[PATCH 0/7] DFS fixes

[PATCH 0/7] DFS fixes

[Paulo Alcantara]

Hi Steve,

Follow some fixes, cleanups and documentation for DFS.

All DFS failover tests passed with this series in our local buildbot.

Paulo Alcantara (6):
  cifs: reduce number of referral requests in DFS link lookups
  cifs: rename reconn_inval_dfs_target()
  cifs: handle empty list of targets in cifs_reconnect()
  cifs: handle RESP_GET_DFS_REFERRAL.PathConsumed in reconnect
  cifs: only update prefix path of DFS links in cifs_tree_connect()
  cifs: document and cleanup dfs mount

Stefan Metzmacher (1):
  cifs: merge __{cifs,smb2}_reconnect[_tcon]() into cifs_tree_connect()

 fs/cifs/cifsproto.h |   6 +-
 fs/cifs/cifssmb.c   | 112 +---------
 fs/cifs/connect.c   | 504 ++++++++++++++++++++++++++------------------
 fs/cifs/dfs_cache.c | 136 +++++++++---
 fs/cifs/dfs_cache.h |   7 +-
 fs/cifs/misc.c      |   7 +-
 fs/cifs/smb2pdu.c   | 113 +---------
 7 files changed, 428 insertions(+), 457 deletions(-)

-- 
2.27.0

[PATCH 1/7] cifs: merge __{cifs,smb2}_reconnect[_tcon]() into cifs_tree_connect()

[Paulo Alcantara]

From: Stefan Metzmacher <metze@samba.org>

They were identical execpt to CIFSTCon() vs. SMB2_tcon().
These are also available via ops->tree_connect().

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
---
 fs/cifs/cifsproto.h |   3 ++
 fs/cifs/cifssmb.c   | 112 +------------------------------------------
 fs/cifs/connect.c   | 100 +++++++++++++++++++++++++++++++++++++++
 fs/cifs/smb2pdu.c   | 113 +-------------------------------------------
 4 files changed, 105 insertions(+), 223 deletions(-)

diff --git a/fs/cifs/cifsproto.h b/fs/cifs/cifsproto.h
index 7a836ec0438e..93b018723abf 100644
--- a/fs/cifs/cifsproto.h
+++ b/fs/cifs/cifsproto.h
@@ -271,6 +271,9 @@ extern void cifs_move_llist(struct list_head *source, struct list_head *dest);
 extern void cifs_free_llist(struct list_head *llist);
 extern void cifs_del_lock_waiters(struct cifsLockInfo *lock);
 
+extern int cifs_tree_connect(const unsigned int xid, struct cifs_tcon *tcon,
+			     const struct nls_table *nlsc);
+
 extern int cifs_negotiate_protocol(const unsigned int xid,
 				   struct cifs_ses *ses);
 extern int cifs_setup_session(const unsigned int xid, struct cifs_ses *ses,
diff --git a/fs/cifs/cifssmb.c b/fs/cifs/cifssmb.c
index bf41ee048396..a6ea7e7b18cd 100644
--- a/fs/cifs/cifssmb.c
+++ b/fs/cifs/cifssmb.c
@@ -124,116 +124,6 @@ cifs_mark_open_files_invalid(struct cifs_tcon *tcon)
 	 */
 }
 
-#ifdef CONFIG_CIFS_DFS_UPCALL
-static int __cifs_reconnect_tcon(const struct nls_table *nlsc,
-				 struct cifs_tcon *tcon)
-{
-	int rc;
-	struct TCP_Server_Info *server = tcon->ses->server;
-	struct dfs_cache_tgt_list tl;
-	struct dfs_cache_tgt_iterator *it = NULL;
-	char *tree;
-	const char *tcp_host;
-	size_t tcp_host_len;
-	const char *dfs_host;
-	size_t dfs_host_len;
-
-	tree = kzalloc(MAX_TREE_SIZE, GFP_KERNEL);
-	if (!tree)
-		return -ENOMEM;
-
-	if (!tcon->dfs_path) {
-		if (tcon->ipc) {
-			scnprintf(tree, MAX_TREE_SIZE, "\\\\%s\\IPC$",
-				  server->hostname);
-			rc = CIFSTCon(0, tcon->ses, tree, tcon, nlsc);
-		} else {
-			rc = CIFSTCon(0, tcon->ses, tcon->treeName, tcon, nlsc);
-		}
-		goto out;
-	}
-
-	rc = dfs_cache_noreq_find(tcon->dfs_path + 1, NULL, &tl);
-	if (rc)
-		goto out;
-
-	extract_unc_hostname(server->hostname, &tcp_host, &tcp_host_len);
-
-	for (it = dfs_cache_get_tgt_iterator(&tl); it;
-	     it = dfs_cache_get_next_tgt(&tl, it)) {
-		const char *share, *prefix;
-		size_t share_len, prefix_len;
-		bool target_match;
-
-		rc = dfs_cache_get_tgt_share(it, &share, &share_len, &prefix,
-					     &prefix_len);
-		if (rc) {
-			cifs_dbg(VFS, "%s: failed to parse target share %d\n",
-				 __func__, rc);
-			continue;
-		}
-
-		extract_unc_hostname(share, &dfs_host, &dfs_host_len);
-
-		if (dfs_host_len != tcp_host_len
-		    || strncasecmp(dfs_host, tcp_host, dfs_host_len) != 0) {
-			cifs_dbg(FYI, "%s: %.*s doesn't match %.*s\n",
-				 __func__,
-				 (int)dfs_host_len, dfs_host,
-				 (int)tcp_host_len, tcp_host);
-
-			rc = match_target_ip(server, dfs_host, dfs_host_len,
-					     &target_match);
-			if (rc) {
-				cifs_dbg(VFS, "%s: failed to match target ip: %d\n",
-					 __func__, rc);
-				break;
-			}
-
-			if (!target_match) {
-				cifs_dbg(FYI, "%s: skipping target\n", __func__);
-				continue;
-			}
-		}
-
-		if (tcon->ipc) {
-			scnprintf(tree, MAX_TREE_SIZE, "\\\\%.*s\\IPC$",
-				  (int)share_len, share);
-			rc = CIFSTCon(0, tcon->ses, tree, tcon, nlsc);
-		} else {
-			scnprintf(tree, MAX_TREE_SIZE, "\\%.*s", (int)share_len,
-				  share);
-			rc = CIFSTCon(0, tcon->ses, tree, tcon, nlsc);
-			if (!rc) {
-				rc = update_super_prepath(tcon, prefix,
-							  prefix_len);
-				break;
-			}
-		}
-		if (rc == -EREMOTE)
-			break;
-	}
-
-	if (!rc) {
-		if (it)
-			rc = dfs_cache_noreq_update_tgthint(tcon->dfs_path + 1,
-							    it);
-		else
-			rc = -ENOENT;
-	}
-	dfs_cache_free_tgts(&tl);
-out:
-	kfree(tree);
-	return rc;
-}
-#else
-static inline int __cifs_reconnect_tcon(const struct nls_table *nlsc,
-					struct cifs_tcon *tcon)
-{
-	return CIFSTCon(0, tcon->ses, tcon->treeName, tcon, nlsc);
-}
-#endif
-
 /* reconnect the socket, tcon, and smb session if needed */
 static int
 cifs_reconnect_tcon(struct cifs_tcon *tcon, int smb_command)
@@ -338,7 +228,7 @@ cifs_reconnect_tcon(struct cifs_tcon *tcon, int smb_command)
 	}
 
 	cifs_mark_open_files_invalid(tcon);
-	rc = __cifs_reconnect_tcon(nls_codepage, tcon);
+	rc = cifs_tree_connect(0, tcon, nls_codepage);
 	mutex_unlock(&ses->session_mutex);
 	cifs_dbg(FYI, "reconnect tcon rc = %d\n", rc);
 
diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index a61abde09ffe..5c3c65265478 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -5533,3 +5533,103 @@ cifs_prune_tlinks(struct work_struct *work)
 	queue_delayed_work(cifsiod_wq, &cifs_sb->prune_tlinks,
 				TLINK_IDLE_EXPIRE);
 }
+
+#ifdef CONFIG_CIFS_DFS_UPCALL
+int cifs_tree_connect(const unsigned int xid, struct cifs_tcon *tcon, const struct nls_table *nlsc)
+{
+	int rc;
+	struct TCP_Server_Info *server = tcon->ses->server;
+	const struct smb_version_operations *ops = server->ops;
+	struct dfs_cache_tgt_list tl;
+	struct dfs_cache_tgt_iterator *it = NULL;
+	char *tree;
+	const char *tcp_host;
+	size_t tcp_host_len;
+	const char *dfs_host;
+	size_t dfs_host_len;
+
+	tree = kzalloc(MAX_TREE_SIZE, GFP_KERNEL);
+	if (!tree)
+		return -ENOMEM;
+
+	if (!tcon->dfs_path) {
+		if (tcon->ipc) {
+			scnprintf(tree, MAX_TREE_SIZE, "\\\\%s\\IPC$", server->hostname);
+			rc = ops->tree_connect(xid, tcon->ses, tree, tcon, nlsc);
+		} else {
+			rc = ops->tree_connect(xid, tcon->ses, tcon->treeName, tcon, nlsc);
+		}
+		goto out;
+	}
+
+	rc = dfs_cache_noreq_find(tcon->dfs_path + 1, NULL, &tl);
+	if (rc)
+		goto out;
+
+	extract_unc_hostname(server->hostname, &tcp_host, &tcp_host_len);
+
+	for (it = dfs_cache_get_tgt_iterator(&tl); it; it = dfs_cache_get_next_tgt(&tl, it)) {
+		const char *share, *prefix;
+		size_t share_len, prefix_len;
+		bool target_match;
+
+		rc = dfs_cache_get_tgt_share(it, &share, &share_len, &prefix, &prefix_len);
+		if (rc) {
+			cifs_dbg(VFS, "%s: failed to parse target share %d\n",
+				 __func__, rc);
+			continue;
+		}
+
+		extract_unc_hostname(share, &dfs_host, &dfs_host_len);
+
+		if (dfs_host_len != tcp_host_len
+		    || strncasecmp(dfs_host, tcp_host, dfs_host_len) != 0) {
+			cifs_dbg(FYI, "%s: %.*s doesn't match %.*s\n", __func__, (int)dfs_host_len,
+				 dfs_host, (int)tcp_host_len, tcp_host);
+
+			rc = match_target_ip(server, dfs_host, dfs_host_len, &target_match);
+			if (rc) {
+				cifs_dbg(VFS, "%s: failed to match target ip: %d\n", __func__, rc);
+				break;
+			}
+
+			if (!target_match) {
+				cifs_dbg(FYI, "%s: skipping target\n", __func__);
+				continue;
+			}
+		}
+
+		if (tcon->ipc) {
+			scnprintf(tree, MAX_TREE_SIZE, "\\\\%s\\IPC$", share);
+			rc = ops->tree_connect(xid, tcon->ses, tree, tcon, nlsc);
+		} else {
+			scnprintf(tree, MAX_TREE_SIZE, "\\%s", share);
+			rc = ops->tree_connect(xid, tcon->ses, tree, tcon, nlsc);
+			if (!rc) {
+				rc = update_super_prepath(tcon, prefix, prefix_len);
+				break;
+			}
+		}
+		if (rc == -EREMOTE)
+			break;
+	}
+
+	if (!rc) {
+		if (it)
+			rc = dfs_cache_noreq_update_tgthint(tcon->dfs_path + 1, it);
+		else
+			rc = -ENOENT;
+	}
+	dfs_cache_free_tgts(&tl);
+out:
+	kfree(tree);
+	return rc;
+}
+#else
+int cifs_tree_connect(const unsigned int xid, struct cifs_tcon *tcon, const struct nls_table *nlsc)
+{
+	const struct smb_version_operations *ops = tcon->ses->server->ops;
+
+	return ops->tree_connect(xid, tcon->ses, tcon->treeName, tcon, nlsc);
+}
+#endif
diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
index 2f4cdd290c46..c03e5b79a969 100644
--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -152,117 +152,6 @@ smb2_hdr_assemble(struct smb2_sync_hdr *shdr, __le16 smb2_cmd,
 	return;
 }
 
-#ifdef CONFIG_CIFS_DFS_UPCALL
-static int __smb2_reconnect(const struct nls_table *nlsc,
-			    struct cifs_tcon *tcon)
-{
-	int rc;
-	struct TCP_Server_Info *server = tcon->ses->server;
-	struct dfs_cache_tgt_list tl;
-	struct dfs_cache_tgt_iterator *it = NULL;
-	char *tree;
-	const char *tcp_host;
-	size_t tcp_host_len;
-	const char *dfs_host;
-	size_t dfs_host_len;
-
-	tree = kzalloc(MAX_TREE_SIZE, GFP_KERNEL);
-	if (!tree)
-		return -ENOMEM;
-
-	if (!tcon->dfs_path) {
-		if (tcon->ipc) {
-			scnprintf(tree, MAX_TREE_SIZE, "\\\\%s\\IPC$",
-				  server->hostname);
-			rc = SMB2_tcon(0, tcon->ses, tree, tcon, nlsc);
-		} else {
-			rc = SMB2_tcon(0, tcon->ses, tcon->treeName, tcon,
-				       nlsc);
-		}
-		goto out;
-	}
-
-	rc = dfs_cache_noreq_find(tcon->dfs_path + 1, NULL, &tl);
-	if (rc)
-		goto out;
-
-	extract_unc_hostname(server->hostname, &tcp_host, &tcp_host_len);
-
-	for (it = dfs_cache_get_tgt_iterator(&tl); it;
-	     it = dfs_cache_get_next_tgt(&tl, it)) {
-		const char *share, *prefix;
-		size_t share_len, prefix_len;
-		bool target_match;
-
-		rc = dfs_cache_get_tgt_share(it, &share, &share_len, &prefix,
-					     &prefix_len);
-		if (rc) {
-			cifs_dbg(VFS, "%s: failed to parse target share %d\n",
-				 __func__, rc);
-			continue;
-		}
-
-		extract_unc_hostname(share, &dfs_host, &dfs_host_len);
-
-		if (dfs_host_len != tcp_host_len
-		    || strncasecmp(dfs_host, tcp_host, dfs_host_len) != 0) {
-			cifs_dbg(FYI, "%s: %.*s doesn't match %.*s\n",
-				 __func__,
-				 (int)dfs_host_len, dfs_host,
-				 (int)tcp_host_len, tcp_host);
-
-			rc = match_target_ip(server, dfs_host, dfs_host_len,
-					     &target_match);
-			if (rc) {
-				cifs_dbg(VFS, "%s: failed to match target ip: %d\n",
-					 __func__, rc);
-				break;
-			}
-
-			if (!target_match) {
-				cifs_dbg(FYI, "%s: skipping target\n", __func__);
-				continue;
-			}
-		}
-
-		if (tcon->ipc) {
-			scnprintf(tree, MAX_TREE_SIZE, "\\\\%.*s\\IPC$",
-				  (int)share_len, share);
-			rc = SMB2_tcon(0, tcon->ses, tree, tcon, nlsc);
-		} else {
-			scnprintf(tree, MAX_TREE_SIZE, "\\%.*s", (int)share_len,
-				  share);
-			rc = SMB2_tcon(0, tcon->ses, tree, tcon, nlsc);
-			if (!rc) {
-				rc = update_super_prepath(tcon, prefix,
-							  prefix_len);
-				break;
-			}
-		}
-		if (rc == -EREMOTE)
-			break;
-	}
-
-	if (!rc) {
-		if (it)
-			rc = dfs_cache_noreq_update_tgthint(tcon->dfs_path + 1,
-							    it);
-		else
-			rc = -ENOENT;
-	}
-	dfs_cache_free_tgts(&tl);
-out:
-	kfree(tree);
-	return rc;
-}
-#else
-static inline int __smb2_reconnect(const struct nls_table *nlsc,
-				   struct cifs_tcon *tcon)
-{
-	return SMB2_tcon(0, tcon->ses, tcon->treeName, tcon, nlsc);
-}
-#endif
-
 static int
 smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon,
 	       struct TCP_Server_Info *server)
@@ -409,7 +298,7 @@ smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon,
 	if (tcon->use_persistent)
 		tcon->need_reopen_files = true;
 
-	rc = __smb2_reconnect(nls_codepage, tcon);
+	rc = cifs_tree_connect(0, tcon, nls_codepage);
 	mutex_unlock(&tcon->ses->session_mutex);
 
 	cifs_dbg(FYI, "reconnect tcon rc = %d\n", rc);
-- 
2.27.0

Re: [PATCH 1/7] cifs: merge __{cifs,smb2}_reconnect[_tcon]() into cifs_tree_connect()

[Stefan Metzmacher]

[-- Attachment #1.1: Type: text/plain, Size: 612 bytes --]

Hi Paulo,

> +		if (tcon->ipc) {
> +			scnprintf(tree, MAX_TREE_SIZE, "\\\\%s\\IPC$", share);
> +			rc = ops->tree_connect(xid, tcon->ses, tree, tcon, nlsc);
> +		} else {
> +			scnprintf(tree, MAX_TREE_SIZE, "\\%s", share);
> +			rc = ops->tree_connect(xid, tcon->ses, tree, tcon, nlsc);
> +			if (!rc) {
> +				rc = update_super_prepath(tcon, prefix, prefix_len);
> +				break;
> +			}
> +		}

The original code used:

-		scnprintf(tree, MAX_TREE_SIZE, "\\%.*s", (int)share_len,
-			  share);

So it's no longer identical.

Was the share_len code added after my initial patch?

metze


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

Re: [PATCH 1/7] cifs: merge __{cifs,smb2}_reconnect[_tcon]() into cifs_tree_connect()

[Paulo Alcantara]

Hi,

Stefan Metzmacher <metze@samba.org> writes:

>> +		if (tcon->ipc) {
>> +			scnprintf(tree, MAX_TREE_SIZE, "\\\\%s\\IPC$", share);
>> +			rc = ops->tree_connect(xid, tcon->ses, tree, tcon, nlsc);
>> +		} else {
>> +			scnprintf(tree, MAX_TREE_SIZE, "\\%s", share);
>> +			rc = ops->tree_connect(xid, tcon->ses, tree, tcon, nlsc);
>> +			if (!rc) {
>> +				rc = update_super_prepath(tcon, prefix, prefix_len);
>> +				break;
>> +			}
>> +		}
>
> The original code used:
>
> -		scnprintf(tree, MAX_TREE_SIZE, "\\%.*s", (int)share_len,
> -			  share);
>
> So it's no longer identical.
>
> Was the share_len code added after my initial patch?

Yep.  See

      e4af35fa55b0 (cifs: handle hostnames that resolve to same ip in failover)
      bacd704a95ad (cifs: handle prefix paths in reconnect)

Re: [PATCH 1/7] cifs: merge __{cifs,smb2}_reconnect[_tcon]() into cifs_tree_connect()

[Paulo Alcantara]

Paulo Alcantara <pc@cjr.nz> writes:

> Stefan Metzmacher <metze@samba.org> writes:
>
>>> +		if (tcon->ipc) {
>>> +			scnprintf(tree, MAX_TREE_SIZE, "\\\\%s\\IPC$", share);
>>> +			rc = ops->tree_connect(xid, tcon->ses, tree, tcon, nlsc);
>>> +		} else {
>>> +			scnprintf(tree, MAX_TREE_SIZE, "\\%s", share);
>>> +			rc = ops->tree_connect(xid, tcon->ses, tree, tcon, nlsc);
>>> +			if (!rc) {
>>> +				rc = update_super_prepath(tcon, prefix, prefix_len);
>>> +				break;
>>> +			}
>>> +		}
>>
>> The original code used:
>>
>> -		scnprintf(tree, MAX_TREE_SIZE, "\\%.*s", (int)share_len,
>> -			  share);
>>
>> So it's no longer identical.
>>
>> Was the share_len code added after my initial patch?
>
> Yep.  See
>
>       e4af35fa55b0 (cifs: handle hostnames that resolve to same ip in failover)
>       bacd704a95ad (cifs: handle prefix paths in reconnect)

Oh, that's really wrong, sorry.  I should have kept the usage of
"share_len" in scnprintf() for this commit.  So, in patch 6/7, it should
use directly "share" instead.

Thanks for pointing that out.  I'll send v2 with that fix.

[PATCH 2/7] cifs: reduce number of referral requests in DFS link lookups

[Paulo Alcantara]

When looking up the DFS cache with a referral path that has more than
two path components, and is a complete prefix of an existing cache
entry, do not request another referral and just return the matched
entry as specified in MS-DFSC 3.2.5.5 Receiving a Root Referral
Request or Link Referral Request.

Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
---
 fs/cifs/dfs_cache.c | 79 ++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 68 insertions(+), 11 deletions(-)

diff --git a/fs/cifs/dfs_cache.c b/fs/cifs/dfs_cache.c
index df81c718d2fa..dae2f41e4f21 100644
--- a/fs/cifs/dfs_cache.c
+++ b/fs/cifs/dfs_cache.c
@@ -490,16 +490,7 @@ static int add_cache_entry(const char *path, unsigned int hash,
 	return 0;
 }
 
-/*
- * 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)
+static struct cache_entry *__lookup_cache_entry(const char *path)
 {
 	struct cache_entry *ce;
 	unsigned int h;
@@ -517,9 +508,75 @@ static struct cache_entry *lookup_cache_entry(const char *path,
 
 	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;
 }
 
-- 
2.27.0

[PATCH 3/7] cifs: rename reconn_inval_dfs_target()

[Paulo Alcantara]

This function has nothing to do with *invalidation* but setting up the
next target server from a cached referral.

Rename it to reconn_set_next_dfs_target().  While at it, get rid of
some meaningless checks.

Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
---
 fs/cifs/connect.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 5c3c65265478..b90ee86c0523 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -393,15 +393,14 @@ static inline int reconn_set_ipaddr(struct TCP_Server_Info *server)
 
 #ifdef CONFIG_CIFS_DFS_UPCALL
 /* These functions must be called with server->srv_mutex held */
-static void reconn_inval_dfs_target(struct TCP_Server_Info *server,
-				    struct cifs_sb_info *cifs_sb,
-				    struct dfs_cache_tgt_list *tgt_list,
-				    struct dfs_cache_tgt_iterator **tgt_it)
+static void reconn_set_next_dfs_target(struct TCP_Server_Info *server,
+				       struct cifs_sb_info *cifs_sb,
+				       struct dfs_cache_tgt_list *tgt_list,
+				       struct dfs_cache_tgt_iterator **tgt_it)
 {
 	const char *name;
 
-	if (!cifs_sb || !cifs_sb->origin_fullpath || !tgt_list ||
-	    !server->nr_targets)
+	if (!cifs_sb || !cifs_sb->origin_fullpath)
 		return;
 
 	if (!*tgt_it) {
@@ -578,7 +577,7 @@ cifs_reconnect(struct TCP_Server_Info *server)
 		 * feature is disabled, then we will retry last server we
 		 * connected to before.
 		 */
-		reconn_inval_dfs_target(server, cifs_sb, &tgt_list, &tgt_it);
+		reconn_set_next_dfs_target(server, cifs_sb, &tgt_list, &tgt_it);
 #endif
 		rc = reconn_set_ipaddr(server);
 		if (rc) {
-- 
2.27.0

[PATCH 4/7] cifs: handle empty list of targets in cifs_reconnect()

[Paulo Alcantara]

In case there were no cached DFS referrals in
reconn_setup_dfs_targets(), set cifs_sb to NULL prior to calling
reconn_set_next_dfs_target() so it would not try to access an empty
tgt_list.

Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
---
 fs/cifs/connect.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index b90ee86c0523..721ef2a53f65 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -470,11 +470,13 @@ cifs_reconnect(struct TCP_Server_Info *server)
 		sb = NULL;
 	} else {
 		cifs_sb = CIFS_SB(sb);
-
 		rc = reconn_setup_dfs_targets(cifs_sb, &tgt_list);
-		if (rc && (rc != -EOPNOTSUPP)) {
-			cifs_server_dbg(VFS, "%s: no target servers for DFS failover\n",
-				 __func__);
+		if (rc) {
+			cifs_sb = NULL;
+			if (rc != -EOPNOTSUPP) {
+				cifs_server_dbg(VFS, "%s: no target servers for DFS failover\n",
+						__func__);
+			}
 		} else {
 			server->nr_targets = dfs_cache_get_nr_tgts(&tgt_list);
 		}
-- 
2.27.0

[PATCH 5/7] cifs: handle RESP_GET_DFS_REFERRAL.PathConsumed in reconnect

[Paulo Alcantara]

Use PathConsumed field when parsing prefixes of referral paths that
either match a cache entry or are a complete prefix path of an
existing entry.

Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
---
 fs/cifs/cifsproto.h |  3 +--
 fs/cifs/connect.c   | 13 +++++++----
 fs/cifs/dfs_cache.c | 57 ++++++++++++++++++++++++++++++++++-----------
 fs/cifs/dfs_cache.h |  7 +++---
 fs/cifs/misc.c      |  7 +++---
 5 files changed, 60 insertions(+), 27 deletions(-)

diff --git a/fs/cifs/cifsproto.h b/fs/cifs/cifsproto.h
index 93b018723abf..577084487b1a 100644
--- a/fs/cifs/cifsproto.h
+++ b/fs/cifs/cifsproto.h
@@ -616,8 +616,7 @@ int smb2_parse_query_directory(struct cifs_tcon *tcon, struct kvec *rsp_iov,
 
 struct super_block *cifs_get_tcp_super(struct TCP_Server_Info *server);
 void cifs_put_tcp_super(struct super_block *sb);
-int update_super_prepath(struct cifs_tcon *tcon, const char *prefix,
-			 size_t prefix_len);
+int update_super_prepath(struct cifs_tcon *tcon, char *prefix);
 
 #ifdef CONFIG_CIFS_DFS_UPCALL
 static inline int get_dfs_path(const unsigned int xid, struct cifs_ses *ses,
diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 721ef2a53f65..2abef1c8feb3 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -5548,6 +5548,7 @@ int cifs_tree_connect(const unsigned int xid, struct cifs_tcon *tcon, const stru
 	size_t tcp_host_len;
 	const char *dfs_host;
 	size_t dfs_host_len;
+	char *share = NULL, *prefix = NULL;
 
 	tree = kzalloc(MAX_TREE_SIZE, GFP_KERNEL);
 	if (!tree)
@@ -5570,11 +5571,12 @@ int cifs_tree_connect(const unsigned int xid, struct cifs_tcon *tcon, const stru
 	extract_unc_hostname(server->hostname, &tcp_host, &tcp_host_len);
 
 	for (it = dfs_cache_get_tgt_iterator(&tl); it; it = dfs_cache_get_next_tgt(&tl, it)) {
-		const char *share, *prefix;
-		size_t share_len, prefix_len;
 		bool target_match;
 
-		rc = dfs_cache_get_tgt_share(it, &share, &share_len, &prefix, &prefix_len);
+		kfree(share);
+		kfree(prefix);
+
+		rc = dfs_cache_get_tgt_share(tcon->dfs_path + 1, it, &share, &prefix);
 		if (rc) {
 			cifs_dbg(VFS, "%s: failed to parse target share %d\n",
 				 __func__, rc);
@@ -5607,7 +5609,7 @@ int cifs_tree_connect(const unsigned int xid, struct cifs_tcon *tcon, const stru
 			scnprintf(tree, MAX_TREE_SIZE, "\\%s", share);
 			rc = ops->tree_connect(xid, tcon->ses, tree, tcon, nlsc);
 			if (!rc) {
-				rc = update_super_prepath(tcon, prefix, prefix_len);
+				rc = update_super_prepath(tcon, prefix);
 				break;
 			}
 		}
@@ -5615,6 +5617,9 @@ int cifs_tree_connect(const unsigned int xid, struct cifs_tcon *tcon, const stru
 			break;
 	}
 
+	kfree(share);
+	kfree(prefix);
+
 	if (!rc) {
 		if (it)
 			rc = dfs_cache_noreq_update_tgthint(tcon->dfs_path + 1, it);
diff --git a/fs/cifs/dfs_cache.c b/fs/cifs/dfs_cache.c
index dae2f41e4f21..a44f58bbf7ab 100644
--- a/fs/cifs/dfs_cache.c
+++ b/fs/cifs/dfs_cache.c
@@ -29,6 +29,7 @@
 
 struct cache_dfs_tgt {
 	char *name;
+	int path_consumed;
 	struct list_head list;
 };
 
