cifs: reduce roundtrips on create/qinfo requests

To work around some Window servers that return
STATUS_OBJECT_NAME_INVALID on query infos under DFS namespaces that
contain non-ASCII characters, we started checking for -ENOENT on every
file open, and if so, then send additional requests to figure out
whether it is a DFS link or not.  It means that all those requests
will be sent to every non-existing file.

So, in order to reduce the number of roundtrips, check earlier whether
status code is STATUS_OBJECT_NAME_INVALID and tcon supports dfs, and
if so, then map -ENOENT to -EREMOTE so mount or automount will take
care of chasing the DFS link -- if it isn't an DFS link, then -ENOENT
will be returned appropriately.

Before patch

  SMB2 438 Create Request File: ada.test\dfs\foo;GetInfo Request...
  SMB2 310 Create Response, Error: STATUS_OBJECT_NAME_NOT_FOUND;...
  SMB2 228 Ioctl Request FSCTL_DFS_GET_REFERRALS, File: \ada.test\dfs\foo
  SMB2 143 Ioctl Response, Error: STATUS_OBJECT_PATH_NOT_FOUND
  SMB2 438 Create Request File: ada.test\dfs\foo;GetInfo Request...
  SMB2 310 Create Response, Error: STATUS_OBJECT_NAME_NOT_FOUND;...
  SMB2 228 Ioctl Request FSCTL_DFS_GET_REFERRALS, File: \ada.test\dfs\foo
  SMB2 143 Ioctl Response, Error: STATUS_OBJECT_PATH_NOT_FOUND

After patch

  SMB2 438 Create Request File: ada.test\dfs\foo;GetInfo Request...
  SMB2 310 Create Response, Error: STATUS_OBJECT_NAME_NOT_FOUND;...
  SMB2 438 Create Request File: ada.test\dfs\foo;GetInfo Request...
  SMB2 310 Create Response, Error: STATUS_OBJECT_NAME_NOT_FOUND;...

Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Signed-off-by: Steve French <stfrench@microsoft.com>

1 files changed, 33 insertions, 13 deletions

diff --git a/fs/cifs/smb2inode.c b/fs/cifs/smb2inode.c
index fbd46db1023a..8521adf9ce79 100644
--- a/fs/cifs/smb2inode.c
+++ b/fs/cifs/smb2inode.c
@@ -556,22 +556,42 @@ int smb2_query_path_info(const unsigned int xid, struct cifs_tcon *tcon,
 	rc = smb2_compound_op(xid, tcon, cifs_sb, full_path, FILE_READ_ATTRIBUTES, FILE_OPEN,
 			      create_options, ACL_NO_MODE, data, SMB2_OP_QUERY_INFO, cfile,
 			      NULL, NULL, err_iov, err_buftype);
-	if (rc == -EOPNOTSUPP) {
-		if (err_iov[0].iov_base && err_buftype[0] != CIFS_NO_BUFFER &&
-		    ((struct smb2_hdr *)err_iov[0].iov_base)->Command == SMB2_CREATE &&
-		    ((struct smb2_hdr *)err_iov[0].iov_base)->Status == STATUS_STOPPED_ON_SYMLINK) {
-			rc = smb2_parse_symlink_response(cifs_sb, err_iov, &data->symlink_target);
+	if (rc) {
+		struct smb2_hdr *hdr = err_iov[0].iov_base;
+
+		if (unlikely(!hdr || err_buftype[0] == CIFS_NO_BUFFER))
+			goto out;
+		if (rc == -EOPNOTSUPP && hdr->Command == SMB2_CREATE &&
+		    hdr->Status == STATUS_STOPPED_ON_SYMLINK) {
+			rc = smb2_parse_symlink_response(cifs_sb, err_iov,
+							 &data->symlink_target);
 			if (rc)
 				goto out;
-		}
-		*reparse = true;
-		create_options |= OPEN_REPARSE_POINT;
 
-		/* Failed on a symbolic link - query a reparse point info */
-		cifs_get_readable_path(tcon, full_path, &cfile);
-		rc = smb2_compound_op(xid, tcon, cifs_sb, full_path, FILE_READ_ATTRIBUTES,
-				      FILE_OPEN, create_options, ACL_NO_MODE, data,
-				      SMB2_OP_QUERY_INFO, cfile, NULL, NULL, NULL, NULL);
+			*reparse = true;
+			create_options |= OPEN_REPARSE_POINT;
+
+			/* Failed on a symbolic link - query a reparse point info */
+			cifs_get_readable_path(tcon, full_path, &cfile);
+			rc = smb2_compound_op(xid, tcon, cifs_sb, full_path,
+					      FILE_READ_ATTRIBUTES, FILE_OPEN,
+					      create_options, ACL_NO_MODE, data,
+					      SMB2_OP_QUERY_INFO, cfile, NULL, NULL,
+					      NULL, NULL);
+			goto out;
+		} else if (rc != -EREMOTE && IS_ENABLED(CONFIG_CIFS_DFS_UPCALL) &&
+			   hdr->Status == STATUS_OBJECT_NAME_INVALID) {
+			/*
+			 * Handle weird Windows SMB server behaviour. It responds with
+			 * STATUS_OBJECT_NAME_INVALID code to SMB2 QUERY_INFO request
+			 * for "\<server>\<dfsname>\<linkpath>" DFS reference,
+			 * where <dfsname> contains non-ASCII unicode symbols.
+			 */
+			rc = -EREMOTE;
+		}
+		if (rc == -EREMOTE && IS_ENABLED(CONFIG_CIFS_DFS_UPCALL) && cifs_sb &&
+		    (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NO_DFS))
+			rc = -EOPNOTSUPP;
 	}
 
 out: