cifs: Add DFS cache routines

* Add new dfs_cache.[ch] files

* Add new /proc/fs/cifs/dfscache file
  - dump current cache when read
  - clear current cache when writing "0" to it

* Add delayed_work to periodically refresh cache entries

The new interface will be used for caching DFS referrals, as well as
supporting client target failover.

The DFS cache is a hashtable that maps UNC paths to cache entries.

A cache entry contains:
- the UNC path it is mapped on
- how much the the UNC path the entry consumes
- flags
- a Time-To-Live after which the entry expires
- a list of possible targets (linked lists of UNC paths)
- a "hint target" pointing the last known working target or the first
  target if none were tried. This hint lets cifs.ko remember and try
  working targets first.

* Looking for an entry in the cache is done with dfs_cache_find()
  - if no valid entries are found, a DFS query is made, stored in the
    cache and returned
  - the full target list can be copied and returned to avoid race
    conditions and looped on with the help with the
    dfs_cache_tgt_iterator

* Updating the target hint to the next target is done with
  dfs_cache_update_tgthint()

These functions have a dfs_cache_noreq_XXX() version that doesn't
fetches referrals if no entries are found. These versions don't
require the tcp/ses/tcon/cifs_sb parameters as a result.

Expired entries cannot be used and since they have a pretty short TTL
[1] in order for them to be useful for failover the DFS cache adds a
delayed work called periodically to keep them fresh.

Since we might not have available connections to issue the referral
request when refreshing we need to store volume_info structs with
credentials and other needed info to be able to connect to the right
server.

1: Windows defaults: 5mn for domain-based referrals, 30mn for regular
links
Signed-off-by: Paulo Alcantara <palcantara@suse.de>
Signed-off-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/Makefile

@@ -17,7 +17,7 @@ cifs-$(CONFIG_CIFS_ACL) += cifsacl.o
 
 cifs-$(CONFIG_CIFS_UPCALL) += cifs_spnego.o
 
-cifs-$(CONFIG_CIFS_DFS_UPCALL) += dns_resolve.o cifs_dfs_ref.o
+cifs-$(CONFIG_CIFS_DFS_UPCALL) += dns_resolve.o cifs_dfs_ref.o dfs_cache.o
 
 cifs-$(CONFIG_CIFS_FSCACHE) += fscache.o cache.o
 

fs/cifs/cifs_debug.c

@@ -30,6 +30,9 @@
 #include "cifsproto.h"
 #include "cifs_debug.h"
 #include "cifsfs.h"
+#ifdef CONFIG_CIFS_DFS_UPCALL
+#include "dfs_cache.h"
+#endif
 #ifdef CONFIG_CIFS_SMB_DIRECT
 #include "smbdirect.h"
 #endif
@@ -629,6 +632,11 @@ cifs_proc_init(void)
 		    &cifs_security_flags_proc_fops);
 	proc_create("LookupCacheEnabled", 0644, proc_fs_cifs,
 		    &cifs_lookup_cache_proc_fops);
+
+#ifdef CONFIG_CIFS_DFS_UPCALL
+	proc_create("dfscache", 0644, proc_fs_cifs, &dfscache_proc_fops);
+#endif
+
 #ifdef CONFIG_CIFS_SMB_DIRECT
 	proc_create("rdma_readwrite_threshold", 0644, proc_fs_cifs,
 		&cifs_rdma_readwrite_threshold_proc_fops);
@@ -663,6 +671,10 @@ cifs_proc_clean(void)
 	remove_proc_entry("SecurityFlags", proc_fs_cifs);
 	remove_proc_entry("LinuxExtensionsEnabled", proc_fs_cifs);
 	remove_proc_entry("LookupCacheEnabled", proc_fs_cifs);
+
+#ifdef CONFIG_CIFS_DFS_UPCALL
+	remove_proc_entry("dfscache", proc_fs_cifs);
+#endif
 #ifdef CONFIG_CIFS_SMB_DIRECT
 	remove_proc_entry("rdma_readwrite_threshold", proc_fs_cifs);
 	remove_proc_entry("smbd_max_frmr_depth", proc_fs_cifs);

fs/cifs/cifsglob.h

@@ -1014,6 +1014,11 @@ struct cifs_tcon {
 	struct list_head pending_opens;	/* list of incomplete opens */
 	struct cached_fid crfid; /* Cached root fid */
 	/* BB add field for back pointer to sb struct(s)? */
+#ifdef CONFIG_CIFS_DFS_UPCALL
+	char *dfs_path;
+	int remap:2;
+	struct list_head ulist; /* cache update list */
+#endif
 };
 
 /*

fs/cifs/cifsproto.h

@@ -527,6 +527,9 @@ extern int SMBencrypt(unsigned char *passwd, const unsigned char *c8,
 extern void
 cifs_cleanup_volume_info_contents(struct smb_vol *volume_info);
 
+extern struct TCP_Server_Info *
+cifs_find_tcp_session(struct smb_vol *vol);
+
 void cifs_readdata_release(struct kref *refcount);
 int cifs_async_readv(struct cifs_readdata *rdata);
 int cifs_readv_receive(struct TCP_Server_Info *server, struct mid_q_entry *mid);

fs/cifs/connect.c

@@ -2295,7 +2295,7 @@ static int match_server(struct TCP_Server_Info *server, struct smb_vol *vol)
 	return 1;
 }
 
-static struct TCP_Server_Info *
+struct TCP_Server_Info *
 cifs_find_tcp_session(struct smb_vol *vol)
 {
 	struct TCP_Server_Info *server;

fs/cifs/dfs_cache.c

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * DFS referral cache routines
+ *
+ * Copyright (c) 2018 Paulo Alcantara <palcantara@suse.de>
+ */
+
+#include <linux/rcupdate.h>
+#include <linux/rculist.h>
+#include <linux/jhash.h>
+#include <linux/ktime.h>
+#include <linux/slab.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 "dfs_cache.h"
+
+#define DFS_CACHE_HTABLE_SIZE 32
+#define DFS_CACHE_MAX_ENTRIES 64
+
+#define IS_INTERLINK_SET(v) ((v) & (DFSREF_REFERRAL_SERVER | \
+				    DFSREF_STORAGE_SERVER))
+
+struct dfs_cache_tgt {
+	char *t_name;
+	struct list_head t_list;
+};
+
+struct dfs_cache_entry {
+	struct hlist_node ce_hlist;
+	const char *ce_path;
+	int ce_ttl;
+	int ce_srvtype;
+	int ce_flags;
+	struct timespec64 ce_etime;
+	int ce_path_consumed;
+	int ce_numtgts;
+	struct list_head ce_tlist;
+	struct dfs_cache_tgt *ce_tgthint;
+	struct rcu_head ce_rcu;
+};
+
+static struct kmem_cache *dfs_cache_slab __read_mostly;
+
+struct dfs_cache_vol_info {
+	char *vi_fullpath;
+	struct smb_vol vi_vol;
+	struct list_head vi_list;
+};
+
+struct dfs_cache {
+	struct mutex dc_lock;
+	struct nls_table *dc_nlsc;
+	struct list_head dc_vol_list;
+	int dc_ttl;
+	struct delayed_work dc_refresh;
+};
+
+static struct dfs_cache dfs_cache;
+
+/*
+ * Number of entries in the cache
+ */
+static size_t dfs_cache_count;
+
+static DEFINE_MUTEX(dfs_cache_list_lock);
+static struct hlist_head dfs_cache_htable[DFS_CACHE_HTABLE_SIZE];
+
+static void refresh_cache_worker(struct work_struct *work);
+
+static inline bool is_path_valid(const char *path)
+{
+	return path && (strchr(path + 1, '\\') || strchr(path + 1, '/'));
+}
+
+static inline int get_normalized_path(const char *path, char **npath)
+{
+	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 dfs_cache_entry *ce)
+{
+	struct timespec64 ts;
+
+	ts = current_kernel_time64();
+	return timespec64_compare(&ts, &ce->ce_etime) >= 0;
+}
+
+static inline void free_tgts(struct dfs_cache_entry *ce)
+{
+	struct dfs_cache_tgt *t, *n;
+
+	list_for_each_entry_safe(t, n, &ce->ce_tlist, t_list) {
+		list_del(&t->t_list);
+		kfree(t->t_name);
+		kfree(t);
+	}
+}
+
+static void free_cache_entry(struct rcu_head *rcu)
+{
+	struct dfs_cache_entry *ce = container_of(rcu, struct dfs_cache_entry,
+						  ce_rcu);
+	kmem_cache_free(dfs_cache_slab, ce);
+}
+
+static inline void flush_cache_ent(struct dfs_cache_entry *ce)
+{
+	if (hlist_unhashed(&ce->ce_hlist))
+		return;
+
+	hlist_del_init_rcu(&ce->ce_hlist);
+	kfree(ce->ce_path);
+	free_tgts(ce);
+	dfs_cache_count--;
+	call_rcu(&ce->ce_rcu, free_cache_entry);
+}
+
+static void flush_cache_ents(void)
+{
+	int i;
+
+	rcu_read_lock();
+	for (i = 0; i < DFS_CACHE_HTABLE_SIZE; i++) {
+		struct hlist_head *l = &dfs_cache_htable[i];
+		struct dfs_cache_entry *ce;
+
+		hlist_for_each_entry_rcu(ce, l, ce_hlist)
+			flush_cache_ent(ce);
+	}
+	rcu_read_unlock();
+}
+
+/*
+ * dfs cache /proc file
+ */
+static int dfscache_proc_show(struct seq_file *m, void *v)
+{
+	int bucket;
+	struct dfs_cache_entry *ce;
+	struct dfs_cache_tgt *t;
+
+	seq_puts(m, "DFS cache\n---------\n");
+
+	mutex_lock(&dfs_cache_list_lock);
+
+	rcu_read_lock();
+	hash_for_each_rcu(dfs_cache_htable, bucket, ce, ce_hlist) {
+		seq_printf(m,
+			   "cache entry: path=%s,type=%s,ttl=%d,etime=%ld,"
+			   "interlink=%s,path_consumed=%d,expired=%s\n",
+			   ce->ce_path,
+			   ce->ce_srvtype == DFS_TYPE_ROOT ? "root" : "link",
+			   ce->ce_ttl, ce->ce_etime.tv_nsec,
+			   IS_INTERLINK_SET(ce->ce_flags) ? "yes" : "no",
+			   ce->ce_path_consumed,
+			   cache_entry_expired(ce) ? "yes" : "no");
+
+		list_for_each_entry(t, &ce->ce_tlist, t_list) {
+			seq_printf(m, "  %s%s\n",
+				   t->t_name,
+				   ce->ce_tgthint == t ? " (target hint)" : "");
+		}
+
+	}
+	rcu_read_unlock();
+
+	mutex_unlock(&dfs_cache_list_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");
+	mutex_lock(&dfs_cache_list_lock);
+	flush_cache_ents();
+	mutex_unlock(&dfs_cache_list_lock);
+
+	return count;
+}
+
+static int dfscache_proc_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, dfscache_proc_show, NULL);
+}
+
+const struct file_operations dfscache_proc_fops = {
+	.open		= dfscache_proc_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+	.write		= dfscache_proc_write,
+};
+
+#ifdef CONFIG_CIFS_DEBUG2
+static inline void dump_tgts(const struct dfs_cache_entry *ce)
+{
+	struct dfs_cache_tgt *t;
+
+	cifs_dbg(FYI, "target list:\n");
+	list_for_each_entry(t, &ce->ce_tlist, t_list) {
+		cifs_dbg(FYI, "  %s%s\n", t->t_name,
+			 ce->ce_tgthint == t ? " (target hint)" : "");
+	}
+}
+
+static inline void dump_ce(const struct dfs_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->ce_path,
+		 ce->ce_srvtype == DFS_TYPE_ROOT ? "root" : "link", ce->ce_ttl,
+		 ce->ce_etime.tv_nsec,
+		 IS_INTERLINK_SET(ce->ce_flags) ? "yes" : "no",
+		 ce->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 i;
+
+	dfs_cache_slab = kmem_cache_create("cifs_dfs_cache",
+					   sizeof(struct dfs_cache_entry), 0,
+					   SLAB_HWCACHE_ALIGN, NULL);
+	if (!dfs_cache_slab)
+		return -ENOMEM;
+
+	for (i = 0; i < DFS_CACHE_HTABLE_SIZE; i++)
+		INIT_HLIST_HEAD(&dfs_cache_htable[i]);
+
+	INIT_LIST_HEAD(&dfs_cache.dc_vol_list);
+	mutex_init(&dfs_cache.dc_lock);
+	INIT_DELAYED_WORK(&dfs_cache.dc_refresh, refresh_cache_worker);
+	dfs_cache.dc_ttl = -1;
+	dfs_cache.dc_nlsc = load_nls_default();
+
+	cifs_dbg(FYI, "%s: initialized DFS referral cache\n", __func__);
+	return 0;
+}
+
+static inline unsigned int cache_entry_hash(const void *data, int size)
+{
+	unsigned int h;
+
+	h = jhash(data, size, 0);
+	return h & (DFS_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 dfs_cache_entry *ce)
+{
+	struct dfs_cache_tgt *t = ce->ce_tgthint;
+
+	return t ? 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,
+	};
+
+	return timespec64_add(current_kernel_time64(), ts);
+}
+
+/* Allocate a new DFS target */
+static inline struct dfs_cache_tgt *alloc_tgt(const char *name)
+{
+	struct dfs_cache_tgt *t;
+
+	t = kmalloc(sizeof(*t), GFP_KERNEL);
+	if (!t)
+		return ERR_PTR(-ENOMEM);
+	t->t_name = kstrndup(name, strlen(name), GFP_KERNEL);
+	if (!t->t_name) {
+		kfree(t);
+		return ERR_PTR(-ENOMEM);
+	}
+	INIT_LIST_HEAD(&t->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 dfs_cache_entry *ce, const char *tgthint)
+{
+	int i;
+
+	ce->ce_ttl = refs[0].ttl;
+	ce->ce_etime = get_expire_time(ce->ce_ttl);
+	ce->ce_srvtype = refs[0].server_type;
+	ce->ce_flags = refs[0].ref_flag;
+	ce->ce_path_consumed = refs[0].path_consumed;
+
+	for (i = 0; i < numrefs; i++) {
+		struct dfs_cache_tgt *t;
+
+		t = alloc_tgt(refs[i].node_name);
+		if (IS_ERR(t)) {
+			free_tgts(ce);
+			return PTR_ERR(t);
+		}
+		if (tgthint && !strcasecmp(t->t_name, tgthint)) {
+			list_add(&t->t_list, &ce->ce_tlist);
+			tgthint = NULL;
+		} else {
+			list_add_tail(&t->t_list, &ce->ce_tlist);
+		}
+		ce->ce_numtgts++;
+	}
+
+	ce->ce_tgthint = list_first_entry_or_null(&ce->ce_tlist,
+						  struct dfs_cache_tgt, t_list);
+
+	return 0;
+}
+
+/* Allocate a new cache entry */
+static struct dfs_cache_entry *
+alloc_cache_entry(const char *path, const struct dfs_info3_param *refs,
+		  int numrefs)
+{
+	struct dfs_cache_entry *ce;
+	int rc;
+
+	ce = kmem_cache_zalloc(dfs_cache_slab, GFP_KERNEL);
+	if (!ce)
+		return ERR_PTR(-ENOMEM);
+
+	ce->ce_path = kstrdup_const(path, GFP_KERNEL);
+	if (!ce->ce_path) {
+		kfree(ce);
+		return ERR_PTR(-ENOMEM);
+	}
+	INIT_HLIST_NODE(&ce->ce_hlist);
+	INIT_LIST_HEAD(&ce->ce_tlist);
+
+	rc = copy_ref_data(refs, numrefs, ce, NULL);
+	if (rc) {
+		kfree(ce->ce_path);
+		kfree(ce);
+		ce = ERR_PTR(rc);
+	}
+	return ce;
+}
+
+static void remove_oldest_entry(void)
+{
+	int bucket;
+	struct dfs_cache_entry *ce;
+	struct dfs_cache_entry *to_del = NULL;
+
+	rcu_read_lock();
+	hash_for_each_rcu(dfs_cache_htable, bucket, ce, ce_hlist) {
+		if (!to_del || timespec64_compare(&ce->ce_etime,
+						  &to_del->ce_etime) < 0)
+			to_del = ce;
+	}
+	if (!to_del) {
+		cifs_dbg(FYI, "%s: no entry to remove", __func__);
+		goto out;
+	}
+	cifs_dbg(FYI, "%s: removing entry", __func__);
+	dump_ce(to_del);
+	flush_cache_ent(to_del);
+out:
+	rcu_read_unlock();
+}
+
+/* Add a new DFS cache entry */
+static inline struct dfs_cache_entry *
+add_cache_entry(unsigned int hash, const char *path,
+		const struct dfs_info3_param *refs, int numrefs)
+{
+	struct dfs_cache_entry *ce;
+
+	ce = alloc_cache_entry(path, refs, numrefs);
+	if (IS_ERR(ce))
+		return ce;
+
+	hlist_add_head_rcu(&ce->ce_hlist, &dfs_cache_htable[hash]);
+
+	mutex_lock(&dfs_cache.dc_lock);
+	if (dfs_cache.dc_ttl < 0) {
+		dfs_cache.dc_ttl = ce->ce_ttl;
+		queue_delayed_work(cifsiod_wq, &dfs_cache.dc_refresh,
+				   dfs_cache.dc_ttl * HZ);
+	} else {
+		dfs_cache.dc_ttl = min_t(int, dfs_cache.dc_ttl, ce->ce_ttl);
+		mod_delayed_work(cifsiod_wq, &dfs_cache.dc_refresh,
+				 dfs_cache.dc_ttl * HZ);
+	}
+	mutex_unlock(&dfs_cache.dc_lock);
+
+	return ce;
+}
+
+static struct dfs_cache_entry *__find_cache_entry(unsigned int hash,
+						  const char *path)
+{
+	struct dfs_cache_entry *ce;
+	bool found = false;
+
+	rcu_read_lock();
+	hlist_for_each_entry_rcu(ce, &dfs_cache_htable[hash], ce_hlist) {
+		if (!strcasecmp(path, ce->ce_path)) {
+#ifdef CONFIG_CIFS_DEBUG2
+			char *name = get_tgt_name(ce);
+
+			if (unlikely(IS_ERR(name))) {
+				rcu_read_unlock();
+				return ERR_CAST(name);
+			}
+			cifs_dbg(FYI, "%s: cache hit\n", __func__);
+			cifs_dbg(FYI, "%s: target hint: %s\n", __func__, name);
+#endif
+			found = true;
+			break;
+		}
+	}
+	rcu_read_unlock();
+	return found ? ce : ERR_PTR(-ENOENT);
+}
+
+/*
+ * Find a DFS cache entry in hash table and optionally check prefix path against
+ * @path.
+ * Use whole path components in the match.
+ * Return ERR_PTR(-ENOENT) if the entry is not found.
+ */
+static inline struct dfs_cache_entry *find_cache_entry(const char *path,
+						       unsigned int *hash)
+{
+	*hash = cache_entry_hash(path, strlen(path));
+	return __find_cache_entry(*hash, path);
+}
+
+static inline void destroy_slab_cache(void)
+{
+	rcu_barrier();
+	kmem_cache_destroy(dfs_cache_slab);
+}
+
+static inline void free_vol(struct dfs_cache_vol_info *vi)
+{
+	list_del(&vi->vi_list);
+	kfree(vi->vi_fullpath);
+	cifs_cleanup_volume_info_contents(&vi->vi_vol);
+	kfree(vi);
+}
+
+static inline void free_vol_list(void)
+{
+	struct dfs_cache_vol_info *vi, *nvi;
+
+	list_for_each_entry_safe(vi, nvi, &dfs_cache.dc_vol_list, vi_list)
+		free_vol(vi);
+}
+
+/**
+ * dfs_cache_destroy - destroy DFS referral cache
+ */
+void dfs_cache_destroy(void)
+{
+	cancel_delayed_work_sync(&dfs_cache.dc_refresh);
+	unload_nls(dfs_cache.dc_nlsc);
+	free_vol_list();
+	mutex_destroy(&dfs_cache.dc_lock);
+
+	flush_cache_ents();
+	destroy_slab_cache();
+	mutex_destroy(&dfs_cache_list_lock);
+
+	cifs_dbg(FYI, "%s: destroyed DFS referral cache\n", __func__);
+}
+
+static inline struct dfs_cache_entry *
+__update_cache_entry(const char *path, const struct dfs_info3_param *refs,
+		     int numrefs)
+{
+	int rc;
+	unsigned int h;
+	struct dfs_cache_entry *ce;
+	char *s, *th = NULL;
+
+	ce = find_cache_entry(path, &h);
+	if (IS_ERR(ce))
+		return ce;
+
+	if (ce->ce_tgthint) {
+		s = ce->ce_tgthint->t_name;
+		th = kstrndup(s, strlen(s), GFP_KERNEL);
+		if (!th)
+			return ERR_PTR(-ENOMEM);
+	}
+
+	free_tgts(ce);
+	ce->ce_numtgts = 0;
+
+	rc = copy_ref_data(refs, numrefs, ce, th);
+	kfree(th);
+
+	if (rc)
+		ce = ERR_PTR(rc);
+
+	return ce;
+}
+
+/* Update an expired cache entry by getting a new DFS referral from server */
+static struct dfs_cache_entry *
+update_cache_entry(const unsigned int xid, struct cifs_ses *ses,
+		   const struct nls_table *nls_codepage, int remap,
+		   const char *path, struct dfs_cache_entry *ce)
+{
+	int rc;
+	struct dfs_info3_param *refs = NULL;
+	int numrefs = 0;
+
+	cifs_dbg(FYI, "%s: update expired cache entry\n", __func__);
+	/*
+	 * Check if caller provided enough parameters to update an expired
+	 * entry.
+	 */
+	if (!ses || !ses->server || !ses->server->ops->get_dfs_refer)
+		return ERR_PTR(-ETIME);
+	if (unlikely(!nls_codepage))
+		return ERR_PTR(-ETIME);
+
+	cifs_dbg(FYI, "%s: DFS referral request for %s\n", __func__, path);
+
+	rc = ses->server->ops->get_dfs_refer(xid, ses, path, &refs, &numrefs,
+					     nls_codepage, remap);
+	if (rc)
+		ce = ERR_PTR(rc);
+	else
+		ce = __update_cache_entry(path, refs, numrefs);
+
+	dump_refs(refs, numrefs);
+	free_dfs_info_array(refs, numrefs);
+
+	return ce;
+}
+
+/*
+ * 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 struct dfs_cache_entry *
+do_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 h;
+	struct dfs_cache_entry *ce;
+	struct dfs_info3_param *nrefs;
+	int numnrefs;
+
+	cifs_dbg(FYI, "%s: search path: %s\n", __func__, path);
+
+	ce = find_cache_entry(path, &h);
+	if (IS_ERR(ce)) {
+		cifs_dbg(FYI, "%s: cache miss\n", __func__);
+		/*
+		 * If @noreq is set, no requests will be sent to the server for
+		 * either updating or getting a new DFS referral.
+		 */
+		if (noreq)
+			return ce;
+		/*
+		 * No cache entry was found, so check for valid parameters that
+		 * will be required to get a new DFS referral and then create a
+		 * new cache entry.
+		 */
+		if (!ses || !ses->server || !ses->server->ops->get_dfs_refer) {
+			ce = ERR_PTR(-EOPNOTSUPP);
+			return ce;
+		}
+		if (unlikely(!nls_codepage)) {
+			ce = ERR_PTR(-EINVAL);
+			return ce;
+		}
+
+		nrefs = NULL;
+		numnrefs = 0;
+
+		cifs_dbg(FYI, "%s: DFS referral request for %s\n", __func__,
+			 path);
+
+		rc = ses->server->ops->get_dfs_refer(xid, ses, path, &nrefs,
+						     &numnrefs, nls_codepage,
+						     remap);
+		if (rc) {
+			ce = ERR_PTR(rc);
+			return ce;
+		}
+
+		dump_refs(nrefs, numnrefs);
+
+		cifs_dbg(FYI, "%s: new cache entry\n", __func__);
+
+		if (dfs_cache_count >= DFS_CACHE_MAX_ENTRIES) {
+			cifs_dbg(FYI, "%s: reached max cache size (%d)",
+				 __func__, DFS_CACHE_MAX_ENTRIES);
+			remove_oldest_entry();
+		}
+		ce = add_cache_entry(h, path, nrefs, numnrefs);
+		free_dfs_info_array(nrefs, numnrefs);
+
+		if (IS_ERR(ce))
+			return ce;
+
+		dfs_cache_count++;
+	}
+
+	dump_ce(ce);
+
+	/* Just return the found cache entry in case @noreq is set */
+	if (noreq)
+		return ce;
+
+	if (cache_entry_expired(ce)) {
+		cifs_dbg(FYI, "%s: expired cache entry\n", __func__);
+		ce = update_cache_entry(xid, ses, nls_codepage, remap, path,
+					ce);
+		if (IS_ERR(ce)) {
+			cifs_dbg(FYI, "%s: failed to update expired entry\n",
+				 __func__);
+		}
+	}
+	return ce;
+}
+
+/* Set up a new DFS referral from a given cache entry */
+static int setup_ref(const char *path, const struct dfs_cache_entry *ce,
+		     struct dfs_info3_param *ref, const char *tgt)
+{
+	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_KERNEL);
+	if (!ref->path_name)
+		return -ENOMEM;
+
+	ref->path_consumed = ce->ce_path_consumed;
+
+	ref->node_name = kstrndup(tgt, strlen(tgt), GFP_KERNEL);
+	if (!ref->node_name) {
+		rc = -ENOMEM;
+		goto err_free_path;
+	}
+
+	ref->ttl = ce->ce_ttl;
+	ref->server_type = ce->ce_srvtype;
+	ref->ref_flag = ce->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_tgt_list(const struct dfs_cache_entry *ce,
+			struct dfs_cache_tgt_list *tl)
+{
+	int rc;
+	struct list_head *head = &tl->tl_list;
+	struct dfs_cache_tgt *t;
+	struct dfs_cache_tgt_iterator *it, *nit;
+
+	memset(tl, 0, sizeof(*tl));
+	INIT_LIST_HEAD(head);
+
+	list_for_each_entry(t, &ce->ce_tlist, t_list) {
+		it = kzalloc(sizeof(*it), GFP_KERNEL);
+		if (!it) {
+			rc = -ENOMEM;
+			goto err_free_it;
+		}
+
+		it->it_name = kstrndup(t->t_name, strlen(t->t_name),
+				       GFP_KERNEL);
+		if (!it->it_name) {
+			rc = -ENOMEM;
+			goto err_free_it;
+		}
+
+		if (ce->ce_tgthint == t)
+			list_add(&it->it_list, head);
+		else
+			list_add_tail(&it->it_list, head);
+	}
+	tl->tl_numtgts = ce->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 dfs_cache_entry *ce;
+
+	if (unlikely(!is_path_valid(path)))
+		return -EINVAL;
+
+	rc = get_normalized_path(path, &npath);
+	if (rc)
+		return rc;
+
+	mutex_lock(&dfs_cache_list_lock);
+	ce = do_dfs_cache_find(xid, ses, nls_codepage, remap, npath, false);
+	if (!IS_ERR(ce)) {
+		if (ref)
+			rc = setup_ref(path, ce, ref, get_tgt_name(ce));
+		else
+			rc = 0;
+		if (!rc && tgt_list)
+			rc = get_tgt_list(ce, tgt_list);
+	} else {
+		rc = PTR_ERR(ce);
+	}
+	mutex_unlock(&dfs_cache_list_lock);
+	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 dfs_cache_entry *ce;
+
+	if (unlikely(!is_path_valid(path)))
+		return -EINVAL;
+
+	rc = get_normalized_path(path, &npath);
+	if (rc)
+		return rc;
+
+	mutex_lock(&dfs_cache_list_lock);
+	ce = do_dfs_cache_find(0, NULL, NULL, 0, npath, true);
+	if (IS_ERR(ce)) {
+		rc = PTR_ERR(ce);
+		goto out;
+	}
+
+	if (ref)
+		rc = setup_ref(path, ce, ref, get_tgt_name(ce));
+	else
+		rc = 0;
+	if (!rc && tgt_list)
+		rc = get_tgt_list(ce, tgt_list);
+out:
+	mutex_unlock(&dfs_cache_list_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 dfs_cache_entry *ce;
+	struct dfs_cache_tgt *t;
+
+	if (unlikely(!is_path_valid(path)))
+		return -EINVAL;
+
+	rc = get_normalized_path(path, &npath);
+	if (rc)
+		return rc;
+
+	cifs_dbg(FYI, "%s: path: %s\n", __func__, npath);
+
+	mutex_lock(&dfs_cache_list_lock);
+	ce = do_dfs_cache_find(xid, ses, nls_codepage, remap, npath, false);
+	if (IS_ERR(ce)) {
+		rc = PTR_ERR(ce);
+		goto out;
+	}
+
+	rc = 0;
+
+	t = ce->ce_tgthint;
+
+	if (likely(!strcasecmp(it->it_name, t->t_name)))
+		goto out;
+
+	list_for_each_entry(t, &ce->ce_tlist, t_list) {
+		if (!strcasecmp(t->t_name, it->it_name)) {
+			ce->ce_tgthint = t;
+			cifs_dbg(FYI, "%s: new target hint: %s\n", __func__,
+				 it->it_name);
+			break;
+		}
+	}
+
+out:
+	mutex_unlock(&dfs_cache_list_lock);
+	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 dfs_cache_entry *ce;
+	struct dfs_cache_tgt *t;
+
+	if (unlikely(!is_path_valid(path)) || !it)
+		return -EINVAL;
+
+	rc = get_normalized_path(path, &npath);
+	if (rc)
+		return rc;
+
+	cifs_dbg(FYI, "%s: path: %s\n", __func__, npath);
+
+	mutex_lock(&dfs_cache_list_lock);
+
+	ce = do_dfs_cache_find(0, NULL, NULL, 0, npath, true);
+	if (IS_ERR(ce)) {
+		rc = PTR_ERR(ce);
+		goto out;
+	}
+
+	rc = 0;
+
+	t = ce->ce_tgthint;
+
+	if (unlikely(!strcasecmp(it->it_name, t->t_name)))
+		goto out;
+
+	list_for_each_entry(t, &ce->ce_tlist, t_list) {
+		if (!strcasecmp(t->t_name, it->it_name)) {
+			ce->ce_tgthint = t;
+			cifs_dbg(FYI, "%s: new target hint: %s\n", __func__,
+				 it->it_name);
+			break;
+		}
+	}
+
+out:
+	mutex_unlock(&dfs_cache_list_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 dfs_cache_entry *ce;
+	unsigned int h;
+
+	if (!it || !ref)
+		return -EINVAL;
+	if (unlikely(!is_path_valid(path)))
+		return -EINVAL;
+
+	rc = get_normalized_path(path, &npath);
+	if (rc)
+		return rc;
+
+	cifs_dbg(FYI, "%s: path: %s\n", __func__, npath);
+
+	mutex_lock(&dfs_cache_list_lock);
+
+	ce = find_cache_entry(npath, &h);
+	if (IS_ERR(ce)) {
+		rc = PTR_ERR(ce);
+		goto out;
+	}
+
+	cifs_dbg(FYI, "%s: target name: %s\n", __func__, it->it_name);
+
+	rc = setup_ref(path, ce, ref, it->it_name);
+
+out:
+	mutex_unlock(&dfs_cache_list_lock);
+	free_normalized_path(path, npath);
+	return rc;
+}
+
+static int dup_vol(struct smb_vol *vol, struct smb_vol *new)
+{
+	memcpy(new, vol, sizeof(*new));
+
+	if (vol->username) {
+		new->username = kstrndup(vol->username, strlen(vol->username),
+					GFP_KERNEL);
+		if (!new->username)
+			return -ENOMEM;
+	}
+	if (vol->password) {
+		new->password = kstrndup(vol->password, strlen(vol->password),
+					 GFP_KERNEL);
+		if (!new->password)
+			goto err_free_username;
+	}
+	if (vol->UNC) {
+		cifs_dbg(FYI, "%s: vol->UNC: %s\n", __func__, vol->UNC);
+		new->UNC = kstrndup(vol->UNC, strlen(vol->UNC), GFP_KERNEL);
+		if (!new->UNC)
+			goto err_free_password;
+	}
+	if (vol->domainname) {
+		new->domainname = kstrndup(vol->domainname,
+					  strlen(vol->domainname), GFP_KERNEL);
+		if (!new->domainname)
+			goto err_free_unc;
+	}
+	if (vol->iocharset) {
+		new->iocharset = kstrndup(vol->iocharset,
+					  strlen(vol->iocharset), GFP_KERNEL);
+		if (!new->iocharset)
+			goto err_free_domainname;
+	}
+	if (vol->prepath) {
+		cifs_dbg(FYI, "%s: vol->prepath: %s\n", __func__, vol->prepath);
+		new->prepath = kstrndup(vol->prepath, strlen(vol->prepath),
+					GFP_KERNEL);
+		if (!new->prepath)
+			goto err_free_iocharset;
+	}
+
+	return 0;
+
+err_free_iocharset:
+	kfree(new->iocharset);
+err_free_domainname:
+	kfree(new->domainname);
+err_free_unc:
+	kfree(new->UNC);
+err_free_password:
+	kfree(new->password);
+err_free_username:
+	kfree(new->username);
+	kfree(new);
+	return -ENOMEM;
+}
+
+/**
+ * dfs_cache_add_vol - add a cifs volume during mount() that will be handled by
+ * DFS cache refresh worker.
+ *
+ * @vol: cifs volume.
+ * @fullpath: origin full path.
+ *