@@ -350,7 +351,7 @@ static inline struct timespec64 get_expire_time(int ttl)
 }
 
 /* Allocate a new DFS target */
-static struct cache_dfs_tgt *alloc_target(const char *name)
+static struct cache_dfs_tgt *alloc_target(const char *name, int path_consumed)
 {
 	struct cache_dfs_tgt *t;
 
@@ -362,6 +363,7 @@ static struct cache_dfs_tgt *alloc_target(const char *name)
 		kfree(t);
 		return ERR_PTR(-ENOMEM);
 	}
+	t->path_consumed = path_consumed;
 	INIT_LIST_HEAD(&t->list);
 	return t;
 }
@@ -384,7 +386,7 @@ static int copy_ref_data(const struct dfs_info3_param *refs, int numrefs,
 	for (i = 0; i < numrefs; i++) {
 		struct cache_dfs_tgt *t;
 
-		t = alloc_target(refs[i].node_name);
+		t = alloc_target(refs[i].node_name, refs[i].path_consumed);
 		if (IS_ERR(t)) {
 			free_tgts(ce);
 			return PTR_ERR(t);
@@ -830,6 +832,7 @@ static int get_targets(struct cache_entry *ce, struct dfs_cache_tgt_list *tl)
 			rc = -ENOMEM;
 			goto err_free_it;
 		}
+		it->it_path_consumed = t->path_consumed;
 
 		if (ce->tgthint == t)
 			list_add(&it->it_list, head);
@@ -1320,23 +1323,26 @@ void dfs_cache_del_vol(const char *fullpath)
 /**
  * dfs_cache_get_tgt_share - parse a DFS target
  *
+ * @path: DFS full path
  * @it: DFS target iterator.
  * @share: tree name.
- * @share_len: length of tree name.
  * @prefix: prefix path.
- * @prefix_len: length of prefix path.
  *
  * Return zero if target was parsed correctly, otherwise non-zero.
  */
-int dfs_cache_get_tgt_share(const struct dfs_cache_tgt_iterator *it,
-			    const char **share, size_t *share_len,
-			    const char **prefix, size_t *prefix_len)
+int dfs_cache_get_tgt_share(char *path, const struct dfs_cache_tgt_iterator *it,
+			    char **share, char **prefix)
 {
-	char *s, sep;
+	char *s, sep, *p;
+	size_t len;
+	size_t plen1, plen2;
 
-	if (!it || !share || !share_len || !prefix || !prefix_len)
+	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;
@@ -1345,13 +1351,38 @@ int dfs_cache_get_tgt_share(const struct dfs_cache_tgt_iterator *it,
 	if (!s)
 		return -EINVAL;
 
+	/* point to prefix in target node */
 	s = strchrnul(s + 1, sep);
 
-	*share = it->it_name;
-	*share_len = s - it->it_name;
-	*prefix = *s ? s + 1 : s;
-	*prefix_len = &it->it_name[strlen(it->it_name)] - *prefix;
+	/* 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;
 }
 
diff --git a/fs/cifs/dfs_cache.h b/fs/cifs/dfs_cache.h
index bf94d08cfb5a..3d7c05194536 100644
--- a/fs/cifs/dfs_cache.h
+++ b/fs/cifs/dfs_cache.h
@@ -19,6 +19,7 @@ struct dfs_cache_tgt_list {
 
 struct dfs_cache_tgt_iterator {
 	char *it_name;
+	int it_path_consumed;
 	struct list_head it_list;
 };
 
@@ -48,10 +49,8 @@ extern int dfs_cache_add_vol(char *mntdata, struct smb_vol *vol,
 extern int dfs_cache_update_vol(const char *fullpath,
 				struct TCP_Server_Info *server);
 extern void dfs_cache_del_vol(const char *fullpath);
-
-extern int dfs_cache_get_tgt_share(const struct dfs_cache_tgt_iterator *it,
-				   const char **share, size_t *share_len,
-				   const char **prefix, size_t *prefix_len);
+extern int dfs_cache_get_tgt_share(char *path, const struct dfs_cache_tgt_iterator *it,
+				   char **share, char **prefix);
 
 static inline struct dfs_cache_tgt_iterator *
 dfs_cache_get_next_tgt(struct dfs_cache_tgt_list *tl,
diff --git a/fs/cifs/misc.c b/fs/cifs/misc.c
index e44d049142d0..764234803071 100644
--- a/fs/cifs/misc.c
+++ b/fs/cifs/misc.c
@@ -1164,8 +1164,7 @@ static inline void cifs_put_tcon_super(struct super_block *sb)
 }
 #endif
 
-int update_super_prepath(struct cifs_tcon *tcon, const char *prefix,
-			 size_t prefix_len)
+int update_super_prepath(struct cifs_tcon *tcon, char *prefix)
 {
 	struct super_block *sb;
 	struct cifs_sb_info *cifs_sb;
@@ -1179,8 +1178,8 @@ int update_super_prepath(struct cifs_tcon *tcon, const char *prefix,
 
 	kfree(cifs_sb->prepath);
 
-	if (*prefix && prefix_len) {
-		cifs_sb->prepath = kstrndup(prefix, prefix_len, GFP_ATOMIC);
+	if (prefix && *prefix) {
+		cifs_sb->prepath = kstrndup(prefix, strlen(prefix), GFP_ATOMIC);
 		if (!cifs_sb->prepath) {
 			rc = -ENOMEM;
 			goto out;
-- 
2.27.0

[PATCH 6/7] cifs: only update prefix path of DFS links in cifs_tree_connect()

[Paulo Alcantara]

For DFS root mounts that contain a prefix path, do not change them
after failover.

E.g., if the user mounts

	//srvA/root/dir1

and then lost connection to srvA, it will reconnect to

	//srvB/root/dir1

In case of DFS links, which may resolve to different prefix paths
depending on their list of targets, the following must be supported:

	- mount //srvA/root/link/bar
	- connect to //srvA/share
	- set prefix path to "bar"
	- lost connection to srvA
	- reconnect to next target: //srvB/share/foo
	- set new prefix path to "foo/bar"

In cifs_tree_connect(), check the server_type field of the cached DFS
referral to determine whether or not prefix path should be updated.

Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
---
 fs/cifs/connect.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 2abef1c8feb3..af0c19495626 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -5549,6 +5549,8 @@ int cifs_tree_connect(const unsigned int xid, struct cifs_tcon *tcon, const stru
 	const char *dfs_host;
 	size_t dfs_host_len;
 	char *share = NULL, *prefix = NULL;
+	struct dfs_info3_param ref = {0};
+	bool isroot;
 
 	tree = kzalloc(MAX_TREE_SIZE, GFP_KERNEL);
 	if (!tree)
@@ -5564,9 +5566,11 @@ int cifs_tree_connect(const unsigned int xid, struct cifs_tcon *tcon, const stru
 		goto out;
 	}
 
-	rc = dfs_cache_noreq_find(tcon->dfs_path + 1, NULL, &tl);
+	rc = dfs_cache_noreq_find(tcon->dfs_path + 1, &ref, &tl);
 	if (rc)
 		goto out;
+	isroot = ref.server_type == DFS_TYPE_ROOT;
+	free_dfs_info_param(&ref);
 
 	extract_unc_hostname(server->hostname, &tcp_host, &tcp_host_len);
 
@@ -5608,7 +5612,8 @@ int cifs_tree_connect(const unsigned int xid, struct cifs_tcon *tcon, const stru
 		} else {
 			scnprintf(tree, MAX_TREE_SIZE, "\\%s", share);
 			rc = ops->tree_connect(xid, tcon->ses, tree, tcon, nlsc);
-			if (!rc) {
+			/* Only handle prefix paths of DFS link targets */
+			if (!rc && !isroot) {
 				rc = update_super_prepath(tcon, prefix);
 				break;
 			}
-- 
2.27.0

[PATCH 7/7] cifs: document and cleanup dfs mount

[Paulo Alcantara]

cifs_mount() for DFS mounts is for a long time way too complex to
follow, mostly because it lacks some documentation, does a lot of
operations like resolving DFS roots and links, checking for path
components, perform failover, crap code, etc.

