(struct seq_file *m, void *v)
{
        int i;
        struct cache_entry *ce;
        struct cache_dfs_tgt *t;

        seq_puts(m, "DFS cache\n---------\n");

        down_read(&htable_rw_lock);
        for (i = 0; i < CACHE_HTABLE_SIZE; i++) {
                struct hlist_head *l = &cache_htable[i];

                hlist_for_each_entry(ce, l, hlist) {
                        if (hlist_unhashed(&ce->hlist))
                                continue;

                        seq_printf(m,
                                   "cache entry: path=%s,type=%s,ttl=%d,etime=%ld,"
                                   "interlink=%s,path_consumed=%d,expired=%s\n",
                                   ce->path,
                                   ce->srvtype == DFS_TYPE_ROOT ? "root" : "link",
                                   ce->ttl, ce->etime.tv_nsec,
                                   IS_INTERLINK_SET(ce->flags) ? "yes" : "no",
                                   ce->path_consumed,
                                   cache_entry_expired(ce) ? "yes" : "no");

                        list_for_each_entry(t, &ce->tlist, list) {
                                seq_printf(m, "  %s%s\n",
                                           t->name,
                                           ce->tgthint == t ? " (target hint)" : "");
                        }
                }
        }
        up_read(&htable_rw_lock);

        return 0;
}

static ssize_t dfscache_proc_write(struct file *file, const char __user *buffer,
                                   size_t count, loff_t *ppos)
{
        char c;
        int rc;

        rc = get_user(c, buffer);
        if (rc)
                return rc;

        if (c != '0')
                return -EINVAL;

        cifs_dbg(FYI, "clearing dfs cache\n");

        down_write(&htable_rw_lock);
        flush_cache_ents();
        up_write(&htable_rw_lock);

        return count;
}

static int dfscache_proc_open(struct inode *inode, struct file *file)
{
        return single_open(file, dfscache_proc_show, NULL);
}

const struct proc_ops dfscache_proc_ops = {
        .proc_open      = dfscache_proc_open,
        .proc_read      = seq_read,
        .proc_lseek     = seq_lseek,
        .proc_release   = single_release,
        .proc_write     = dfscache_proc_write,
};

#ifdef CONFIG_CIFS_DEBUG2
static inline void dump_tgts(const struct cache_entry *ce)
{
        struct cache_dfs_tgt *t;

        cifs_dbg(FYI, "target list:\n");
        list_for_each_entry(t, &ce->tlist, list) {
                cifs_dbg(FYI, "  %s%s\n", t->name,
                         ce->tgthint == t ? " (target hint)" : "");
        }
}

static inline void dump_ce(const struct cache_entry *ce)
{
        cifs_dbg(FYI, "cache entry: path=%s,type=%s,ttl=%d,etime=%ld,interlink=%s,path_consumed=%d,expired=%s\n",
                 ce->path,
                 ce->srvtype == DFS_TYPE_ROOT ? "root" : "link", ce->ttl,
                 ce->etime.tv_nsec,
                 IS_INTERLINK_SET(ce->flags) ? "yes" : "no",
                 ce->path_consumed,
                 cache_entry_expired(ce) ? "yes" : "no");
        dump_tgts(ce);
}

static inline void dump_refs(const struct dfs_info3_param *refs, int numrefs)
{
        int i;

        cifs_dbg(FYI, "DFS referrals returned by the server:\n");
        for (i = 0; i < numrefs; i++) {
                const struct dfs_info3_param *ref = &refs[i];

                cifs_dbg(FYI,
                         "\n"
                         "flags:         0x%x\n"
                         "path_consumed: %d\n"
                         "server_type:   0x%x\n"
                         "ref_flag:      0x%x\n"
                         "path_name:     %s\n"
                         "node_name:     %s\n"
                         "ttl:           %d (%dm)\n",
                         ref->flags, ref->path_consumed, ref->server_type,
                         ref->ref_flag, ref->path_name, ref->node_name,
                         ref->ttl, ref->ttl / 60);
        }
}
#else
#define dump_tgts(e)
#define dump_ce(e)
#define dump_refs(r, n)
#endif

/**
 * dfs_cache_init - Initialize DFS referral cache.
 *
 * Return zero if initialized successfully, otherwise non-zero.
 */
int dfs_cache_init(void)
{
        int rc;
        int i;

        dfscache_wq = alloc_workqueue("cifs-dfscache",
                                      WQ_FREEZABLE | WQ_MEM_RECLAIM, 1);
        if (!dfscache_wq)
                return -ENOMEM;

        cache_slab = kmem_cache_create("cifs_dfs_cache",
                                       sizeof(struct cache_entry), 0,
                                       SLAB_HWCACHE_ALIGN, NULL);
        if (!cache_slab) {
                rc = -ENOMEM;
                goto out_destroy_wq;
        }

        for (i = 0; i < CACHE_HTABLE_SIZE; i++)
                INIT_HLIST_HEAD(&cache_htable[i]);

        atomic_set(&cache_count, 0);
        cache_nlsc = load_nls_default();

        cifs_dbg(FYI, "%s: initialized DFS referral cache\n", __func__);
        return 0;

out_destroy_wq:
        destroy_workqueue(dfscache_wq);
        return rc;
}

static inline unsigned int cache_entry_hash(const void *data, int size)
{
        unsigned int h;

        h = jhash(data, size, 0);
        return h & (CACHE_HTABLE_SIZE - 1);
}

/* Check whether second path component of @path is SYSVOL or NETLOGON */
static inline bool is_sysvol_or_netlogon(const char *path)
{
        const char *s;
        char sep = path[0];

        s = strchr(path + 1, sep) + 1;
        return !strncasecmp(s, "sysvol", strlen("sysvol")) ||
                !strncasecmp(s, "netlogon", strlen("netlogon"));
}