+ * Return zero if volume was set up correctly, otherwise non-zero.
+ */
+int dfs_cache_add_vol(struct smb_vol *vol, const char *fullpath)
+{
+	int rc;
+	struct dfs_cache_vol_info *vi;
+
+	if (!vol || !fullpath)
+		return -EINVAL;
+
+	cifs_dbg(FYI, "%s: fullpath: %s\n", __func__, fullpath);
+
+	vi = kzalloc(sizeof(*vi), GFP_KERNEL);
+	if (!vi)
+		return -ENOMEM;
+
+	vi->vi_fullpath = kstrndup(fullpath, strlen(fullpath), GFP_KERNEL);
+	if (!vi->vi_fullpath) {
+		rc = -ENOMEM;
+		goto err_free_vi;
+	}
+
+	rc = dup_vol(vol, &vi->vi_vol);
+	if (rc)
+		goto err_free_fullpath;
+
+	mutex_lock(&dfs_cache.dc_lock);
+	list_add_tail(&vi->vi_list, &dfs_cache.dc_vol_list);
+	mutex_unlock(&dfs_cache.dc_lock);
+	return 0;
+
+err_free_fullpath:
+	kfree(vi->vi_fullpath);
+err_free_vi:
+	kfree(vi);
+	return rc;
+}
+
+static inline struct dfs_cache_vol_info *find_vol(const char *fullpath)
+{
+	struct dfs_cache_vol_info *vi;
+
+	list_for_each_entry(vi, &dfs_cache.dc_vol_list, vi_list) {
+		cifs_dbg(FYI, "%s: vi->vi_fullpath: %s\n", __func__,
+			 vi->vi_fullpath);
+		if (!strcasecmp(vi->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)
+{
+	int rc;
+	struct dfs_cache_vol_info *vi;
+
+	if (!fullpath || !server)
+		return -EINVAL;
+
+	cifs_dbg(FYI, "%s: fullpath: %s\n", __func__, fullpath);
+
+	mutex_lock(&dfs_cache.dc_lock);
+
+	vi = find_vol(fullpath);
+	if (IS_ERR(vi)) {
+		rc = PTR_ERR(vi);
+		goto out;
+	}
+
+	cifs_dbg(FYI, "%s: updating volume info\n", __func__);
+	memcpy(&vi->vi_vol.dstaddr, &server->dstaddr,
+	       sizeof(vi->vi_vol.dstaddr));
+	rc = 0;
+
+out:
+	mutex_unlock(&dfs_cache.dc_lock);
+	return rc;
+}
+
+/**
+ * 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 dfs_cache_vol_info *vi;
+
+	if (!fullpath || !*fullpath)
+		return;
+
+	cifs_dbg(FYI, "%s: fullpath: %s\n", __func__, fullpath);
+
+	mutex_lock(&dfs_cache.dc_lock);
+	vi = find_vol(fullpath);
+	if (!IS_ERR(vi))
+		free_vol(vi);
+	mutex_unlock(&dfs_cache.dc_lock);
+}
+
+/* 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);
+}
+
+/* Refresh DFS cache entry from a given tcon */
+static void do_refresh_tcon(struct dfs_cache *dc, struct cifs_tcon *tcon)
+{
+	int rc = 0;
+	unsigned int xid;
+	char *path, *npath;
+	unsigned int h;
+	struct dfs_cache_entry *ce;
+	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;
+
+	mutex_lock(&dfs_cache_list_lock);
+	ce = find_cache_entry(npath, &h);
+	mutex_unlock(&dfs_cache_list_lock);
+
+	if (IS_ERR(ce)) {
+		rc = PTR_ERR(ce);
+		goto out;
+	}
+
+	if (!cache_entry_expired(ce))
+		goto out;
+
+	if (unlikely(!tcon->ses->server->ops->get_dfs_refer)) {
+		rc = -EOPNOTSUPP;
+	} else {
+		rc = tcon->ses->server->ops->get_dfs_refer(xid, tcon->ses, path,
+							   &refs, &numrefs,
+							   dc->dc_nlsc,
+							   tcon->remap);
+		if (!rc) {
+			mutex_lock(&dfs_cache_list_lock);
+			ce = __update_cache_entry(npath, refs, numrefs);
+			mutex_unlock(&dfs_cache_list_lock);
+			dump_refs(refs, numrefs);
+			free_dfs_info_array(refs, numrefs);
+			if (IS_ERR(ce))
+				rc = PTR_ERR(ce);
+		}
+	}
+	if (rc)
+		cifs_dbg(FYI, "%s: failed to update expired entry\n", __func__);
+out:
+	free_xid(xid);
+	free_normalized_path(path, npath);
+}
+
+/*
+ * Worker that will refresh DFS cache based on lowest TTL value from a DFS
+ * referral.
+ *
+ * FIXME: ensure that all requests are sent to DFS root for refreshing the
+ * cache.
+ */
+static void refresh_cache_worker(struct work_struct *work)
+{
+	struct dfs_cache *dc = container_of(work, struct dfs_cache,
+					    dc_refresh.work);
+	struct dfs_cache_vol_info *vi;
+	struct TCP_Server_Info *server;
+	LIST_HEAD(list);
+	struct cifs_tcon *tcon, *ntcon;
+
+	mutex_lock(&dc->dc_lock);
+
+	list_for_each_entry(vi, &dc->dc_vol_list, vi_list) {
+		server = cifs_find_tcp_session(&vi->vi_vol);
+		if (IS_ERR_OR_NULL(server))
+			continue;
+		if (server->tcpStatus != CifsGood)
+			goto next;
+		get_tcons(server, &list);
+		list_for_each_entry_safe(tcon, ntcon, &list, ulist) {
+			do_refresh_tcon(dc, tcon);
+			list_del_init(&tcon->ulist);
+			cifs_put_tcon(tcon);
+		}
+next:
+		cifs_put_tcp_session(server, 0);
+	}
+	queue_delayed_work(cifsiod_wq, &dc->dc_refresh, dc->dc_ttl * HZ);
+	mutex_unlock(&dc->dc_lock);
+}