Besides adding some documentation to it, do some cleanup and ensure
that the following is implemented and supported:

    * non-DFS mounts
    * DFS failover
    * DFS root mounts
        - tcon and cifs_sb must contain DFS path (NOT including prefix)
        - if prefix path, then save it in cifs_sb and it must not be
	  changed
    * DFS link mounts
      - tcon and cifs_sb must contain DFS path (including prefix)
      - if prefix path, then save it in cifs_sb and it may be changed
    * prevent recursion on broken link referrals (MAX_NESTED_LINKS)
    * check every path component of the currently resolved
      target (including prefix), and chase them accordingly
    * make sure that DFS referrals go through newly resolved root
      servers

Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
---
 fs/cifs/connect.c | 371 +++++++++++++++++++++++-----------------------
 1 file changed, 182 insertions(+), 189 deletions(-)

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index af0c19495626..1e1f84316faa 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -4423,11 +4423,11 @@ build_unc_path_to_root(const struct smb_vol *vol,
 static int
 expand_dfs_referral(const unsigned int xid, struct cifs_ses *ses,
 		    struct smb_vol *volume_info, struct cifs_sb_info *cifs_sb,
-		    int check_prefix)
+		    char *ref_path)
 {
 	int rc;
 	struct dfs_info3_param referral = {0};
-	char *full_path = NULL, *ref_path = NULL, *mdata = NULL;
+	char *full_path = NULL, *mdata = NULL;
 
 	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NO_DFS)
 		return -EREMOTE;
@@ -4436,9 +4436,6 @@ expand_dfs_referral(const unsigned int xid, struct cifs_ses *ses,
 	if (IS_ERR(full_path))
 		return PTR_ERR(full_path);
 
-	/* For DFS paths, skip the first '\' of the UNC */
-	ref_path = check_prefix ? full_path + 1 : volume_info->UNC + 1;
-
 	rc = dfs_cache_find(xid, ses, cifs_sb->local_nls, cifs_remap(cifs_sb),
 			    ref_path, &referral, NULL);
 	if (!rc) {
@@ -4501,13 +4498,10 @@ static int update_vol_info(const struct dfs_cache_tgt_iterator *tgt_it,
 	return 0;
 }
 
-static int setup_dfs_tgt_conn(const char *path,
+static int setup_dfs_tgt_conn(const char *path, const char *full_path,
 			      const struct dfs_cache_tgt_iterator *tgt_it,
-			      struct cifs_sb_info *cifs_sb,
-			      struct smb_vol *vol,
-			      unsigned int *xid,
-			      struct TCP_Server_Info **server,
-			      struct cifs_ses **ses,
+			      struct cifs_sb_info *cifs_sb, struct smb_vol *vol, unsigned int *xid,
+			      struct TCP_Server_Info **server, struct cifs_ses **ses,
 			      struct cifs_tcon **tcon)
 {
 	int rc;
@@ -4521,8 +4515,7 @@ static int setup_dfs_tgt_conn(const char *path,
 	if (rc)
 		return rc;
 
-	mdata = cifs_compose_mount_options(cifs_sb->mountdata, path, &ref,
-					   &fake_devname);
+	mdata = cifs_compose_mount_options(cifs_sb->mountdata, full_path + 1, &ref, &fake_devname);
 	free_dfs_info_param(&ref);
 
 	if (IS_ERR(mdata)) {
@@ -4545,7 +4538,7 @@ static int setup_dfs_tgt_conn(const char *path,
 		mount_put_conns(cifs_sb, *xid, *server, *ses, *tcon);
 		rc = mount_get_conns(&fake_vol, cifs_sb, xid, server, ses,
 				     tcon);
-		if (!rc) {
+		if (!rc || (*server && *ses)) {
 			/*
 			 * We were able to connect to new target server.
 			 * Update current volume info with new target server.
@@ -4557,14 +4550,10 @@ static int setup_dfs_tgt_conn(const char *path,
 	return rc;
 }
 
-static int mount_do_dfs_failover(const char *path,
-				 struct cifs_sb_info *cifs_sb,
-				 struct smb_vol *vol,
-				 struct cifs_ses *root_ses,
-				 unsigned int *xid,
-				 struct TCP_Server_Info **server,
-				 struct cifs_ses **ses,
-				 struct cifs_tcon **tcon)
+static int do_dfs_failover(const char *path, const char *full_path, struct cifs_sb_info *cifs_sb,
+			   struct smb_vol *vol, struct cifs_ses *root_ses, unsigned int *xid,
+			   struct TCP_Server_Info **server, struct cifs_ses **ses,
+			   struct cifs_tcon **tcon)
 {
 	int rc;
 	struct dfs_cache_tgt_list tgt_list;
@@ -4583,9 +4572,9 @@ static int mount_do_dfs_failover(const char *path,
 		if (rc)
 			break;
 		/* Connect to next DFS target */
-		rc = setup_dfs_tgt_conn(path, tgt_it, cifs_sb, vol, xid, server,
-					ses, tcon);
-		if (!rc || rc == -EACCES || rc == -EOPNOTSUPP)
+		rc = setup_dfs_tgt_conn(path, full_path, tgt_it, cifs_sb, vol, xid, server, ses,
+					tcon);
+		if (!rc || (*server && *ses))
 			break;
 	}
 	if (!rc) {
@@ -4755,207 +4744,209 @@ static int is_path_remote(struct cifs_sb_info *cifs_sb, struct smb_vol *vol,
 }
 