/* Return target hint of a DFS cache entry */
static inline char *get_tgt_name(const struct cache_entry *ce)
{
        struct cache_dfs_tgt *t = ce->tgthint;

        return t ? t->name : ERR_PTR(-ENOENT);
}

/* Return expire time out of a new entry's TTL */
static inline struct timespec64 get_expire_time(int ttl)
{
        struct timespec64 ts = {
                .tv_sec = ttl,
                .tv_nsec = 0,
        };
        struct timespec64 now;

        ktime_get_coarse_real_ts64(&now);
        return timespec64_add(now, ts);
}

/* Allocate a new DFS target */
static struct cache_dfs_tgt *alloc_target(const char *name, int path_consumed)
{
        struct cache_dfs_tgt *t;

        t = kmalloc(sizeof(*t), GFP_ATOMIC);
        if (!t)
                return ERR_PTR(-ENOMEM);
        t->name = kstrndup(name, strlen(name), GFP_ATOMIC);
        if (!t->name) {
                kfree(t);
                return ERR_PTR(-ENOMEM);
        }
        t->path_consumed = path_consumed;
        INIT_LIST_HEAD(&t->list);
        return t;
}

/*
 * Copy DFS referral information to a cache entry and conditionally update
 * target hint.
 */
static int copy_ref_data(const struct dfs_info3_param *refs, int numrefs,
                         struct cache_entry *ce, const char *tgthint)
{
        int i;

        ce->ttl = refs[0].ttl;
        ce->etime = get_expire_time(ce->ttl);
        ce->srvtype = refs[0].server_type;
        ce->flags = refs[0].ref_flag;
        ce->path_consumed = refs[0].path_consumed;

        for (i = 0; i < numrefs; i++) {
                struct cache_dfs_tgt *t;

                t = alloc_target(refs[i].node_name, refs[i].path_consumed);
                if (IS_ERR(t)) {
                        free_tgts(ce);
                        return PTR_ERR(t);
                }
                if (tgthint && !strcasecmp(t->name, tgthint)) {
                        list_add(&t->list, &ce->tlist);
                        tgthint = NULL;
                } else {
                        list_add_tail(&t->list, &ce->tlist);
                }
                ce->numtgts++;
        }

        ce->tgthint = list_first_entry_or_null(&ce->tlist,
                                               struct cache_dfs_tgt, list);

        return 0;
}

/* Allocate a new cache entry */
static struct cache_entry *alloc_cache_entry(const char *path,
                                             const struct dfs_info3_param *refs,
                                             int numrefs)
{
        struct cache_entry *ce;
        int rc;

        ce = kmem_cache_zalloc(cache_slab, GFP_KERNEL);
        if (!ce)
                return ERR_PTR(-ENOMEM);

        ce->path = kstrndup(path, strlen(path), GFP_KERNEL);
        if (!ce->path) {
                kmem_cache_free(cache_slab, ce);
                return ERR_PTR(-ENOMEM);
        }
        INIT_HLIST_NODE(&ce->hlist);
        INIT_LIST_HEAD(&ce->tlist);

        rc = copy_ref_data(refs, numrefs, ce, NULL);
        if (rc) {
                kfree(ce->path);
                kmem_cache_free(cache_slab, ce);
                ce = ERR_PTR(rc);
        }
        return ce;
}

/* Must be called with htable_rw_lock held */
static void remove_oldest_entry(void)
{
        int i;
        struct cache_entry *ce;
        struct cache_entry *to_del = NULL;

        for (i = 0; i < CACHE_HTABLE_SIZE; i++) {
                struct hlist_head *l = &cache_htable[i];

                hlist_for_each_entry(ce, l, hlist) {
                        if (hlist_unhashed(&ce->hlist))
                                continue;
                        if (!to_del || timespec64_compare(&ce->etime,
                                                          &to_del->etime) < 0)
                                to_del = ce;
                }
        }

        if (!to_del) {
                cifs_dbg(FYI, "%s: no entry to remove\n", __func__);
                return;
        }

        cifs_dbg(FYI, "%s: removing entry\n", __func__);
        dump_ce(to_del);
        flush_cache_ent(to_del);
}

/* Add a new DFS cache entry */
static int add_cache_entry(const char *path, unsigned int hash,
                           struct dfs_info3_param *refs, int numrefs)
{
        struct cache_entry *ce;

        ce = alloc_cache_entry(path, refs, numrefs);
        if (IS_ERR(ce))
                return PTR_ERR(ce);

        spin_lock(&cache_ttl_lock);
        if (!cache_ttl) {
                cache_ttl = ce->ttl;
                queue_delayed_work(dfscache_wq, &refresh_task, cache_ttl * HZ);
        } else {
                cache_ttl = min_t(int, cache_ttl, ce->ttl);
                mod_delayed_work(dfscache_wq, &refresh_task, cache_ttl * HZ);
        }
        spin_unlock(&cache_ttl_lock);

        down_write(&htable_rw_lock);
        hlist_add_head(&ce->hlist, &cache_htable[hash]);
        dump_ce(ce);
        up_write(&htable_rw_lock);

        return 0;
}

static struct cache_entry *__lookup_cache_entry(const char *path)
{
        struct cache_entry *ce;
        unsigned int h;
        bool found = false;

        h = cache_entry_hash(path, strlen(path));

        hlist_for_each_entry(ce, &cache_htable[h], hlist) {
                if (!strcasecmp(path, ce->path)) {
                        found = true;
                        dump_ce(ce);
                        break;
                }
        }

        if (!found)
                ce = ERR_PTR(-ENOENT);
        return ce;
}

/*
 * Find a DFS cache entry in hash table and optionally check prefix path against
 * @path.
 * Use whole path components in the match.
 * Must be called with htable_rw_lock held.
 *
 * Return ERR_PTR(-ENOENT) if the entry is not found.
 */
static struct cache_entry *lookup_cache_entry(const char *path, unsigned int *hash)
{
        struct cache_entry *ce = ERR_PTR(-ENOENT);
        unsigned int h;
        int cnt = 0;
        char *npath;
        char *s, *e;
        char sep;

        npath = kstrndup(path, strlen(path), GFP_KERNEL);
        if (!npath)
                return ERR_PTR(-ENOMEM);

        s = npath;
        sep = *npath;
        while ((s = strchr(s, sep)) && ++cnt < 3)
                s++;

        if (cnt < 3) {
                h = cache_entry_hash(path, strlen(path));
                ce = __lookup_cache_entry(path);
                goto out;
        }
        /*
         * Handle paths that have more than two path components and are a complete prefix of the DFS
         * referral request path (@path).
         *
         * See MS-DFSC 3.2.5.5 "Receiving a Root Referral Request or Link Referral Request".
         */
        h = cache_entry_hash(npath, strlen(npath));
        e = npath + strlen(npath) - 1;
        while (e > s) {
                char tmp;

                /* skip separators */
                while (e > s && *e == sep)
                        e--;
                if (e == s)
                        goto out;

                tmp = *(e+1);
                *(e+1) = 0;

                ce = __lookup_cache_entry(npath);
                if (!IS_ERR(ce)) {
                        h = cache_entry_hash(npath, strlen(npath));
                        break;
                }

                *(e+1) = tmp;
                /* backward until separator */
                while (e > s && *e != sep)
                        e--;
        }
out:
        if (hash)
                *hash = h;
        kfree(npath);
        return ce;
}

static void __vol_release(struct vol_info *vi)
{
        kfree(vi->fullpath);
        kfree(vi->mntdata);
        smb3_cleanup_fs_context_contents(&vi->ctx);
        kfree(vi);
}

static void vol_release(struct kref *kref)
{
        struct vol_info *vi = container_of(kref, struct vol_info, refcnt);

        spin_lock(&vol_list_lock);
        list_del(&vi->list);
        spin_unlock(&vol_list_lock);
        __vol_release(vi);
}

static inline void free_vol_list(void)
{
        struct vol_info *vi, *nvi;

        list_for_each_entry_safe(vi, nvi, &vol_list, list) {
                list_del_init(&vi->list);
                __vol_release(vi);
        }
}

/**
 * dfs_cache_destroy - destroy DFS referral cache
 */
void dfs_cache_destroy(void)
{
        cancel_delayed_work_sync(&refresh_task);
        unload_nls(cache_nlsc);
        free_vol_list();
        flush_cache_ents();
        kmem_cache_destroy(cache_slab);
        destroy_workqueue(dfscache_wq);

        cifs_dbg(FYI, "%s: destroyed DFS referral cache\n", __func__);
}

/* Must be called with htable_rw_lock held */
static int __update_cache_entry(const char *path,
                                const struct dfs_info3_param *refs,
                                int numrefs)
{
        int rc;
        struct cache_entry *ce;
        char *s, *th = NULL;

        ce = lookup_cache_entry(path, NULL);
        if (IS_ERR(ce))
                return PTR_ERR(ce);

        if (ce->tgthint) {
                s = ce->tgthint->name;
                th = kstrndup(s, strlen(s), GFP_ATOMIC);
                if (!th)
                        return -ENOMEM;
        }

        free_tgts(ce);
        ce->numtgts = 0;

        rc = copy_ref_data(refs, numrefs, ce, th);

        kfree(th);

        return rc;
}

static int get_dfs_referral(const unsigned int xid, struct cifs_ses *ses,
                            const struct nls_table *nls_codepage, int remap,
                            const char *path,  struct dfs_info3_param **refs,
                            int *numrefs)
{
        cifs_dbg(FYI, "%s: get an DFS referral for %s\n", __func__, path);

        if (!ses || !ses->server || !ses->server->ops->get_dfs_refer)
                return -EOPNOTSUPP;
        if (unlikely(!nls_codepage))
                return -EINVAL;

        *refs = NULL;
        *numrefs = 0;

        return ses->server->ops->get_dfs_refer(xid, ses, path, refs, numrefs,
                                               nls_codepage, remap);
}

