cifs: Add support for failover in smb2_reconnect()

After a successful failover in cifs_reconnect(), the smb2_reconnect()
function will make sure to reconnect every tcon to new target server.

For SMB2+.
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/cifsproto.h

@@ -565,6 +565,8 @@ void cifs_free_hash(struct crypto_shash **shash, struct sdesc **sdesc);
 extern void rqst_page_get_length(struct smb_rqst *rqst, unsigned int page,
 				unsigned int *len, unsigned int *offset);
 
+void extract_unc_hostname(const char *unc, const char **h, size_t *len);
+
 #ifdef CONFIG_CIFS_DFS_UPCALL
 static inline int get_dfs_path(const unsigned int xid, struct cifs_ses *ses,
 			       const char *old_path,

fs/cifs/misc.c

@@ -952,3 +952,20 @@ void rqst_page_get_length(struct smb_rqst *rqst, unsigned int page,
 	else if (page == 0)
 		*len = rqst->rq_pagesz - rqst->rq_offset;
 }
+
+void extract_unc_hostname(const char *unc, const char **h, size_t *len)
+{
+	const char *end;
+
+	/* skip initial slashes */
+	while (*unc && (*unc == '\\' || *unc == '/'))
+		unc++;
+
+	end = unc;
+
+	while (*end && !(*end == '\\' || *end == '/'))
+		end++;
+
+	*h = unc;
+	*len = end - unc;
+}

fs/cifs/smb2pdu.c

@@ -50,6 +50,9 @@
 #include "cifs_spnego.h"
 #include "smbdirect.h"
 #include "trace.h"
+#ifdef CONFIG_CIFS_DFS_UPCALL
+#include "dfs_cache.h"
+#endif
 
 /*
  *  The following table defines the expected "StructureSize" of SMB2 requests
@@ -152,6 +155,77 @@ 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 dfs_cache_tgt_list tl;
+	struct dfs_cache_tgt_iterator *it = NULL;
+	char tree[MAX_TREE_SIZE + 1];
+	const char *tcp_host;
+	size_t tcp_host_len;
+	const char *dfs_host;
+	size_t dfs_host_len;
+
+	if (tcon->ipc) {
+		snprintf(tree, sizeof(tree), "\\\\%s\\IPC$",
+			 tcon->ses->server->hostname);
+		return SMB2_tcon(0, tcon->ses, tree, tcon, nlsc);
+	}
+
+	if (!tcon->dfs_path)
+		return SMB2_tcon(0, tcon->ses, tcon->treeName, tcon, nlsc);
+
+	rc = dfs_cache_noreq_find(tcon->dfs_path + 1, NULL, &tl);
+	if (rc)
+		return rc;
+
+	extract_unc_hostname(tcon->ses->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 *tgt = dfs_cache_get_tgt_name(it);
+
+		extract_unc_hostname(tgt, &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: skipping %.*s, doesn't match %.*s",
+				 __func__,
+				 (int)dfs_host_len, dfs_host,
+				 (int)tcp_host_len, tcp_host);
+			continue;
+		}
+
+		snprintf(tree, sizeof(tree), "\\%s", tgt);
+
+		rc = SMB2_tcon(0, tcon->ses, tree, tcon, nlsc);
+		if (!rc)
+			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);
+	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)
 {
@@ -159,6 +233,7 @@ smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon)
 	struct nls_table *nls_codepage;
 	struct cifs_ses *ses;
 	struct TCP_Server_Info *server;
+	int retries;
 
 	/*
 	 * SMB2s NegProt, SessSetup, Logoff do not have tcon yet so
@@ -192,9 +267,12 @@ smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon)
 	ses = tcon->ses;
 	server = ses->server;
 
+	retries = server->nr_targets;
+
 	/*
-	 * Give demultiplex thread up to 10 seconds to reconnect, should be
-	 * greater than cifs socket timeout which is 7 seconds
+	 * Give demultiplex thread up to 10 seconds to each target available for
+	 * reconnect -- should be greater than cifs socket timeout which is 7
+	 * seconds.
 	 */
 	while (server->tcpStatus == CifsNeedReconnect) {
 		/*
@@ -225,6 +303,9 @@ smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon)
 		if (server->tcpStatus != CifsNeedReconnect)
 			break;
 
+		if (--retries)
+			continue;
+
 		/*
 		 * on "soft" mounts we wait once. Hard mounts keep
 		 * retrying until process is killed or server comes
@@ -234,6 +315,7 @@ smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon)
 			cifs_dbg(FYI, "gave up waiting on reconnect in smb_init\n");
 			return -EHOSTDOWN;
 		}
+		retries = server->nr_targets;
 	}
 
 	if (!tcon->ses->need_reconnect && !tcon->need_reconnect)
@@ -271,7 +353,7 @@ smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon)
 	if (tcon->use_persistent)
 		tcon->need_reopen_files = true;
 
-	rc = SMB2_tcon(0, tcon->ses, tcon->treeName, tcon, nls_codepage);
+	rc = __smb2_reconnect(nls_codepage, tcon);
 	mutex_unlock(&tcon->ses->session_mutex);
 
 	cifs_dbg(FYI, "reconnect tcon rc = %d\n", rc);