 #ifdef CONFIG_CIFS_DFS_UPCALL
-static inline void set_root_tcon(struct cifs_sb_info *cifs_sb,
-				 struct cifs_tcon *tcon,
-				 struct cifs_tcon **root)
+static void set_root_ses(struct cifs_sb_info *cifs_sb, struct cifs_ses *ses,
+			 struct cifs_ses **root_ses)
 {
-	spin_lock(&cifs_tcp_ses_lock);
-	tcon->tc_count++;
-	tcon->remap = cifs_remap(cifs_sb);
-	spin_unlock(&cifs_tcp_ses_lock);
-	*root = tcon;
+	if (ses) {
+		spin_lock(&cifs_tcp_ses_lock);
+		ses->ses_count++;
+		ses->tcon_ipc->remap = cifs_remap(cifs_sb);
+		spin_unlock(&cifs_tcp_ses_lock);
+	}
+	*root_ses = ses;
+}
+
+static void put_root_ses(struct cifs_ses *ses)
+{
+	if (ses)
+		cifs_put_smb_ses(ses);
+}
+
+/* Check if a path component is remote and then update @dfs_path accordingly */
+static int check_dfs_prepath(struct cifs_sb_info *cifs_sb, struct smb_vol *vol,
+			     const unsigned int xid, struct TCP_Server_Info *server,
+			     struct cifs_tcon *tcon, char **dfs_path)
+{
+	char *path, *s;
+	char sep = CIFS_DIR_SEP(cifs_sb), tmp;
+	char *npath;
+	int rc = 0;
+	int added_treename = tcon->Flags & SMB_SHARE_IS_IN_DFS;
+	int skip = added_treename;
+
+	path = cifs_build_path_to_root(vol, cifs_sb, tcon, added_treename);
+	if (!path)
+		return -ENOMEM;
+
+	/*
+	 * Walk through the path components in @path and check if they're accessible. In case any of
+	 * the components is -EREMOTE, then update @dfs_path with the next DFS referral request path
+	 * (NOT including the remaining components).
+	 */
+	s = path;
+	do {
+		/* skip separators */
+		while (*s && *s == sep)
+			s++;
+		if (!*s)
+			break;
+		/* next separator */
+		while (*s && *s != sep)
+			s++;
+		/*
+		 * if the treename is added, we then have to skip the first
+		 * part within the separators
+		 */
+		if (skip) {
+			skip = 0;
+			continue;
+		}
+		tmp = *s;
+		*s = 0;
+		rc = server->ops->is_path_accessible(xid, tcon, cifs_sb, path);
+		if (rc && rc == -EREMOTE) {
+			struct smb_vol v = {NULL};
+			/* if @path contains a tree name, skip it in the prefix path */
+			if (added_treename) {
+				rc = cifs_parse_devname(path, &v);
+				if (rc)
+					break;
+				rc = -EREMOTE;
+				npath = build_unc_path_to_root(&v, cifs_sb, true);
+				cifs_cleanup_volume_info_contents(&v);
+			} else {
+				v.UNC = vol->UNC;
+				v.prepath = path + 1;
+				npath = build_unc_path_to_root(&v, cifs_sb, true);
+			}
+			if (IS_ERR(npath)) {
+				rc = PTR_ERR(npath);
+				break;
+			}
+			kfree(*dfs_path);
+			*dfs_path = npath;
+		}
+		*s = tmp;
+	} while (rc == 0);
+
+	kfree(path);
+	return rc;
 }
 
 int cifs_mount(struct cifs_sb_info *cifs_sb, struct smb_vol *vol)
 {
 	int rc = 0;
 	unsigned int xid;
-	struct cifs_ses *ses;
-	struct cifs_tcon *root_tcon = NULL;
+	struct TCP_Server_Info *server = NULL;
+	struct cifs_ses *ses = NULL, *root_ses = NULL;
 	struct cifs_tcon *tcon = NULL;
-	struct TCP_Server_Info *server;
-	char *root_path = NULL, *full_path = NULL;
-	char *old_mountdata, *origin_mountdata = NULL;
-	int count;
+	int count = 0;
+	char *ref_path = NULL, *full_path = NULL;
+	char *oldmnt = NULL;
+	char *mntdata = NULL;
 
 	rc = mount_get_conns(vol, cifs_sb, &xid, &server, &ses, &tcon);
-	if (!rc && tcon) {
-		/* If not a standalone DFS root, then check if path is remote */
-		rc = dfs_cache_find(xid, ses, cifs_sb->local_nls,
-				    cifs_remap(cifs_sb), vol->UNC + 1, NULL,
-				    NULL);
-		if (rc) {
-			rc = is_path_remote(cifs_sb, vol, xid, server, tcon);
-			if (!rc)
-				goto out;
-			if (rc != -EREMOTE)
-				goto error;
-		}
-	}
 	/*
-	 * If first DFS target server went offline and we failed to connect it,
-	 * server and ses pointers are NULL at this point, though we still have
-	 * chance to get a cached DFS referral in expand_dfs_referral() and
-	 * retry next target available in it.
+	 * Unconditionally try to get an DFS referral (even cached) to determine whether it is an
+	 * DFS mount.
 	 *
-	 * If a NULL ses ptr is passed to dfs_cache_find(), a lookup will be
-	 * performed against DFS path and *no* requests will be sent to server
-	 * for any new DFS referrals. Hence it's safe to skip checking whether
-	 * server or ses ptr is NULL.
+	 * Skip prefix path to provide support for DFS referrals from w2k8 servers which don't seem
+	 * to respond with PATH_NOT_COVERED to requests that include the prefix.
 	 */
-	if (rc == -EACCES || rc == -EOPNOTSUPP)
-		goto error;
-
-	root_path = build_unc_path_to_root(vol, cifs_sb, false);
-	if (IS_ERR(root_path)) {
-		rc = PTR_ERR(root_path);
-		root_path = NULL;
-		goto error;
-	}
-
-	full_path = build_unc_path_to_root(vol, cifs_sb, true);
-	if (IS_ERR(full_path)) {
-		rc = PTR_ERR(full_path);
-		full_path = NULL;
-		goto error;
-	}
-	/*
-	 * Perform an unconditional check for whether there are DFS
-	 * referrals for this path without prefix, to provide support
-	 * for DFS referrals from w2k8 servers which don't seem to respond
-	 * with PATH_NOT_COVERED to requests that include the prefix.
-	 * Chase the referral if found, otherwise continue normally.
-	 */
-	old_mountdata = cifs_sb->mountdata;
-	(void)expand_dfs_referral(xid, ses, vol, cifs_sb, false);
-
-	if (cifs_sb->mountdata == NULL) {
-		rc = -ENOENT;
-		goto error;
-	}
-
-	/* Save DFS root volume information for DFS refresh worker */
-	origin_mountdata = kstrndup(cifs_sb->mountdata,
-				    strlen(cifs_sb->mountdata), GFP_KERNEL);
-	if (!origin_mountdata) {
-		rc = -ENOMEM;
-		goto error;
-	}
-
-	if (cifs_sb->mountdata != old_mountdata) {
-		/* If we were redirected, reconnect to new target server */
-		mount_put_conns(cifs_sb, xid, server, ses, tcon);
-		rc = mount_get_conns(vol, cifs_sb, &xid, &server, &ses, &tcon);
-	}
-	if (rc) {
-		if (rc == -EACCES || rc == -EOPNOTSUPP)
-			goto error;
-		/* Perform DFS failover to any other DFS targets */
-		rc = mount_do_dfs_failover(root_path + 1, cifs_sb, vol, NULL,
-					   &xid, &server, &ses, &tcon);
+	if (dfs_cache_find(xid, ses, cifs_sb->local_nls, cifs_remap(cifs_sb), vol->UNC + 1, NULL,
+			   NULL)) {
+		/* No DFS referral was returned.  Looks like a regular share. */
 		if (rc)
 			goto error;
+		/* Check if it is fully accessible and then mount it */
+		rc = is_path_remote(cifs_sb, vol, xid, server, tcon);
+		if (!rc)
+			goto out;
+		if (rc != -EREMOTE)
+			goto error;
 	}
-
-	kfree(root_path);
-	root_path = build_unc_path_to_root(vol, cifs_sb, false);
-	if (IS_ERR(root_path)) {
-		rc = PTR_ERR(root_path);
-		root_path = NULL;
+	/* Save mount options */
+	mntdata = kstrndup(cifs_sb->mountdata, strlen(cifs_sb->mountdata), GFP_KERNEL);
+	if (!mntdata) {
+		rc = -ENOMEM;
+		goto error;
+	}
+	/* Get path of DFS root */
+	ref_path = build_unc_path_to_root(vol, cifs_sb, false);
+	if (IS_ERR(ref_path)) {
+		rc = PTR_ERR(ref_path);
+		ref_path = NULL;
 		goto error;
 	}
-	/* Cache out resolved root server */
-	(void)dfs_cache_find(xid, ses, cifs_sb->local_nls, cifs_remap(cifs_sb),
-			     root_path + 1, NULL, NULL);
-	kfree(root_path);
-	root_path = NULL;
-
-	set_root_tcon(cifs_sb, tcon, &root_tcon);
-
-	for (count = 1; ;) {
-		if (!rc && tcon) {
-			rc = is_path_remote(cifs_sb, vol, xid, server, tcon);
-			if (!rc || rc != -EREMOTE)
-				break;
-		}
-		/*
-		 * BB: when we implement proper loop detection,
-		 *     we will remove this check. But now we need it
-		 *     to prevent an indefinite loop if 'DFS tree' is
-		 *     misconfigured (i.e. has loops).
-		 */
-		if (count++ > MAX_NESTED_LINKS) {
-			rc = -ELOOP;
-			break;
-		}
 
