Remote DFS root support.

Allows to mount share on a server that returns -EREMOTE
 at the tree connect stage or at the check on a full path
 accessibility.
Signed-off-by: Igor Mammedov <niallain@gmail.com>
Acked-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

fs/cifs/connect.c

@@ -2214,9 +2214,56 @@ is_path_accessible(int xid, struct cifsTconInfo *tcon,
 	return rc;
 }
 
+static void
+cleanup_volume_info(struct smb_vol **pvolume_info)
+{
+	struct smb_vol *volume_info;
+
+	if (!pvolume_info && !*pvolume_info)
+		return;
+
+	volume_info = *pvolume_info;
+	kzfree(volume_info->password);
+	kfree(volume_info->UNC);
+	kfree(volume_info->prepath);
+	kfree(volume_info);
+	*pvolume_info = NULL;
+	return;
+}
+
+/* build_path_to_root returns full path to root when
+ * we do not have an exiting connection (tcon) */
+static char *
+build_unc_path_to_root(const struct smb_vol *volume_info,
+		const struct cifs_sb_info *cifs_sb)
+{
+	char *full_path;
+
+	int unc_len = strnlen(volume_info->UNC, MAX_TREE_SIZE + 1);
+	full_path = kmalloc(unc_len + cifs_sb->prepathlen + 1, GFP_KERNEL);
+	if (full_path == NULL)
+		return ERR_PTR(-ENOMEM);
+
+	strncpy(full_path, volume_info->UNC, unc_len);
+	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_POSIX_PATHS) {
+		int i;
+		for (i = 0; i < unc_len; i++) {
+			if (full_path[i] == '\\')
+				full_path[i] = '/';
+		}
+	}
+
+	if (cifs_sb->prepathlen)
+		strncpy(full_path + unc_len, cifs_sb->prepath,
+				cifs_sb->prepathlen);
+
+	full_path[unc_len + cifs_sb->prepathlen] = 0; /* add trailing null */
+	return full_path;
+}
+
 int
 cifs_mount(struct super_block *sb, struct cifs_sb_info *cifs_sb,
-	   char *mount_data, const char *devname)
+		char *mount_data_global, const char *devname)
 {
 	int rc = 0;
 	int xid;
@@ -2225,6 +2272,13 @@ cifs_mount(struct super_block *sb, struct cifs_sb_info *cifs_sb,
 	struct cifsTconInfo *tcon = NULL;
 	struct TCP_Server_Info *srvTcp = NULL;
 	char   *full_path;
+	struct dfs_info3_param *referrals = NULL;
+	unsigned int num_referrals = 0;
+
+	char *mount_data = mount_data_global;
+
+try_mount_again:
+	full_path = NULL;
 
 	xid = GetXid();
 
@@ -2371,11 +2425,9 @@ cifs_mount(struct super_block *sb, struct cifs_sb_info *cifs_sb,
 				}
 			}
 
-			/* check for null share name ie connect to dfs root */
 			if ((strchr(volume_info->UNC + 3, '\\') == NULL)
 			    && (strchr(volume_info->UNC + 3, '/') == NULL)) {
-				/* rc = connect_to_dfs_path(...) */
-				cFYI(1, ("DFS root not supported"));
+				cERROR(1, ("Missing share name"));
 				rc = -ENODEV;
 				goto mount_fail_check;
 			} else {
@@ -2392,7 +2444,7 @@ cifs_mount(struct super_block *sb, struct cifs_sb_info *cifs_sb,
 				}
 			}
 			if (rc)
-				goto mount_fail_check;
+				goto remote_path_check;
 			tcon->seal = volume_info->seal;
 			write_lock(&cifs_tcp_ses_lock);
 			list_add(&tcon->tcon_list, &pSesInfo->tcon_list);
@@ -2417,19 +2469,9 @@ cifs_mount(struct super_block *sb, struct cifs_sb_info *cifs_sb,
 	/* BB FIXME fix time_gran to be larger for LANMAN sessions */
 	sb->s_time_gran = 100;
 
