[PATCH 3/5] cifs: Improve SMB2+ stat() to work also on non-present name surrogate reparse points

["Pali Rohár" <pali@kernel.org>]

SMB server returns STATUS_OBJECT_PATH_NOT_FOUND if the path exists, is the
reparse point of name surrogate type (e.g. mount point) and surrogate
target location does not exist.

So if the server returns STATUS_OBJECT_PATH_NOT_FOUND error then it is
required to send request again with OPEN_REPARSE_POINT flag. This is needed
to distinguish between path does not exist and path exists and points to
non-existent surrogate location.

Before this change, Linux SMB client returned for non-present name
surrogate reparse point -ENOENT error. With this change it correctly
returns that the entry exits, it is of directory type with filled stat
information.

Signed-off-by: Pali Rohár <pali@kernel.org>
---
 fs/smb/client/smb2inode.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/fs/smb/client/smb2inode.c b/fs/smb/client/smb2inode.c
index 0b8d6d8f724d..b6342b043073 100644
--- a/fs/smb/client/smb2inode.c
+++ b/fs/smb/client/smb2inode.c
@@ -958,6 +958,18 @@ int smb2_query_path_info(const unsigned int xid,
 	if (!hdr || out_buftype[0] == CIFS_NO_BUFFER)
 		goto out;
 
+	/*
+	 * SMB server returns STATUS_OBJECT_PATH_NOT_FOUND if the path exists,
+	 * is the reparse point of name surrogate type (e.g. mount point) and
+	 * surrogate target location does not exist.
+	 * So if the server returns STATUS_OBJECT_PATH_NOT_FOUND error then it
+	 * is required to send request again with OPEN_REPARSE_POINT flag.
+	 * Re-opening with OPEN_REPARSE_POINT is done in the case when rc is
+	 * -EOPNOTSUPP.
+	 */
+	if (hdr->Status == STATUS_OBJECT_PATH_NOT_FOUND)
+		rc = -EOPNOTSUPP;
+
 	switch (rc) {
 	case 0:
 		rc = parse_create_response(data, cifs_sb, full_path, &out_iov[0]);
-- 
2.20.1