+	set_root_ses(cifs_sb, ses, &root_ses);
+	do {
+		/* Save full path of last DFS path we used to resolve final target server */
 		kfree(full_path);
-		full_path = build_unc_path_to_root(vol, cifs_sb, true);
+		full_path = build_unc_path_to_root(vol, cifs_sb, !!count);
 		if (IS_ERR(full_path)) {
 			rc = PTR_ERR(full_path);
-			full_path = NULL;
 			break;
 		}
-
-		old_mountdata = cifs_sb->mountdata;
-		rc = expand_dfs_referral(xid, root_tcon->ses, vol, cifs_sb,
-					 true);
+		/* Chase referral */
+		oldmnt = cifs_sb->mountdata;
+		rc = expand_dfs_referral(xid, root_ses, vol, cifs_sb, ref_path + 1);
 		if (rc)
 			break;
-
-		if (cifs_sb->mountdata != old_mountdata) {
+		/* Connect to new DFS target only if we were redirected */
+		if (oldmnt != cifs_sb->mountdata) {
 			mount_put_conns(cifs_sb, xid, server, ses, tcon);
-			rc = mount_get_conns(vol, cifs_sb, &xid, &server, &ses,
-					     &tcon);
-			/*
-			 * Ensure that DFS referrals go through new root server.
-			 */
-			if (!rc && tcon &&
-			    (tcon->share_flags & (SHI1005_FLAGS_DFS |
-						  SHI1005_FLAGS_DFS_ROOT))) {
-				cifs_put_tcon(root_tcon);
-				set_root_tcon(cifs_sb, tcon, &root_tcon);
-			}
+			rc = mount_get_conns(vol, cifs_sb, &xid, &server, &ses, &tcon);
 		}
-		if (rc) {
-			if (rc == -EACCES || rc == -EOPNOTSUPP)
-				break;
-			/* Perform DFS failover to any other DFS targets */
-			rc = mount_do_dfs_failover(full_path + 1, cifs_sb, vol,
-						   root_tcon->ses, &xid,
-						   &server, &ses, &tcon);
-			if (rc == -EACCES || rc == -EOPNOTSUPP || !server ||
-			    !ses)
-				goto error;
+		if (rc && !server && !ses) {
+			/* Failed to connect. Try to connect to other targets in the referral. */
+			rc = do_dfs_failover(ref_path + 1, full_path, cifs_sb, vol, root_ses, &xid,
+					     &server, &ses, &tcon);
 		}
-	}
-	cifs_put_tcon(root_tcon);
+		if (rc == -EACCES || rc == -EOPNOTSUPP || !server || !ses)
+			break;
+		if (!tcon)
+			continue;
+		/* Make sure that requests go through new root servers */
+		if (tcon->share_flags & (SHI1005_FLAGS_DFS | SHI1005_FLAGS_DFS_ROOT)) {
+			put_root_ses(root_ses);
+			set_root_ses(cifs_sb, ses, &root_ses);
+		}
+		/* Check for remaining path components and then continue chasing them (-EREMOTE) */
+		rc = check_dfs_prepath(cifs_sb, vol, xid, server, tcon, &ref_path);
+		/* Prevent recursion on broken link referrals */
+		if (rc == -EREMOTE && ++count > MAX_NESTED_LINKS)
+			rc = -ELOOP;
+	} while (rc == -EREMOTE);
 
 	if (rc)
 		goto error;
-
-	spin_lock(&cifs_tcp_ses_lock);
-	if (!tcon->dfs_path) {
-		/* Save full path in new tcon to do failover when reconnecting tcons */
-		tcon->dfs_path = full_path;
-		full_path = NULL;
-		tcon->remap = cifs_remap(cifs_sb);
-	}
-	cifs_sb->origin_fullpath = kstrndup(tcon->dfs_path,
-					    strlen(tcon->dfs_path),
-					    GFP_ATOMIC);
+	put_root_ses(root_ses);
+	root_ses = NULL;
+	kfree(ref_path);
+	ref_path = NULL;
+	/* Store DFS full path in both superblock and tree connect structures.
+	 *
+	 * For DFS root mounts, the prefix path (cifs_sb->prepath) is preversed during reconnect so
+	 * only the root path is set in cifs_sb->origin_fullpath and tcon->dfs_path. And for DFS
+	 * links, the prefix path is included in both and may be changed during reconnect.  See
+	 * cifs_tree_connect().
+	 */
+	cifs_sb->origin_fullpath = kstrndup(full_path, strlen(full_path), GFP_KERNEL);
 	if (!cifs_sb->origin_fullpath) {
-		spin_unlock(&cifs_tcp_ses_lock);
 		rc = -ENOMEM;
 		goto error;
 	}
+	spin_lock(&cifs_tcp_ses_lock);
+	tcon->dfs_path = full_path;
+	full_path = NULL;
+	tcon->remap = cifs_remap(cifs_sb);
 	spin_unlock(&cifs_tcp_ses_lock);
 
-	rc = dfs_cache_add_vol(origin_mountdata, vol, cifs_sb->origin_fullpath);
-	if (rc) {
-		kfree(cifs_sb->origin_fullpath);
+	/* Add original volume information for DFS cache to be used when refreshing referrals */
+	rc = dfs_cache_add_vol(mntdata, vol, cifs_sb->origin_fullpath);
+	if (rc)
 		goto error;
-	}
 	/*
 	 * After reconnecting to a different server, unique ids won't
 	 * match anymore, so we disable serverino. This prevents
@@ -4977,9 +4968,11 @@ int cifs_mount(struct cifs_sb_info *cifs_sb, struct smb_vol *vol)
 	return mount_setup_tlink(cifs_sb, ses, tcon);
 
 error:
+	kfree(ref_path);
 	kfree(full_path);
-	kfree(root_path);
-	kfree(origin_mountdata);
+	kfree(mntdata);
+	kfree(cifs_sb->origin_fullpath);
+	put_root_ses(root_ses);
 	mount_put_conns(cifs_sb, xid, server, ses, tcon);
 	return rc;
 }
-- 
2.27.0