-mount_fail_check:
-	/* on error free sesinfo and tcon struct if needed */
-	if (rc) {
-		/* If find_unc succeeded then rc == 0 so we can not end */
-		/* up accidently freeing someone elses tcon struct */
-		if (tcon)
-			cifs_put_tcon(tcon);
-		else if (pSesInfo)
-			cifs_put_smb_ses(pSesInfo);
-		else
-			cifs_put_tcp_session(srvTcp);
-		goto out;
-	}
+	if (rc)
+		goto remote_path_check;
+
 	cifs_sb->tcon = tcon;
 
 	/* do not care if following two calls succeed - informational */
@@ -2461,7 +2503,9 @@ mount_fail_check:
 		cifs_sb->rsize = min(cifs_sb->rsize,
 			       (tcon->ses->server->maxBuf - MAX_CIFS_HDR_SIZE));
 
-	if (!rc && cifs_sb->prepathlen) {
+remote_path_check:
+	/* check if a whole path (including prepath) is not remote */
+	if (!rc && cifs_sb->prepathlen && tcon) {
 		/* build_path_to_root works only when we have a valid tcon */
 		full_path = cifs_build_path_to_root(cifs_sb);
 		if (full_path == NULL) {
@@ -2469,31 +2513,75 @@ mount_fail_check:
 			goto mount_fail_check;
 		}
 		rc = is_path_accessible(xid, tcon, cifs_sb, full_path);
-		if (rc) {
-			cERROR(1, ("Path %s in not accessible: %d",
-						full_path, rc));
+		if (rc != -EREMOTE) {
 			kfree(full_path);
 			goto mount_fail_check;
 		}
 		kfree(full_path);
 	}
 
+	/* get referral if needed */
+	if (rc == -EREMOTE) {
+		/* convert forward to back slashes in prepath here if needed */
+		if ((cifs_sb->mnt_cifs_flags & CIFS_MOUNT_POSIX_PATHS) == 0)
+			convert_delimiter(cifs_sb->prepath,
+					CIFS_DIR_SEP(cifs_sb));
+		full_path = build_unc_path_to_root(volume_info, cifs_sb);
+		if (IS_ERR(full_path)) {
+			rc = PTR_ERR(full_path);
+			goto mount_fail_check;
+		}
+
+		cFYI(1, ("Getting referral for: %s", full_path));
+		rc = get_dfs_path(xid, pSesInfo , full_path + 1,
+			cifs_sb->local_nls, &num_referrals, &referrals,
+			cifs_sb->mnt_cifs_flags & CIFS_MOUNT_MAP_SPECIAL_CHR);
+		if (!rc && num_referrals > 0) {
+			char *fake_devname = NULL;
+
+			if (mount_data != mount_data_global)
+				kfree(mount_data);
+			mount_data = cifs_compose_mount_options(
+					cifs_sb->mountdata, full_path + 1,
+					referrals, &fake_devname);
+			kfree(fake_devname);
+			free_dfs_info_array(referrals, num_referrals);
+
+			if (tcon)
+				cifs_put_tcon(tcon);
+			else if (pSesInfo)
+				cifs_put_smb_ses(pSesInfo);
+
+			cleanup_volume_info(&volume_info);
+			FreeXid(xid);
+			kfree(full_path);
+			goto try_mount_again;
+		}
+	}
+
+mount_fail_check:
+	/* on error free sesinfo and tcon struct if needed */
+	if (rc) {
+		if (mount_data != mount_data_global)
+			kfree(mount_data);
+		/* If find_unc succeeded then rc == 0 so we can not end */
+		/* up accidently freeing someone elses tcon struct */
+		if (tcon)
+			cifs_put_tcon(tcon);
+		else if (pSesInfo)
+			cifs_put_smb_ses(pSesInfo);
+		else
+			cifs_put_tcp_session(srvTcp);
+		goto out;
+	}
+
 	/* volume_info->password is freed above when existing session found
 	(in which case it is not needed anymore) but when new sesion is created
 	the password ptr is put in the new session structure (in which case the
 	password will be freed at unmount time) */
 out:
 	/* zero out password before freeing */
-	if (volume_info) {
-		if (volume_info->password != NULL) {
-			memset(volume_info->password, 0,
-				strlen(volume_info->password));
-			kfree(volume_info->password);
-		}
-		kfree(volume_info->UNC);
-		kfree(volume_info->prepath);
-		kfree(volume_info);
-	}
+	cleanup_volume_info(&volume_info);
 	FreeXid(xid);
 	return rc;
 }