/* Update an expired cache entry by getting a new DFS referral from server */
static int update_cache_entry(const char *path,
                              const struct dfs_info3_param *refs,
                              int numrefs)
{

        int rc;

        down_write(&htable_rw_lock);
        rc = __update_cache_entry(path, refs, numrefs);
        up_write(&htable_rw_lock);

        return rc;
}

/*
 * Find, create or update a DFS cache entry.
 *
 * If the entry wasn't found, it will create a new one. Or if it was found but
 * expired, then it will update the entry accordingly.
 *
 * For interlinks, __cifs_dfs_mount() and expand_dfs_referral() are supposed to
 * handle them properly.
 */
static int __dfs_cache_find(const unsigned int xid, struct cifs_ses *ses,
                            const struct nls_table *nls_codepage, int remap,
                            const char *path, bool noreq)
{
        int rc;
        unsigned int hash;
        struct cache_entry *ce;
        struct dfs_info3_param *refs = NULL;
        int numrefs = 0;
        bool newent = false;

        cifs_dbg(FYI, "%s: search path: %s\n", __func__, path);

        down_read(&htable_rw_lock);

        ce = lookup_cache_entry(path, &hash);

        /*
         * If @noreq is set, no requests will be sent to the server. Just return
         * the cache entry.
         */
        if (noreq) {
                up_read(&htable_rw_lock);
                return PTR_ERR_OR_ZERO(ce);
        }

        if (!IS_ERR(ce)) {
                if (!cache_entry_expired(ce)) {
                        dump_ce(ce);
                        up_read(&htable_rw_lock);
                        return 0;
                }
        } else {
                newent = true;
        }

        up_read(&htable_rw_lock);

        /*
         * No entry was found.
         *
         * Request a new DFS referral in order to create a new cache entry, or
         * updating an existing one.
         */
        rc = get_dfs_referral(xid, ses, nls_codepage, remap, path,
                              &refs, &numrefs);
        if (rc)
                return rc;

        dump_refs(refs, numrefs);

        if (!newent) {
                rc = update_cache_entry(path, refs, numrefs);
                goto out_free_refs;
        }

        if (atomic_read(&cache_count) >= CACHE_MAX_ENTRIES) {
                cifs_dbg(FYI, "%s: reached max cache size (%d)\n",
                         __func__, CACHE_MAX_ENTRIES);
                down_write(&htable_rw_lock);
                remove_oldest_entry();
                up_write(&htable_rw_lock);
        }

        rc = add_cache_entry(path, hash, refs, numrefs);
        if (!rc)
                atomic_inc(&cache_count);

out_free_refs:
        free_dfs_info_array(refs, numrefs);
        return rc;
}

/*
 * Set up a DFS referral from a given cache entry.
 *
 * Must be called with htable_rw_lock held.
 */
static int setup_referral(const char *path, struct cache_entry *ce,
                          struct dfs_info3_param *ref, const char *target)
{
        int rc;

        cifs_dbg(FYI, "%s: set up new ref\n", __func__);

        memset(ref, 0, sizeof(*ref));

        ref->path_name = kstrndup(path, strlen(path), GFP_ATOMIC);
        if (!ref->path_name)
                return -ENOMEM;

        ref->node_name = kstrndup(target, strlen(target), GFP_ATOMIC);
        if (!ref->node_name) {
                rc = -ENOMEM;
                goto err_free_path;
        }

        ref->path_consumed = ce->path_consumed;
        ref->ttl = ce->ttl;
        ref->server_type = ce->srvtype;
        ref->ref_flag = ce->flags;

        return 0;

err_free_path:
        kfree(ref->path_name);
        ref->path_name = NULL;
        return rc;
}

/* Return target list of a DFS cache entry */
static int get_targets(struct cache_entry *ce, struct dfs_cache_tgt_list *tl)
{
        int rc;
        struct list_head *head = &tl->tl_list;
        struct cache_dfs_tgt *t;
        struct dfs_cache_tgt_iterator *it, *nit;

        memset(tl, 0, sizeof(*tl));
        INIT_LIST_HEAD(head);

        list_for_each_entry(t, &ce->tlist, list) {
                it = kzalloc(sizeof(*it), GFP_ATOMIC);
                if (!it) {
                        rc = -ENOMEM;
                        goto err_free_it;
                }

                it->it_name = kstrndup(t->name, strlen(t->name), GFP_ATOMIC);
                if (!it->it_name) {
                        kfree(it);
                        rc = -ENOMEM;
                        goto err_free_it;
                }
                it->it_path_consumed = t->path_consumed;

                if (ce->tgthint == t)
                        list_add(&it->it_list, head);
                else
                        list_add_tail(&it->it_list, head);
        }

        tl->tl_numtgts = ce->numtgts;

        return 0;

err_free_it:
        list_for_each_entry_safe(it, nit, head, it_list) {
                kfree(it->it_name);
                kfree(it);
        }
        return rc;
}