fs/cifs/dfs_cache.h

+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * DFS referral cache routines
+ *
+ * Copyright (c) 2018 Paulo Alcantara <palcantara@suse.de>
+ */
+
+#ifndef _CIFS_DFS_CACHE_H
+#define _CIFS_DFS_CACHE_H
+
+#include <linux/nls.h>
+#include <linux/list.h>
+#include "cifsglob.h"
+
+struct dfs_cache_tgt_list {
+	int tl_numtgts;
+	struct list_head tl_list;
+};
+
+struct dfs_cache_tgt_iterator {
+	char *it_name;
+	struct list_head it_list;
+};
+
+extern int dfs_cache_init(void);
+extern void dfs_cache_destroy(void);
+extern const struct file_operations dfscache_proc_fops;
+
+extern 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);
+extern int dfs_cache_noreq_find(const char *path, struct dfs_info3_param *ref,
+				struct dfs_cache_tgt_list *tgt_list);
+extern 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);
+extern int
+dfs_cache_noreq_update_tgthint(const char *path,
+			       const struct dfs_cache_tgt_iterator *it);
+extern int dfs_cache_get_tgt_referral(const char *path,
+				      const struct dfs_cache_tgt_iterator *it,
+				      struct dfs_info3_param *ref);
+extern int dfs_cache_add_vol(struct smb_vol *vol, const char *fullpath);
+extern int dfs_cache_update_vol(const char *fullpath,
+				struct TCP_Server_Info *server);
+extern void dfs_cache_del_vol(const char *fullpath);
+
+static inline struct dfs_cache_tgt_iterator *
+dfs_cache_get_next_tgt(struct dfs_cache_tgt_list *tl,
+		       struct dfs_cache_tgt_iterator *it)
+{
+	if (!tl || list_empty(&tl->tl_list) || !it ||
+	    list_is_last(&it->it_list, &tl->tl_list))
+		return NULL;
+	return list_next_entry(it, it_list);
+}
+
+static inline struct dfs_cache_tgt_iterator *
+dfs_cache_get_tgt_iterator(struct dfs_cache_tgt_list *tl)
+{
+	if (!tl)
+		return NULL;
+	return list_first_entry_or_null(&tl->tl_list,
+					struct dfs_cache_tgt_iterator,
+					it_list);
+}
+
+static inline void dfs_cache_free_tgts(struct dfs_cache_tgt_list *tl)
+{
+	struct dfs_cache_tgt_iterator *it, *nit;
+
+	if (!tl || list_empty(&tl->tl_list))
+		return;
+	list_for_each_entry_safe(it, nit, &tl->tl_list, it_list) {
+		list_del(&it->it_list);
+		kfree(it->it_name);
+		kfree(it);
+	}
+	tl->tl_numtgts = 0;
+}
+
+static inline const char *
+dfs_cache_get_tgt_name(const struct dfs_cache_tgt_iterator *it)
+{
+	return it ? it->it_name : NULL;
+}
+
+static inline int
+dfs_cache_get_nr_tgts(const struct dfs_cache_tgt_list *tl)
+{
+	return tl ? tl->tl_numtgts : 0;
+}
+
+#endif /* _CIFS_DFS_CACHE_H */