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) {
@@ -2469,13 +2513,66 @@ 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
@@ -2484,16 +2581,7 @@ mount_fail_check:
 	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;
 }