/**
 * dfs_cache_find - find a DFS cache entry
 *
 * If it doesn't find the cache entry, then it will get a DFS referral
 * for @path and create a new entry.
 *
 * In case the cache entry exists but expired, it will get a DFS referral
 * for @path and then update the respective cache entry.
 *
 * These parameters are passed down to the get_dfs_refer() call if it
 * needs to be issued:
 * @xid: syscall xid
 * @ses: smb session to issue the request on
 * @nls_codepage: charset conversion
 * @remap: path character remapping type
 * @path: path to lookup in DFS referral cache.
 *
 * @ref: when non-NULL, store single DFS referral result in it.
 * @tgt_list: when non-NULL, store complete DFS target list in it.
 *
 * Return zero if the target was found, otherwise non-zero.
 */
int dfs_cache_find(const unsigned int xid, struct cifs_ses *ses,
                   const struct nls_table *nls_codepage, int remap,
                   const char *path, struct dfs_info3_param *ref,
                   struct dfs_cache_tgt_list *tgt_list)
{
        int rc;
        char *npath;
        struct cache_entry *ce;

        rc = get_normalized_path(path, &npath);
        if (rc)
                return rc;

        rc = __dfs_cache_find(xid, ses, nls_codepage, remap, npath, false);
        if (rc)
                goto out_free_path;

        down_read(&htable_rw_lock);

        ce = lookup_cache_entry(npath, NULL);
        if (IS_ERR(ce)) {
                up_read(&htable_rw_lock);
                rc = PTR_ERR(ce);
                goto out_free_path;
        }

        if (ref)
                rc = setup_referral(path, ce, ref, get_tgt_name(ce));
        else
                rc = 0;
        if (!rc && tgt_list)
                rc = get_targets(ce, tgt_list);

        up_read(&htable_rw_lock);

out_free_path:
        free_normalized_path(path, npath);
        return rc;
}

/**
 * dfs_cache_noreq_find - find a DFS cache entry without sending any requests to
 * the currently connected server.
 *
 * NOTE: This function will neither update a cache entry in case it was
 * expired, nor create a new cache entry if @path hasn't been found. It heavily
 * relies on an existing cache entry.
 *
 * @path: path to lookup in the DFS referral cache.
 * @ref: when non-NULL, store single DFS referral result in it.
 * @tgt_list: when non-NULL, store complete DFS target list in it.
 *
 * Return 0 if successful.
 * Return -ENOENT if the entry was not found.
 * Return non-zero for other errors.
 */
int dfs_cache_noreq_find(const char *path, struct dfs_info3_param *ref,
                         struct dfs_cache_tgt_list *tgt_list)
{
        int rc;
        char *npath;
        struct cache_entry *ce;

        rc = get_normalized_path(path, &npath);
        if (rc)
                return rc;

        cifs_dbg(FYI, "%s: path: %s\n", __func__, npath);

        down_read(&htable_rw_lock);

        ce = lookup_cache_entry(npath, NULL);
        if (IS_ERR(ce)) {
                rc = PTR_ERR(ce);
                goto out_unlock;
        }

        if (ref)
                rc = setup_referral(path, ce, ref, get_tgt_name(ce));
        else
                rc = 0;
        if (!rc && tgt_list)
                rc = get_targets(ce, tgt_list);

out_unlock:
        up_read(&htable_rw_lock);
        free_normalized_path(path, npath);

        return rc;
}

/**
 * dfs_cache_update_tgthint - update target hint of a DFS cache entry
 *
 * If it doesn't find the cache entry, then it will get a DFS referral for @path
 * and create a new entry.
 *
 * In case the cache entry exists but expired, it will get a DFS referral
 * for @path and then update the respective cache entry.
 *
 * @xid: syscall id
 * @ses: smb session
 * @nls_codepage: charset conversion
 * @remap: type of character remapping for paths
 * @path: path to lookup in DFS referral cache.
 * @it: DFS target iterator
 *
 * Return zero if the target hint was updated successfully, otherwise non-zero.
 */
int dfs_cache_update_tgthint(const unsigned int xid, struct cifs_ses *ses,
                             const struct nls_table *nls_codepage, int remap,
                             const char *path,
                             const struct dfs_cache_tgt_iterator *it)
{
        int rc;
        char *npath;
        struct cache_entry *ce;
        struct cache_dfs_tgt *t;

        rc = get_normalized_path(path, &npath);
        if (rc)
                return rc;

        cifs_dbg(FYI, "%s: update target hint - path: %s\n", __func__, npath);

        rc = __dfs_cache_find(xid, ses, nls_codepage, remap, npath, false);
        if (rc)
                goto out_free_path;

        down_write(&htable_rw_lock);

        ce = lookup_cache_entry(npath, NULL);
        if (IS_ERR(ce)) {
                rc = PTR_ERR(ce);
                goto out_unlock;
        }

        t = ce->tgthint;

        if (likely(!strcasecmp(it->it_name, t->name)))
                goto out_unlock;

        list_for_each_entry(t, &ce->tlist, list) {
                if (!strcasecmp(t->name, it->it_name)) {
                        ce->tgthint = t;
                        cifs_dbg(FYI, "%s: new target hint: %s\n", __func__,
                                 it->it_name);
                        break;
                }
        }

out_unlock:
        up_write(&htable_rw_lock);
out_free_path:
        free_normalized_path(path, npath);

        return rc;
}

/**
 * dfs_cache_noreq_update_tgthint - update target hint of a DFS cache entry
 * without sending any requests to the currently connected server.
 *
 * NOTE: This function will neither update a cache entry in case it was
 * expired, nor create a new cache entry if @path hasn't been found. It heavily
 * relies on an existing cache entry.
 *
 * @path: path to lookup in DFS referral cache.
 * @it: target iterator which contains the target hint to update the cache
 * entry with.
 *
 * Return zero if the target hint was updated successfully, otherwise non-zero.
 */
int dfs_cache_noreq_update_tgthint(const char *path,
                                   const struct dfs_cache_tgt_iterator *it)
{
        int rc;
        char *npath;
        struct cache_entry *ce;
        struct cache_dfs_tgt *t;

        if (!it)
                return -EINVAL;

        rc = get_normalized_path(path, &npath);
        if (rc)
                return rc;

        cifs_dbg(FYI, "%s: path: %s\n", __func__, npath);

        down_write(&htable_rw_lock);

        ce = lookup_cache_entry(npath, NULL);
        if (IS_ERR(ce)) {
                rc = PTR_ERR(ce);
                goto out_unlock;
        }

        rc = 0;
        t = ce->tgthint;

        if (unlikely(!strcasecmp(it->it_name, t->name)))
                goto out_unlock;

        list_for_each_entry(t, &ce->tlist, list) {
                if (!strcasecmp(t->name, it->it_name)) {
                        ce->tgthint = t;
                        cifs_dbg(FYI, "%s: new target hint: %s\n", __func__,
                                 it->it_name);
                        break;
                }
        }

out_unlock:
        up_write(&htable_rw_lock);
        free_normalized_path(path, npath);

        return rc;
}

/**
 * dfs_cache_get_tgt_referral - returns a DFS referral (@ref) from a given
 * target iterator (@it).
 *
 * @path: path to lookup in DFS referral cache.
 * @it: DFS target iterator.
 * @ref: DFS referral pointer to set up the gathered information.
 *
 * Return zero if the DFS referral was set up correctly, otherwise non-zero.
 */
int dfs_cache_get_tgt_referral(const char *path,
                               const struct dfs_cache_tgt_iterator *it,
                               struct dfs_info3_param *ref)
{
        int rc;
        char *npath;
        struct cache_entry *ce;

        if (!it || !ref)
                return -EINVAL;

        rc = get_normalized_path(path, &npath);
        if (rc)
                return rc;

        cifs_dbg(FYI, "%s: path: %s\n", __func__, npath);

        down_read(&htable_rw_lock);

        ce = lookup_cache_entry(npath, NULL);
        if (IS_ERR(ce)) {
                rc = PTR_ERR(ce);
                goto out_unlock;
        }

        cifs_dbg(FYI, "%s: target name: %s\n", __func__, it->it_name);

        rc = setup_referral(path, ce, ref, it->it_name);

out_unlock:
        up_read(&htable_rw_lock);
        free_normalized_path(path, npath);

        return rc;
}

/**
 * dfs_cache_add_vol - add a cifs context during mount() that will be handled by
 * DFS cache refresh worker.
 *
 * @mntdata: mount data.
 * @ctx: cifs context.
 * @fullpath: origin full path.
 *
 * Return zero if context was set up correctly, otherwise non-zero.
 */
int dfs_cache_add_vol(char *mntdata, struct smb3_fs_context *ctx, const char *fullpath)
{
        int rc;
        struct vol_info *vi;

        if (!ctx || !fullpath || !mntdata)
                return -EINVAL;

        cifs_dbg(FYI, "%s: fullpath: %s\n", __func__, fullpath);

        vi = kzalloc(sizeof(*vi), GFP_KERNEL);
        if (!vi)
                return -ENOMEM;

        vi->fullpath = kstrndup(fullpath, strlen(fullpath), GFP_KERNEL);
        if (!vi->fullpath) {
                rc = -ENOMEM;
                goto err_free_vi;
        }

        rc = smb3_fs_context_dup(&vi->ctx, ctx);
        if (rc)
                goto err_free_fullpath;

        vi->mntdata = mntdata;
        spin_lock_init(&vi->ctx_lock);
        kref_init(&vi->refcnt);

        spin_lock(&vol_list_lock);
        list_add_tail(&vi->list, &vol_list);
        spin_unlock(&vol_list_lock);

        return 0;

err_free_fullpath:
        kfree(vi->fullpath);
err_free_vi:
        kfree(vi);
        return rc;
}

/* Must be called with vol_list_lock held */
static struct vol_info *find_vol(const char *fullpath)
{
        struct vol_info *vi;

        list_for_each_entry(vi, &vol_list, list) {
                cifs_dbg(FYI, "%s: vi->fullpath: %s\n", __func__, vi->fullpath);
                if (!strcasecmp(vi->fullpath, fullpath))
                        return vi;
        }
        return ERR_PTR(-ENOENT);
}

/**
 * dfs_cache_update_vol - update vol info in DFS cache after failover
 *
 * @fullpath: fullpath to look up in volume list.
 * @server: TCP ses pointer.
 *
 * Return zero if volume was updated, otherwise non-zero.
 */
int dfs_cache_update_vol(const char *fullpath, struct TCP_Server_Info *server)
{
        struct vol_info *vi;

        if (!fullpath || !server)
                return -EINVAL;

        cifs_dbg(FYI, "%s: fullpath: %s\n", __func__, fullpath);

        spin_lock(&vol_list_lock);
        vi = find_vol(fullpath);
        if (IS_ERR(vi)) {
                spin_unlock(&vol_list_lock);
                return PTR_ERR(vi);
        }
        kref_get(&vi->refcnt);
        spin_unlock(&vol_list_lock);

        cifs_dbg(FYI, "%s: updating volume info\n", __func__);
        spin_lock(&vi->ctx_lock);
        memcpy(&vi->ctx.dstaddr, &server->dstaddr,
               sizeof(vi->ctx.dstaddr));
        spin_unlock(&vi->ctx_lock);

        kref_put(&vi->refcnt, vol_release);

        return 0;
}

/**
 * dfs_cache_del_vol - remove volume info in DFS cache during umount()
 *
 * @fullpath: fullpath to look up in volume list.
 */
void dfs_cache_del_vol(const char *fullpath)
{
        struct vol_info *vi;

        if (!fullpath || !*fullpath)
                return;

        cifs_dbg(FYI, "%s: fullpath: %s\n", __func__, fullpath);

        spin_lock(&vol_list_lock);
        vi = find_vol(fullpath);
        spin_unlock(&vol_list_lock);

        if (!IS_ERR(vi))
                kref_put(&vi->refcnt, vol_release);
}

/**
 * dfs_cache_get_tgt_share - parse a DFS target
 *
 * @path: DFS full path
 * @it: DFS target iterator.
 * @share: tree name.
 * @prefix: prefix path.
 *
 * Return zero if target was parsed correctly, otherwise non-zero.
 */
int dfs_cache_get_tgt_share(char *path, const struct dfs_cache_tgt_iterator *it,
                            char **share, char **prefix)
{
        char *s, sep, *p;
        size_t len;
        size_t plen1, plen2;

        if (!it || !path || !share || !prefix || strlen(path) < it->it_path_consumed)
                return -EINVAL;

        *share = NULL;
        *prefix = NULL;

        sep = it->it_name[0];
        if (sep != '\\' && sep != '/')
                return -EINVAL;

        s = strchr(it->it_name + 1, sep);
        if (!s)
                return -EINVAL;

        /* point to prefix in target node */
        s = strchrnul(s + 1, sep);

        /* extract target share */
        *share = kstrndup(it->it_name, s - it->it_name, GFP_KERNEL);
        if (!*share)
                return -ENOMEM;

        /* skip separator */
        if (*s)
                s++;
        /* point to prefix in DFS path */
        p = path + it->it_path_consumed;
        if (*p == sep)
                p++;

        /* merge prefix paths from DFS path and target node */
        plen1 = it->it_name + strlen(it->it_name) - s;
        plen2 = path + strlen(path) - p;
        if (plen1 || plen2) {
                len = plen1 + plen2 + 2;
                *prefix = kmalloc(len, GFP_KERNEL);
                if (!*prefix) {
                        kfree(*share);
                        *share = NULL;
                        return -ENOMEM;
                }
                if (plen1)
                        scnprintf(*prefix, len, "%.*s%c%.*s", (int)plen1, s, sep, (int)plen2, p);
                else
                        strscpy(*prefix, p, len);
        }
        return 0;
}

/* Get all tcons that are within a DFS namespace and can be refreshed */
static void get_tcons(struct TCP_Server_Info *server, struct list_head *head)
{
        struct cifs_ses *ses;
        struct cifs_tcon *tcon;

        INIT_LIST_HEAD(head);

        spin_lock(&cifs_tcp_ses_lock);
        list_for_each_entry(ses, &server->smb_ses_list, smb_ses_list) {
                list_for_each_entry(tcon, &ses->tcon_list, tcon_list) {
                        if (!tcon->need_reconnect && !tcon->need_reopen_files &&
                            tcon->dfs_path) {
                                tcon->tc_count++;
                                list_add_tail(&tcon->ulist, head);
                        }
                }
                if (ses->tcon_ipc && !ses->tcon_ipc->need_reconnect &&
                    ses->tcon_ipc->dfs_path) {
                        list_add_tail(&ses->tcon_ipc->ulist, head);
                }
        }
        spin_unlock(&cifs_tcp_ses_lock);
}

static bool is_dfs_link(const char *path)
{
        char *s;

        s = strchr(path + 1, '\\');
        if (!s)
                return false;
        return !!strchr(s + 1, '\\');
}

static char *get_dfs_root(const char *path)
{
        char *s, *npath;

        s = strchr(path + 1, '\\');
        if (!s)
                return ERR_PTR(-EINVAL);

        s = strchr(s + 1, '\\');
        if (!s)
                return ERR_PTR(-EINVAL);

        npath = kstrndup(path, s - path, GFP_KERNEL);
        if (!npath)
                return ERR_PTR(-ENOMEM);

        return npath;
}

static inline void put_tcp_server(struct TCP_Server_Info *server)
{
        cifs_put_tcp_session(server, 0);
}

static struct TCP_Server_Info *get_tcp_server(struct smb3_fs_context *ctx)
{
        struct TCP_Server_Info *server;

        server = cifs_find_tcp_session(ctx);
        if (IS_ERR_OR_NULL(server))
                return NULL;

        spin_lock(&GlobalMid_Lock);
        if (server->tcpStatus != CifsGood) {
                spin_unlock(&GlobalMid_Lock);
                put_tcp_server(server);
                return NULL;
        }
        spin_unlock(&GlobalMid_Lock);

        return server;
}

/* Find root SMB session out of a DFS link path */
static struct cifs_ses *find_root_ses(struct vol_info *vi,
                                      struct cifs_tcon *tcon,
                                      const char *path)
{
        char *rpath;
        int rc;
        struct cache_entry *ce;
        struct dfs_info3_param ref = {0};
        char *mdata = NULL, *devname = NULL;
        struct TCP_Server_Info *server;
        struct cifs_ses *ses;
        struct smb3_fs_context ctx = {NULL};

        rpath = get_dfs_root(path);
        if (IS_ERR(rpath))
                return ERR_CAST(rpath);

        down_read(&htable_rw_lock);

        ce = lookup_cache_entry(rpath, NULL);
        if (IS_ERR(ce)) {
                up_read(&htable_rw_lock);
                ses = ERR_CAST(ce);
                goto out;
        }

        rc = setup_referral(path, ce, &ref, get_tgt_name(ce));
        if (rc) {
                up_read(&htable_rw_lock);
                ses = ERR_PTR(rc);
                goto out;
        }

        up_read(&htable_rw_lock);

        mdata = cifs_compose_mount_options(vi->mntdata, rpath, &ref,
                                           &devname);
        free_dfs_info_param(&ref);

        if (IS_ERR(mdata)) {
                ses = ERR_CAST(mdata);
                mdata = NULL;
                goto out;
        }

        rc = cifs_setup_volume_info(&ctx, NULL, devname);

        if (rc) {
                ses = ERR_PTR(rc);
                goto out;
        }

        server = get_tcp_server(&ctx);
        if (!server) {
                ses = ERR_PTR(-EHOSTDOWN);
                goto out;
        }

        ses = cifs_get_smb_ses(server, &ctx);

out:
        smb3_cleanup_fs_context_contents(&ctx);
        kfree(mdata);
        kfree(rpath);
        kfree(devname);

        return ses;
}

/* Refresh DFS cache entry from a given tcon */
static int refresh_tcon(struct vol_info *vi, struct cifs_tcon *tcon)
{
        int rc = 0;
        unsigned int xid;
        char *path, *npath;
        struct cache_entry *ce;
        struct cifs_ses *root_ses = NULL, *ses;
        struct dfs_info3_param *refs = NULL;
        int numrefs = 0;

        xid = get_xid();

        path = tcon->dfs_path + 1;

        rc = get_normalized_path(path, &npath);
        if (rc)
                goto out_free_xid;

        down_read(&htable_rw_lock);

        ce = lookup_cache_entry(npath, NULL);
        if (IS_ERR(ce)) {
                rc = PTR_ERR(ce);
                up_read(&htable_rw_lock);
                goto out_free_path;
        }

        if (!cache_entry_expired(ce)) {
                up_read(&htable_rw_lock);
                goto out_free_path;
        }

        up_read(&htable_rw_lock);

        /* If it's a DFS Link, then use root SMB session for refreshing it */
        if (is_dfs_link(npath)) {
                ses = root_ses = find_root_ses(vi, tcon, npath);
                if (IS_ERR(ses)) {
                        rc = PTR_ERR(ses);
                        root_ses = NULL;
                        goto out_free_path;
                }
        } else {
                ses = tcon->ses;
        }

        rc = get_dfs_referral(xid, ses, cache_nlsc, tcon->remap, npath, &refs,
                              &numrefs);
        if (!rc) {
                dump_refs(refs, numrefs);
                rc = update_cache_entry(npath, refs, numrefs);
                free_dfs_info_array(refs, numrefs);
        }

        if (root_ses)
                cifs_put_smb_ses(root_ses);

out_free_path:
        free_normalized_path(path, npath);

out_free_xid:
        free_xid(xid);
        return rc;
}

/*
 * Worker that will refresh DFS cache based on lowest TTL value from a DFS
 * referral.
 */
static void refresh_cache_worker(struct work_struct *work)
{
        struct vol_info *vi, *nvi;
        struct TCP_Server_Info *server;
        LIST_HEAD(vols);
        LIST_HEAD(tcons);
        struct cifs_tcon *tcon, *ntcon;
        int rc;

        /*
         * Find SMB volumes that are eligible (server->tcpStatus == CifsGood)
         * for refreshing.
         */
        spin_lock(&vol_list_lock);
        list_for_each_entry(vi, &vol_list, list) {
                server = get_tcp_server(&vi->ctx);
                if (!server)
                        continue;

                kref_get(&vi->refcnt);
                list_add_tail(&vi->rlist, &vols);
                put_tcp_server(server);
        }
        spin_unlock(&vol_list_lock);

        /* Walk through all TCONs and refresh any expired cache entry */
        list_for_each_entry_safe(vi, nvi, &vols, rlist) {
                spin_lock(&vi->ctx_lock);
                server = get_tcp_server(&vi->ctx);
                spin_unlock(&vi->ctx_lock);

                if (!server)
                        goto next_vol;

                get_tcons(server, &tcons);
                rc = 0;

                list_for_each_entry_safe(tcon, ntcon, &tcons, ulist) {
                        /*
                         * Skip tcp server if any of its tcons failed to refresh
                         * (possibily due to reconnects).
                         */
                        if (!rc)
                                rc = refresh_tcon(vi, tcon);

                        list_del_init(&tcon->ulist);
                        cifs_put_tcon(tcon);
                }

                put_tcp_server(server);

next_vol:
                list_del_init(&vi->rlist);
                kref_put(&vi->refcnt, vol_release);
        }

        spin_lock(&cache_ttl_lock);
        queue_delayed_work(dfscache_wq, &refresh_task, cache_ttl * HZ);
        spin_unlock(&cache_ttl_lock);
}